01 – Introduction to Russ, Lasers and Fiber Laser Marking (58:33)

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hi no my name’s Russ and I’d like to

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welcome you to this new series where I’m

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going to be exploring fiber laser

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marking machines well this one in

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particular we’ll talk about that in a

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second I think you could see I’m old I’m

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gray

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I’m Oakley I’m fat I’m also an ex

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engineer I’ve been involved in all

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aspects of engineering during my career

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and at one stage I own some co2 metal

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cutting laser machines so I thought I

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knew everything there was to know about

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nicer cutting until I got one of these

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Chinese machines and then all of a

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sudden I realized that I knew a lot

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about the machine and the way it’s

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rylynn the way it was maintained but

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nothing about the actual laser

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technology itself and so for the past

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four years I’ve been teaching myself

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very slowly but then again you’d expect

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that of somebody of my age wouldn’t you

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how these machines work what the

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technology is that makes them work

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successfully and I’ve been delving into

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some really dark corners that most

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people don’t bother to dig into these

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are hobby machines and lots of hobbyists

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just use them for small businesses or to

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play with yeah I play with mine as well

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but I specifically I’m an inquisitive

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person and I’d like to know how and why

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things work okay so I’m sitting here

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with my arm on a very nice

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fiber-optic laser marking machine why

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well we’re just about to start another

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learning journey into a different world

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of laces now the learning journey is

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mine maybe it’s yours as well but

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specifically I am the one that’s

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learning so always bear that in mind

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when you look at this when you watch

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these videos I can easily make mistakes

Transcript for Introduction to Fiber Laser Marking (Cont…)

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because there aren’t many people out

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there that can tell me a great deal

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about these machines they can tell me a

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lot about what they do and how they do

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it and the parameters that you need to

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set but that’s not what I’m after I want

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to dig into the dark corners and find

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out what this machine is really capable

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of let’s just give you a quick tour

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around the machine and then we’ll give

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you a quick demonstration first of all

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let’s take a look at the work area this

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is it no XY slides as you can see just a

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nice clean open work area with T slides

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in it so you can bolt down rotary unit

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if you want to this is a high-volume

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production marking machine now this is a

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product where the red anodized aluminium

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has been removed with a fiber laser you

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know every property three seconds go be

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another product offered in front of the

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laser this product is not flat the great

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advantage of this machine is it can mark

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non flat products because here’s the

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lens the lens is about 12 inches above

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the work surface and that means it’s an

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incredibly long focal length lens with

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quite a wide focal range on it so it can

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easily work over a curved surface like

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this now we can never get up inside the

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head to see what’s going on behind the

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lens so here’s the lens and that behind

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the lens we’ve got two mirrors one for x

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axis and one for y axis which is

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steering the beam that’s coming out of

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the laser machine now these are operated

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by two motors now these mirrors have got

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very very low mass and they can move

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incredibly quickly so the scanning speed

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of this machine I don’t know exactly

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what it is but I think it’s somewhere in

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the region about two meters a second

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which is incredibly fast but it’s all

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because of the low mass of these mirrors

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so that’s what’s hidden away up behind

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that lens there which I can’t get to

Transcript for Introduction to Fiber Laser Marking (Cont…)

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can’t just can’t do anything about it is

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what it is so the only thing that we can

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do to control this machine that’s assets

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and parameters that’s all I’ve got to

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play with now whether there are ways of

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defeating this software and going

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outside those limits I don’t know as yet

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I’ve got to investigate that but hey for

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the time being I think we’ll stay within

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the rules now at the back of the machine

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we’ve got a an extraction system and

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that’s what this cone is it’s an

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extraction system for pulling the fumes

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away from the engraving area now up in

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the machine there we’ve got a red box

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which is where all the clever

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fiber-optic work is being done or the

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electronic controls and here we’ve got

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the beam expanding system which takes

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the fiber-optic and opens the beam up

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ready to be processed by this lens here

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we’ve got a simple control panel at the

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front here with the emergency stop

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button and we’ve got a couple of key

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switches one which turns the machine on

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and off sorry this one turns the machine

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on and off and this one switches the

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interlocks on and off at the moment the

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interlock is on which means as soon as I

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press the start button this cover will

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come down and it will protect my eyes I

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can choose to operate it with the cover

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open like this which from time to time I

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should certainly be doing for you guys

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to show you what’s going on these were

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perfectly okay for protecting my eyes

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when I was working with the co2 laser

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but here we are on the fiber laser which

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is a different frequency of light I need

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to be a bit more careful with my eyes

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and when the guard is open I’m going to

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have to assume a Hollywood film star

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persona here we are on the co2 laser

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machine and we got to do a little teeny

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weeny bit of engraving and a speed and a

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power which is a close approximation to

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what we should be able to do on the

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now this is black anodized aluminium and

Transcript for Introduction to Fiber Laser Marking (Cont…)

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what we’re doing here we’re removing the

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black dye from the aluminium and leaving

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the aluminium oxide surface behind which

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is white okay now without changing

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anything I’m going to put a piece of

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glass over that then we’re going to

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repeat the same thing again so everybody

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with the co2 laser will recognize what

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I’ve done there I’ve been graved the

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surface of the glass and nothing no

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power at all has come through because

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the power has been a hundred percent

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absorbed by the glass okay so here we

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are on the fiber laser now I’m operating

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this machine at the moment with the

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guard open but I’ve got my film star

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goggles on and there’s a engraving that

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took place on the surface of the glass

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when we had it

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just there okay we’re now going to

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perform exactly the same trick on the

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favor

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so if I catch in the light right you can

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see that there is a mark on the back of

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the glass there it’s not on the front of

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the glass it’s a very very faint mark on

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the back of the glass there is a small

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amount of damage there to indicate it

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may well have done a little bit of

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engraving but it’s very very faint

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basically the glass has been completely

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transparent to infrared light at 1

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micron wavelength whereas at 10 point 6

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micron wavelengths the glass is

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completely opaque and the damage is

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taking place on the top surface here the

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energy is transferred right through the

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glass and it’s damaged the material

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underneath as though the glass wasn’t

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there look this was without the glass

Transcript for Introduction to Fiber Laser Marking (Cont…)

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and this was with the glass now after

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that little demonstration you may well

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now begin to understand that all lasers

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are not the same so I think we’ll start

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by explaining how a constant power co2

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laser works and then we’ll migrate from

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that into the fiber laser technology

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which is still a laser and the

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technology of lasing will still be the

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same and that’s what I think we must

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tackle before we even attempt to do

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anything with this machine I want to

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understand what it is that this machine

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is and can do I don’t even know what

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this machine is at the moment so how can

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I think about what it can do yet I could

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follow lots of YouTube clips and I could

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see lots of little parameter settings to

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make the machine do its tricks but

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that’s not what I’m about I want to

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understand why and how each one of those

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tricks can be done and how and why it

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takes place so

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this is not going to be an easy journey

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it’s going to be quite a technical

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journey but I am NOT a technical person

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I’m certainly not a physicist and I’m

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certainly not a chemist so anything that

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I described to you will be a very

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distilled and simplified version of the

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truth now before I get any further into

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this video I must just say a big thank

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you to the guys at Lotus laser systems

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they’ve taken the very brave step of

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entrusting this machine with me for one

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year they’ve lent it to me to play with

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as I’ve already started to tell you I

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know nothing about fiber laces so I’ve

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got this machine to just explore at my

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leisure now I have not in any way forced

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to make corporate videos Lotus laser

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system sounds like it should be a

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Chinese company these guys are only

Transcript for Introduction to Fiber Laser Marking (Cont…)

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probably about thirty miles up the road

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from me and they’re very easy to visit

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if I need to how much assistance have

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they given me with this machine the

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answer is very little at the moment

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they’ve installed it they’re showed me

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how to press all these buttons down at

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the bottom here they’re showing me

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roughly how the software works and

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they’ve given me a list of numbers and a

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little bit of paperwork that goes with

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the machine none of that paperwork tells

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me anything about how I make this

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machine perform the many tricks that it

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can perform but hey that’s going to be

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the fun of it ignorance is a great

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teacher too much knowledge gets in the

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way sometimes of digging into dark

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corners ignorance

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maybe allows me to dig into dark corners

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but I don’t even know a dark corners so

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we’ve got to build the foundations

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before we go anywhere near this machine

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now we’re going to start off with a very

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very simple atom got a small core or a

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nucleus and it’s got a charge a negative

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charge that Wizards around the outside

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of it in a little orbit just like a mini

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solar system the earth the moving

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running around the Earth now there are

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94 commonly found out

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months in this universe not just the

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world and each one of those elements has

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got a different mass in the centre and a

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different number of electrons floating

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in orbits around the outside of it now

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it’s very very usual for these atoms to

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not be on their own they like to exist

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with other atoms where they then become

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something called a molecule now

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molecules can either be two three four

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twenty atoms it depends on the

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complexity of what it is that you are

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looking at by whatever a material or a

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substance let’s forget about the larger

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picture and just come back to this very

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simple atom because this is all we need

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to understand lasing when this charge

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this electron gets a little bump of

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energy from somewhere it can move from

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this orbit to the next orbit out and

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here it is it’s now happily whizzing

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around in this orbit here but it’s not

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happy to stay in that orbit its natural

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orbit as this one so within a short

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period of time that could be anything

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from a millionth to a thousandth of a

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second it will drop back to this lower

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orbit now when it drops back it loses

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the energy that it gained when it went

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out to that orbit and it loses their

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energy in the form of a strange little

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thing called a and I’m going to draw it

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like this a photon of light we’re going

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to start looking at lasing in this form

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here which is the co2 gas tube laser the

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outer tube contains a gas mixture and

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that gas mixture also can run right

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through to the middle of the tube as

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well there are three tubes in there the

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outer one and the inner one are joined

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together right but around the outside of

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the inner tube we’ve got another tube

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which is full of water and that water is

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used to carry the heat away from the

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central tube

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now within this outer tube and obviously

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the inner tube as well we’ve got a mix

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of gases

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now all gases are basically non

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conductors of electricity now if we put

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25,000 volts across the end of this

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central tube the gas mix inside which

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contains nitrogen the nitrogen element

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of that gas mix will start to break down

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and release free electrons now these

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00:14:00.03 –> 00:14:05.760
things here are electrons and what

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00:14:03.9 –> 00:14:08.570
they’re basically doing is bursting free

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from their orbits and floating around

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and those free electrons are what are

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used to carry current through the tube

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electrical current through the tube so

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all of a sudden this nitrogen becomes a

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piece of almost resistance free wire it

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becomes conductive now we’re going to go

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to a real world tube now and I’m going

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to show you what happens when we put

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25,000 volts across the end the answer

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is nothing that you can see but then

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when we allow some current to flow

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through the nitrogen you’ll see that the

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colour or intensity of the glow in the

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tube is proportional to the amount of

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current that flows through the tube when

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you hear the little thing I’ve turned

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the 25,000 volts on now there was

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nothing happening when I turned to

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25,000 volts on

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okay so they’re now going to allow a

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00:15:04.91 –> 00:15:10.579
very small amount of current to pass

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through the tube as well as the high

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voltage you can just about see a little

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bit of a pink glow at the end of the

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tube there I’m now going to allow more

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current to flow through the tube

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[Music]

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I’m now going to put the maximum

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allowable current through the tube

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[Music]

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I think you can see clearly the

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different intensity of light coming from

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the tube if I allow more than a certain

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amount of current to pass through the

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00:15:50.16 –> 00:15:54.450
tube some very strange things happen

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okay so now you’ve seen this lovely pink

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00:15:54.45 –> 00:15:59.220
glow that happens down the inside of the

Transcript for Introduction to Fiber Laser Marking (Cont…)

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00:15:56.94 –> 00:16:01.279
tube basically this is lightning in a

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00:15:59.22 –> 00:16:05.640
bottle the more current I put through it

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00:16:01.279 –> 00:16:10.260
the more heat is being generated within

351
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the nitrogen itself and this element

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00:16:10.26 –> 00:16:18.060
here the helium 80 percent of it is

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00:16:14.089 –> 00:16:21.150
actually being used only as a means of

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00:16:18.06 –> 00:16:23.339
transporting that heat out to the water

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00:16:21.15 –> 00:16:25.070
jacket here where the heat is carried

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00:16:23.339 –> 00:16:28.200
away and the whole system remains

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thermally stable now mixed in to this

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gas not only we got helium we’ve also

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00:16:31.95 –> 00:16:37.440
got carbon dioxide a carbon dioxide

360
00:16:34.71 –> 00:16:41.790
molecule because it’s made up of carbon

361
00:16:37.44 –> 00:16:43.230
and two oxygen atoms bonded together so

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00:16:41.79 –> 00:16:46.230
we’re now going to change away from our

363
00:16:43.23 –> 00:16:48.630
little orbital picture to just looking

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00:16:46.23 –> 00:16:50.580
at the orbits themselves and what

365
00:16:48.63 –> 00:16:53.339
happens to these electrons it’s a much

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00:16:50.58 –> 00:16:55.800
easier picture to understand here we’ve

367
00:16:53.339 –> 00:16:58.260
got the ground state where the electron

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00:16:55.8 –> 00:17:00.600
starts then it goes up to its excited

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00:16:58.26 –> 00:17:02.550
state which is the next orbit out then

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00:17:00.6 –> 00:17:04.620
for a short period of time it may will

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00:17:02.55 –> 00:17:06.270
drop down to this something called a

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00:17:04.62 –> 00:17:07.920
metastable state which is an

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00:17:06.27 –> 00:17:11.420
intermediate state and then it drops

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00:17:07.92 –> 00:17:15.449
down all of the way and as it drops down

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00:17:11.42 –> 00:17:16.650
it gives out this photon of light now

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00:17:15.449 –> 00:17:19.890
I’m going to use this picture for two

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00:17:16.65 –> 00:17:22.140
situations the first situation is where

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00:17:19.89 –> 00:17:24.959
we put twenty-five thousand volts across

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00:17:22.14 –> 00:17:27.199
the nitrogen column and what then

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00:17:24.959 –> 00:17:29.309
happens is we shall knock some of these

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00:17:27.199 –> 00:17:32.760
electrons out of their ground state

382
00:17:29.309 –> 00:17:34.890
completely into a free orbit so they’re

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00:17:32.76 –> 00:17:36.570
floating around not all of them but just

384
00:17:34.89 –> 00:17:38.160
some of them and they’re there the

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00:17:36.57 –> 00:17:40.410
electrons that will be carrying their

386
00:17:38.16 –> 00:17:42.330
current now as soon as we ask for

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00:17:40.41 –> 00:17:45.000
current to flow those electrons they

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00:17:42.33 –> 00:17:48.090
will rush towards the positive end which

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is the 25,000 volt end of the tube and

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00:17:48.09 –> 00:17:52.950
as they rush along the tube so they will

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collide with other

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00:17:52.95 –> 00:18:00.570
nitrogen electrons as they collide they

Transcript for Introduction to Fiber Laser Marking (Cont…)

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00:17:56.13 –> 00:18:03.180
will promote those electrons up to an

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excited state now the action of

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00:18:03.18 –> 00:18:08.220
promoting electrons up to an excited

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00:18:05.37 –> 00:18:10.230
state is called pumping once they’ve

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00:18:08.22 –> 00:18:12.330
been pumped up to their excited state

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00:18:10.23 –> 00:18:14.070
they will stay there for a very short

399
00:18:12.33 –> 00:18:16.350
period of time now when they drop back

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00:18:14.07 –> 00:18:18.180
to their ground state they will give up

401
00:18:16.35 –> 00:18:20.430
the energy that they acquired here in

402
00:18:18.18 –> 00:18:23.310
the form of a photon of light now the

403
00:18:20.43 –> 00:18:26.580
photon of light that they give up is

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00:18:23.31 –> 00:18:29.460
pink that’s the action of the voltage

405
00:18:26.58 –> 00:18:34.020
and the current flowing through it which

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00:18:29.46 –> 00:18:36.720
is pumping the nitrogen atoms up to a

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00:18:34.02 –> 00:18:38.880
higher state and we’ve seen that pink go

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00:18:36.72 –> 00:18:42.090
in action now in the tube it’s the

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00:18:38.88 –> 00:18:43.710
collapse of excited nitrogen atoms going

410
00:18:42.09 –> 00:18:46.500
back to their ground state but the

411
00:18:43.71 –> 00:18:48.570
important thing here is this that we’ll

412
00:18:46.5 –> 00:18:53.190
think here which is the photon of light

413
00:18:48.57 –> 00:18:56.610
when they just drop back like this it’s

414
00:18:53.19 –> 00:18:58.860
a random action and that’s how you can

415
00:18:56.61 –> 00:19:00.330
see them because the pink is flying out

416
00:18:58.86 –> 00:19:02.010
the photons are flying out in all

417
00:19:00.33 –> 00:19:03.930
directions and some of them are

418
00:19:02.01 –> 00:19:07.110
finishing up at the back of your eye and

419
00:19:03.93 –> 00:19:11.010
you’re perceiving the pinkness of the

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00:19:07.11 –> 00:19:14.040
photon it is the photon here this action

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00:19:11.01 –> 00:19:17.550
of that photon which is going to then

422
00:19:14.04 –> 00:19:19.470
add energy to the carbon dioxide

423
00:19:17.55 –> 00:19:21.360
molecule and now we look at the same

424
00:19:19.47 –> 00:19:25.110
picture again so one of the electrons

425
00:19:21.36 –> 00:19:27.450
within the co2 molecule receives a

426
00:19:25.11 –> 00:19:31.320
little bit of pink energy from the

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00:19:27.45 –> 00:19:33.690
nitrogen and that knocks the electron up

428
00:19:31.32 –> 00:19:35.790
to its excited state the next orbit

429
00:19:33.69 –> 00:19:38.430
where it stays for a short period of

430
00:19:35.79 –> 00:19:40.560
time drops down to its metastable state

431
00:19:38.43 –> 00:19:44.040
and then will just fall back to ground

432
00:19:40.56 –> 00:19:48.530
emitting an invisible ten point six

433
00:19:44.04 –> 00:19:50.900
micron wavelength of infrared light

434
00:19:48.53 –> 00:19:54.480
something that you can’t see but again

435
00:19:50.9 –> 00:19:57.090
look it will be totally random because

436
00:19:54.48 –> 00:19:59.520
there is nothing to say that it must go

Transcript for Introduction to Fiber Laser Marking (Cont…)

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00:19:57.09 –> 00:20:01.410
in a particular direction you won’t be

438
00:19:59.52 –> 00:20:03.360
able to see it this time because it’s

439
00:20:01.41 –> 00:20:06.130
invisible but it’s still coming out of

440
00:20:03.36 –> 00:20:08.500
this tube it’s very very low

441
00:20:06.13 –> 00:20:13.710
random density so it’s not going to harm

442
00:20:08.5 –> 00:20:17.590
you now the word laser is acronym of

443
00:20:13.71 –> 00:20:20.320
light amplification by stimulated

444
00:20:17.59 –> 00:20:22.930
emission of radiation the important word

445
00:20:20.32 –> 00:20:26.680
here is stimulated what we’ve seen so

446
00:20:22.93 –> 00:20:28.630
far in both of these actions both the

447
00:20:26.68 –> 00:20:31.270
nitrogen and the carbon dioxide that

448
00:20:28.63 –> 00:20:36.130
we’ve mentioned so far has been random

449
00:20:31.27 –> 00:20:38.560
emission we get this light as the

450
00:20:36.13 –> 00:20:40.990
electron drops down from a high state to

451
00:20:38.56 –> 00:20:45.040
a ground state and we get this emission

452
00:20:40.99 –> 00:20:47.530
of radiation light and that’s what this

453
00:20:45.04 –> 00:20:51.100
is this is emission but it’s not

454
00:20:47.53 –> 00:20:54.010
stimulated it’s random so how do we get

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00:20:51.1 –> 00:20:55.960
from random emission to stimulated

456
00:20:54.01 –> 00:20:58.810
emission but well here I’ve got a

457
00:20:55.96 –> 00:21:01.480
picture of a very simplified gas tube

458
00:20:58.81 –> 00:21:04.510
we’ve ignored the water and all we’ve

459
00:21:01.48 –> 00:21:07.960
done we’ve got the electrodes here and

460
00:21:04.51 –> 00:21:10.030
we’ve got our column of ionized gas down

461
00:21:07.96 –> 00:21:12.460
the center and we’ve got all the other

462
00:21:10.03 –> 00:21:15.280
gas around the outside but at the end of

463
00:21:12.46 –> 00:21:19.600
the tube we’ve got the mirror and a

464
00:21:15.28 –> 00:21:21.610
mirror now there’s just not one of these

465
00:21:19.6 –> 00:21:24.010
actions taking place we’ve got millions

466
00:21:21.61 –> 00:21:26.950
of this actions taking place at any

467
00:21:24.01 –> 00:21:30.820
given point in time and so just by

468
00:21:26.95 –> 00:21:34.690
chance one of these photons will finish

469
00:21:30.82 –> 00:21:36.760
up traveling in this direction rather

470
00:21:34.69 –> 00:21:40.690
than any of the other directions that

471
00:21:36.76 –> 00:21:43.450
I’ve mentioned there now if that photon

472
00:21:40.69 –> 00:21:46.120
travels in this direction it’s going to

473
00:21:43.45 –> 00:21:47.860
hit this mirror and as it hits this

474
00:21:46.12 –> 00:21:52.380
mirror it’s going to bounce back and

475
00:21:47.86 –> 00:21:54.310
pass through the tube to the other end

476
00:21:52.38 –> 00:21:57.280
where it’s going to bounce off that

477
00:21:54.31 –> 00:21:59.830
mirror and come back so let’s change

Transcript for Introduction to Fiber Laser Marking (Cont…)

478
00:21:57.28 –> 00:22:02.700
pictures again so here we’ve got our

479
00:21:59.83 –> 00:22:06.250
pink photon pumping the carbon dioxide

480
00:22:02.7 –> 00:22:08.080
electron up to its excited level it then

481
00:22:06.25 –> 00:22:09.640
drops down to its lowest state and then

482
00:22:08.08 –> 00:22:12.430
one of these random photon emissions

483
00:22:09.64 –> 00:22:15.250
hacks happens to accidentally bump into

484
00:22:12.43 –> 00:22:18.130
the mirror at an absolutely

485
00:22:15.25 –> 00:22:19.690
perpendicular plane and as it does so it

486
00:22:18.13 –> 00:22:24.130
will drive back down

487
00:22:19.69 –> 00:22:28.660
this way now as it passes one of these

488
00:22:24.13 –> 00:22:32.050
excited electrons it’s a bit like the

489
00:22:28.66 –> 00:22:34.060
Pied Piper saying come and join me it’s

490
00:22:32.05 –> 00:22:37.510
a very strange phenomenon that happens

491
00:22:34.06 –> 00:22:40.930
when any when a photon travelling in

492
00:22:37.51 –> 00:22:43.510
this direction can attract this to go

493
00:22:40.93 –> 00:22:46.680
down to its low level and emit a photon

494
00:22:43.51 –> 00:22:50.080
on the way that perfectly matches the

495
00:22:46.68 –> 00:22:52.150
one that’s travelling by it so as a

496
00:22:50.08 –> 00:22:54.280
consequence what you will get you’ll get

497
00:22:52.15 –> 00:22:57.160
these photons being collected and

498
00:22:54.28 –> 00:22:59.020
they’re completely synchronized as shown

499
00:22:57.16 –> 00:23:01.930
by this picture and they will be

500
00:22:59.02 –> 00:23:04.750
traveling in this direction until I hit

501
00:23:01.93 –> 00:23:06.850
the mirror at this end and then they

502
00:23:04.75 –> 00:23:08.320
will all come back now as they’re

503
00:23:06.85 –> 00:23:12.030
traveling this way they will be

504
00:23:08.32 –> 00:23:16.420
collecting more photons and causing

505
00:23:12.03 –> 00:23:18.490
stimulated emissions from the electrons

506
00:23:16.42 –> 00:23:21.520
that they are causing to drop down to

507
00:23:18.49 –> 00:23:25.900
their ground state and this action here

508
00:23:21.52 –> 00:23:29.020
of photons passing by excited electrons

509
00:23:25.9 –> 00:23:32.020
is the stimulated emission effect that

510
00:23:29.02 –> 00:23:35.620
you want that produces a laser now this

511
00:23:32.02 –> 00:23:38.140
is a laser beam everything is fully in

512
00:23:35.62 –> 00:23:41.950
phase it’s what they call a coherent

513
00:23:38.14 –> 00:23:44.380
beam and I suppose the best equivalent I

514
00:23:41.95 –> 00:23:47.170
can give to you of what this is the

515
00:23:44.38 –> 00:23:49.810
power that this has is you’re quite

516
00:23:47.17 –> 00:23:52.390
happy to stand out in the rain and have

517
00:23:49.81 –> 00:23:54.790
raindrops hit you but would you be happy

518
00:23:52.39 –> 00:23:57.460
to stand in front of a tsunami wave it’s

519
00:23:54.79 –> 00:24:00.010
the same stuff it’s water but it’s all

Transcript for Introduction to Fiber Laser Marking (Cont…)

520
00:23:57.46 –> 00:24:02.110
acting in harmony you can imagine the

521
00:24:00.01 –> 00:24:04.120
difference between rain and a tsunami

522
00:24:02.11 –> 00:24:06.240
wave now that’s not necessarily a

523
00:24:04.12 –> 00:24:08.980
perfect analogy but it gives the idea

524
00:24:06.24 –> 00:24:11.590
you know once you get things working in

525
00:24:08.98 –> 00:24:13.930
harmony they gain strength so we get

526
00:24:11.59 –> 00:24:16.450
this group of let’s call them soldiers

527
00:24:13.93 –> 00:24:18.730
all marching together down to this end

528
00:24:16.45 –> 00:24:20.050
they bounce off that mirror and of

529
00:24:18.73 –> 00:24:22.470
course by the time they bounce off that

530
00:24:20.05 –> 00:24:26.140
mirror not only have they collected more

531
00:24:22.47 –> 00:24:28.300
troops as they go down the road they hit

532
00:24:26.14 –> 00:24:30.730
the mirror and they come back now by the

533
00:24:28.3 –> 00:24:31.779
time they come back we’ve got more pink

534
00:24:30.73 –> 00:24:35.109
electrons

535
00:24:31.779 –> 00:24:37.869
promoted more carbon dioxide atoms up to

536
00:24:35.109 –> 00:24:40.239
their excited state and so as the army

537
00:24:37.869 –> 00:24:43.479
comes back it grows because it collects

538
00:24:40.239 –> 00:24:45.369
more soldiers all marching together and

539
00:24:43.479 –> 00:24:48.119
then it goes that wasn’t for words like

540
00:24:45.369 –> 00:24:51.729
this and this is the amplification of

541
00:24:48.119 –> 00:24:53.739
the light of the mirrors yes it’s no

542
00:24:51.729 –> 00:24:56.229
longer a random emission it’s a

543
00:24:53.739 –> 00:24:59.440
stimulated emission by virtue of other

544
00:24:56.229 –> 00:25:02.070
photons collecting photons so this is

545
00:24:59.44 –> 00:25:04.359
the strange action of how a laser works

546
00:25:02.07 –> 00:25:07.029
so back to our little picture here now

547
00:25:04.359 –> 00:25:09.669
and we can see this backwards and

548
00:25:07.029 –> 00:25:12.399
forwards motion up and down the tube the

549
00:25:09.669 –> 00:25:14.710
pink photons are contained within the

550
00:25:12.399 –> 00:25:16.119
tube but of course coming out the end of

551
00:25:14.71 –> 00:25:18.279
the tube here we’ve got invisible

552
00:25:16.119 –> 00:25:20.769
photons at ten point six microns

553
00:25:18.279 –> 00:25:22.749
infrared wavelength which are bouncing

554
00:25:20.769 –> 00:25:25.599
up and down inside the tube there the

555
00:25:22.749 –> 00:25:27.279
laser is the invisible army that’s

556
00:25:25.599 –> 00:25:29.649
marching up and down backwards and

557
00:25:27.279 –> 00:25:32.080
forwards here and when it gets to this

558
00:25:29.649 –> 00:25:34.359
end we don’t have a hundred percent

559
00:25:32.08 –> 00:25:36.879
mirror what we’ve got is a 90 percent

560
00:25:34.359 –> 00:25:38.469
mirror I say 90 percent because that’s

561
00:25:36.879 –> 00:25:40.809
just my guess I don’t know what the

562
00:25:38.469 –> 00:25:44.320
exact number is but the net result is

563
00:25:40.809 –> 00:25:48.249
that for example we get a 10% of the

564
00:25:44.32 –> 00:25:51.399
army escaping this is our laser beam

565
00:25:48.249 –> 00:25:53.399
that we are going to use okay now the

566
00:25:51.399 –> 00:25:57.549
rest of it is being sent back to

567
00:25:53.399 –> 00:26:02.080
regenerate more laser beam for us to use

Transcript for Introduction to Fiber Laser Marking (Cont…)

568
00:25:57.549 –> 00:26:05.080
and so this becomes a stable generation

569
00:26:02.08 –> 00:26:07.570
of a constant output laser beam within

570
00:26:05.08 –> 00:26:10.210
the hv power supply not only is it

571
00:26:07.57 –> 00:26:12.759
generating this 25,000 volts across the

572
00:26:10.21 –> 00:26:15.309
end here it’s also got a current

573
00:26:12.759 –> 00:26:17.409
limiting system in there and so when you

574
00:26:15.309 –> 00:26:19.570
specify that you want a certain power

575
00:26:17.409 –> 00:26:21.249
what you’re really specifying is you

576
00:26:19.57 –> 00:26:25.719
want to allow a certain amount of

577
00:26:21.249 –> 00:26:27.700
current to flow through the tube okay

578
00:26:25.719 –> 00:26:30.369
now as I’ve already described to you the

579
00:26:27.7 –> 00:26:32.710
current flowing through the tube is in

580
00:26:30.369 –> 00:26:33.969
fact causing a heating effect now I’m

581
00:26:32.71 –> 00:26:36.339
going to stop at this point in time

582
00:26:33.969 –> 00:26:39.700
because there is a very very important

583
00:26:36.339 –> 00:26:41.710
physics principle that I must explain to

584
00:26:39.7 –> 00:26:45.060
you now you all know what temperature is

585
00:26:41.71 –> 00:26:48.400
but how do you define temperature

586
00:26:45.06 –> 00:26:50.650
it’s hot it’s cold you measure it with a

587
00:26:48.4 –> 00:26:52.900
thermometer but there isn’t a definition

588
00:26:50.65 –> 00:26:57.820
of temperature let me try and explain in

589
00:26:52.9 –> 00:27:00.550
a very simple way there we go believe me

590
00:26:57.82 –> 00:27:04.510
that everything that you see every

591
00:27:00.55 –> 00:27:07.930
molecule every atom is busy doing this

592
00:27:04.51 –> 00:27:10.870
at room temperature it’s shaking it’s

593
00:27:07.93 –> 00:27:15.370
vibrating now as you lower the

594
00:27:10.87 –> 00:27:19.710
temperature to minus 273 degrees C what

595
00:27:15.37 –> 00:27:24.070
happens is all molecular motion ceases

596
00:27:19.71 –> 00:27:26.310
so therefore by default if we raise the

597
00:27:24.07 –> 00:27:28.660
temperature back up to room temperature

598
00:27:26.31 –> 00:27:32.680
everything all the molecules all the

599
00:27:28.66 –> 00:27:36.040
atoms start vibrating so the level of

600
00:27:32.68 –> 00:27:38.920
vibration in a molecule or atom is a

601
00:27:36.04 –> 00:27:42.010
definition of its temperature this power

602
00:27:38.92 –> 00:27:45.880
supply has got the ability to control

603
00:27:42.01 –> 00:27:48.700
the current through this tube but the

604
00:27:45.88 –> 00:27:51.880
power supply can actually supply a lot

605
00:27:48.7 –> 00:27:56.080
more current than the tube is allowed to

606
00:27:51.88 –> 00:27:59.530
carry now this is a strange property of

Transcript for Introduction to Fiber Laser Marking (Cont…)

607
00:27:56.08 –> 00:28:02.440
gas tubes which will not exist within

608
00:27:59.53 –> 00:28:04.300
the fiber laser but I need to explain it

609
00:28:02.44 –> 00:28:07.360
just briefly so that you understand the

610
00:28:04.3 –> 00:28:09.220
problem if we allow too much current to

611
00:28:07.36 –> 00:28:12.970
flow through the nitrogen the nitrogen

612
00:28:09.22 –> 00:28:17.500
becomes super excited because it becomes

613
00:28:12.97 –> 00:28:21.430
hotter remember hotter motion more

614
00:28:17.5 –> 00:28:24.910
motion hotter the energy of collision

615
00:28:21.43 –> 00:28:27.670
can actually break an oxygen away from

616
00:28:24.91 –> 00:28:30.580
the carbon dioxide molecule and turn it

617
00:28:27.67 –> 00:28:33.580
into carbon monoxide than oxygen this is

618
00:28:30.58 –> 00:28:37.210
a process called dissociation and this

619
00:28:33.58 –> 00:28:40.450
is what happens when you overdrive a gas

620
00:28:37.21 –> 00:28:41.710
tube you actually destroy the one thing

621
00:28:40.45 –> 00:28:44.590
that’s in there that gives you the

622
00:28:41.71 –> 00:28:48.160
lasing action which is carbon dioxide so

623
00:28:44.59 –> 00:28:51.970
you must never overdrive your carbon

624
00:28:48.16 –> 00:28:55.150
dioxide gas laser tube now this oxygen

625
00:28:51.97 –> 00:28:57.510
was floating around free in here it will

626
00:28:55.15 –> 00:28:59.790
possibly finish up floating around and

627
00:28:57.51 –> 00:29:03.240
and color and clogging up the cathode

628
00:28:59.79 –> 00:29:04.830
making it less efficient there are other

629
00:29:03.24 –> 00:29:07.290
mechanisms going on in there which I’m

630
00:29:04.83 –> 00:29:09.930
not going to explain but the net result

631
00:29:07.29 –> 00:29:11.840
is that you must be very careful when

632
00:29:09.93 –> 00:29:18.030
you’ve got a gas tube that you do not

633
00:29:11.84 –> 00:29:20.340
overdrive it now a typical gas 260 50

634
00:29:18.03 –> 00:29:24.510
Watts will be about a thousand

635
00:29:20.34 –> 00:29:26.910
millimeters long from end to end now the

636
00:29:24.51 –> 00:29:27.810
speed of light is such and we’ll talk

637
00:29:26.91 –> 00:29:31.290
about this later

638
00:29:27.81 –> 00:29:33.930
that it takes about three billions of a

639
00:29:31.29 –> 00:29:36.360
second for this action to take place

640
00:29:33.93 –> 00:29:38.190
backwards and forwards so three

641
00:29:36.36 –> 00:29:40.320
billionth of a second that way and three

642
00:29:38.19 –> 00:29:43.440
billionths of a second that way is all

643
00:29:40.32 –> 00:29:45.930
it takes for these photons to go so it’s

644
00:29:43.44 –> 00:29:47.400
virtually instantaneous okay so now

645
00:29:45.93 –> 00:29:50.040
you’re armed with all the information

646
00:29:47.4 –> 00:29:51.840
you need to understand how lacing works

647
00:29:50.04 –> 00:29:54.840
very quick summary

648
00:29:51.84 –> 00:29:57.210
you need a photon to bump into an

649
00:29:54.84 –> 00:29:58.710
electron which will promote the electron

650
00:29:57.21 –> 00:30:00.810
up to a higher energy level

Transcript for Introduction to Fiber Laser Marking (Cont…)

651
00:29:58.71 –> 00:30:02.400
something called the excited state where

652
00:30:00.81 –> 00:30:06.960
it could stay for a short period of time

653
00:30:02.4 –> 00:30:10.230
until a photon drifts by and encourages

654
00:30:06.96 –> 00:30:12.210
this excited state to drop down back to

655
00:30:10.23 –> 00:30:14.580
its ground state and as it drops back to

656
00:30:12.21 –> 00:30:17.400
its ground state it emits a photon of

657
00:30:14.58 –> 00:30:20.310
energy which matches the photon that

658
00:30:17.4 –> 00:30:23.970
encouraged the drop and then we need

659
00:30:20.31 –> 00:30:27.390
mirrors to encourage amplification those

660
00:30:23.97 –> 00:30:29.400
are the basics of a laser we’re now

661
00:30:27.39 –> 00:30:32.520
going to enter the amazing world of the

662
00:30:29.4 –> 00:30:36.210
fiber laser now as I said to you before

663
00:30:32.52 –> 00:30:37.770
a laser is a laser but there’s going to

664
00:30:36.21 –> 00:30:40.440
be a few differences here that we need

665
00:30:37.77 –> 00:30:41.970
to deal with it’s quite important that

666
00:30:40.44 –> 00:30:46.080
we understand a couple of things first

667
00:30:41.97 –> 00:30:48.990
of all the speed of light 186,000 miles

668
00:30:46.08 –> 00:30:50.850
per second in a vacuum let’s not get too

669
00:30:48.99 –> 00:30:53.820
picky about the vacuum surely let’s just

670
00:30:50.85 –> 00:30:57.510
assume that it’s also the same as 300

671
00:30:53.82 –> 00:30:59.640
million meters per second now this might

672
00:30:57.51 –> 00:31:01.620
seem a huge number but in fact it’s

673
00:30:59.64 –> 00:31:03.810
probably an easier number to work with

674
00:31:01.62 –> 00:31:05.850
let’s just move on to time everybody

675
00:31:03.81 –> 00:31:09.390
knows what one second is you can imagine

676
00:31:05.85 –> 00:31:10.840
that can you imagine what a millisecond

677
00:31:09.39 –> 00:31:13.740
is 1,000

678
00:31:10.84 –> 00:31:15.970
of a second how about when we go to a

679
00:31:13.74 –> 00:31:19.120
microsecond which is a millionth of a

680
00:31:15.97 –> 00:31:20.830
second I’m sure nobody can actually

681
00:31:19.12 –> 00:31:23.259
imagine what a millionth of a second

682
00:31:20.83 –> 00:31:25.929
feels like looks like or sounds like so

683
00:31:23.259 –> 00:31:28.779
we’re then go and times smaller than a

684
00:31:25.929 –> 00:31:32.070
microsecond and it’s called a nanosecond

685
00:31:28.779 –> 00:31:35.169
let’s relate the speed of light

686
00:31:32.07 –> 00:31:37.419
to time if we do some very simple maths

687
00:31:35.169 –> 00:31:41.139
like just just get rid of these notes

688
00:31:37.419 –> 00:31:42.789
here and we’ll get rid of those two

689
00:31:41.139 –> 00:31:46.119
notes there and two notes there

690
00:31:42.789 –> 00:31:50.350
what we find is that in one nanosecond

691
00:31:46.119 –> 00:31:51.850
we travel 0.3 of a meter so everybody

692
00:31:50.35 –> 00:31:55.570
can imagine what point three of a meter

693
00:31:51.85 –> 00:31:59.940
is it’s about a foot and that’s how far

Transcript for Introduction to Fiber Laser Marking (Cont…)

694
00:31:55.57 –> 00:32:03.340
light travels in a billionth of a second

695
00:31:59.94 –> 00:32:05.019
unimaginable numbers but they will

696
00:32:03.34 –> 00:32:07.659
become important to us as we start

697
00:32:05.019 –> 00:32:09.129
delving further into fiber optics we’ve

698
00:32:07.659 –> 00:32:11.470
now finished with the world of glass

699
00:32:09.129 –> 00:32:13.690
tubes and something that’s

700
00:32:11.47 –> 00:32:17.049
understandable and we’re going to move

701
00:32:13.69 –> 00:32:22.059
down into some atomically small world

702
00:32:17.049 –> 00:32:25.899
where things act very very strange I’ve

703
00:32:22.059 –> 00:32:30.549
drawn a picture here of a typical piece

704
00:32:25.899 –> 00:32:32.470
of fiber basically what we’ve got is two

705
00:32:30.549 –> 00:32:36.580
pieces of material here we’ve got this

706
00:32:32.47 –> 00:32:41.679
core in the center here which is shown

707
00:32:36.58 –> 00:32:45.129
as being either 8 microns diameter or 50

708
00:32:41.679 –> 00:32:47.139
microns diameter now eight microns

709
00:32:45.129 –> 00:32:49.659
diameter is only major and really small

710
00:32:47.139 –> 00:32:53.320
you may or may not be able to see just

711
00:32:49.659 –> 00:32:55.960
here two hairs this is a gray hair of my

712
00:32:53.32 –> 00:33:02.289
head and that is probably three times

713
00:32:55.96 –> 00:33:05.259
thicker than that 8 micron core the 50

714
00:33:02.289 –> 00:33:07.840
microns which here is probably much

715
00:33:05.259 –> 00:33:09.570
closer to this hair here which is a

716
00:33:07.84 –> 00:33:12.970
remnant of one of my ex-girlfriends

717
00:33:09.57 –> 00:33:15.429
this is the sort of magnitude that we’re

718
00:33:12.97 –> 00:33:17.889
talking about to be able to get ten or

719
00:33:15.429 –> 00:33:21.869
twelve kilowatts of energy out of

720
00:33:17.889 –> 00:33:23.750
something that diameter is unimaginable

721
00:33:21.869 –> 00:33:25.730
but it happens

722
00:33:23.75 –> 00:33:27.980
now the way in which the last laser tube

723
00:33:25.73 –> 00:33:30.980
was working was very simple we were

724
00:33:27.98 –> 00:33:35.510
creating pink light energy in this

725
00:33:30.98 –> 00:33:38.260
central tube and in here also was carbon

726
00:33:35.51 –> 00:33:42.050
dioxide and that was the carbon dioxide

727
00:33:38.26 –> 00:33:44.540
that was being stimulated to create a

728
00:33:42.05 –> 00:33:46.220
laser output we had a mirror at each end

729
00:33:44.54 –> 00:33:48.470
and the whole thing was bouncing

730
00:33:46.22 –> 00:33:50.210
backwards and forwards this being a 90%

731
00:33:48.47 –> 00:33:54.830
mirror and we were getting output from

732
00:33:50.21 –> 00:33:57.760
here so with the fiber laser what we do

733
00:33:54.83 –> 00:34:01.880
we inject the light from the outside

Transcript for Introduction to Fiber Laser Marking (Cont…)

734
00:33:57.76 –> 00:34:04.730
into this outside core this blue outer

735
00:34:01.88 –> 00:34:07.340
cladding as they call it okay now as

736
00:34:04.73 –> 00:34:11.389
that light bounces around it crosses

737
00:34:07.34 –> 00:34:14.600
over and interferes with this red core

738
00:34:11.389 –> 00:34:16.810
down the center now the red core down

739
00:34:14.6 –> 00:34:20.510
the center is a rather special material

740
00:34:16.81 –> 00:34:23.629
it’s a core made of silica glass doped

741
00:34:20.51 –> 00:34:25.909
with a rare earth called ytterbium now I

742
00:34:23.629 –> 00:34:29.330
know it says why there to begin to start

743
00:34:25.909 –> 00:34:33.080
with but why has actually said I so it’s

744
00:34:29.33 –> 00:34:36.260
ytterbium doped basically means it’s got

745
00:34:33.08 –> 00:34:37.570
a high percentage of ytterbium included

746
00:34:36.26 –> 00:34:40.490
in the glass

747
00:34:37.57 –> 00:34:42.980
whereas this outer sheath with a

748
00:34:40.49 –> 00:34:47.750
different refractive index I’m not going

749
00:34:42.98 –> 00:34:50.240
to explain that is just ordinary silica

750
00:34:47.75 –> 00:34:52.550
glass and it’s the difference in the

751
00:34:50.24 –> 00:34:55.639
refractive index of these two materials

752
00:34:52.55 –> 00:34:59.210
that causes the strange phenomena called

753
00:34:55.639 –> 00:35:02.360
total internal reflection and as you can

754
00:34:59.21 –> 00:35:06.080
see here we’ve got a red beam which is

755
00:35:02.36 –> 00:35:09.830
our power beam and it’s keeping to its

756
00:35:06.08 –> 00:35:14.210
own motorway which is the thin core down

757
00:35:09.83 –> 00:35:16.490
the center now this material in here

758
00:35:14.21 –> 00:35:18.070
called ytterbium has got some very

759
00:35:16.49 –> 00:35:22.820
interesting properties

760
00:35:18.07 –> 00:35:25.310
whereas with our co2 and a nitrogen we

761
00:35:22.82 –> 00:35:30.470
had something called an excited state

762
00:35:25.31 –> 00:35:33.350
and a a saw semi permanent state which

763
00:35:30.47 –> 00:35:34.750
is called a metastable state where it

764
00:35:33.35 –> 00:35:37.590
dropped down from there

765
00:35:34.75 –> 00:35:41.110
metastable state to the ground state

766
00:35:37.59 –> 00:35:44.410
with ytterbium we only have two states

767
00:35:41.11 –> 00:35:46.330
we’ve got a ground state and an excited

768
00:35:44.41 –> 00:35:48.840
state and relatively speaking this

769
00:35:46.33 –> 00:35:51.280
excited state can last quite a long time

770
00:35:48.84 –> 00:35:54.250
so we have no difference in the

771
00:35:51.28 –> 00:35:55.990
principle of lacing we’re just using a

772
00:35:54.25 –> 00:35:57.610
different material we’re using a solid

773
00:35:55.99 –> 00:36:01.240
material as opposed to a gas

Transcript for Introduction to Fiber Laser Marking (Cont…)

774
00:35:57.61 –> 00:36:03.250
so we pump light in and as you can see

775
00:36:01.24 –> 00:36:05.410
the light as gradually decreasing as we

776
00:36:03.25 –> 00:36:08.380
go along the fiber because we are

777
00:36:05.41 –> 00:36:12.150
gradually converting more and more of

778
00:36:08.38 –> 00:36:15.550
these ytterbium into high energy state

779
00:36:12.15 –> 00:36:17.530
which are then being released as the

780
00:36:15.55 –> 00:36:19.390
light bounces backwards and forwards of

781
00:36:17.53 –> 00:36:20.740
these two mirrors on the end here now

782
00:36:19.39 –> 00:36:22.720
although this is a general

783
00:36:20.74 –> 00:36:25.840
representation to give you the idea of

784
00:36:22.72 –> 00:36:28.060
how a fiber optic laser works it doesn’t

785
00:36:25.84 –> 00:36:30.070
actually work like this in reality at

786
00:36:28.06 –> 00:36:32.140
all now I’m not gonna go too far away

787
00:36:30.07 –> 00:36:34.390
from my diagram here but I am going to

788
00:36:32.14 –> 00:36:38.520
say that we don’t have real mirrors on

789
00:36:34.39 –> 00:36:41.890
the end of the fiber they manipulate the

790
00:36:38.52 –> 00:36:44.650
diameter of this central core in such a

791
00:36:41.89 –> 00:36:46.660
way it’s something called a brake

792
00:36:44.65 –> 00:36:48.850
grating which you can look that up and

793
00:36:46.66 –> 00:36:52.690
find out more about it which either

794
00:36:48.85 –> 00:36:55.300
causes complete reflection or partial

795
00:36:52.69 –> 00:36:58.240
reflection so we have the same effect as

796
00:36:55.3 –> 00:37:02.230
mirrors but without mirrors I’ve shown

797
00:36:58.24 –> 00:37:05.950
this is a very short section of fiber in

798
00:37:02.23 –> 00:37:09.490
reality this could be one two three six

799
00:37:05.95 –> 00:37:12.250
meters long it really depends on how

800
00:37:09.49 –> 00:37:14.410
much energy you want to store in the

801
00:37:12.25 –> 00:37:18.190
system okay now a few moments ago we

802
00:37:14.41 –> 00:37:21.040
talked about huge power capability out

803
00:37:18.19 –> 00:37:23.350
of these lasers but in reality it’s not

804
00:37:21.04 –> 00:37:25.780
quite as phenomenal as you might imagine

805
00:37:23.35 –> 00:37:28.690
we’re not talking about 12 kilowatts of

806
00:37:25.78 –> 00:37:31.960
continuous power we’re talking about the

807
00:37:28.69 –> 00:37:34.090
very very short duration pulse so in

808
00:37:31.96 –> 00:37:36.190
this world of fiber lasers marking

809
00:37:34.09 –> 00:37:38.770
machines which will come across two

810
00:37:36.19 –> 00:37:40.420
types of laser the most common type of

811
00:37:38.77 –> 00:37:42.820
laser is something called a q-switched

812
00:37:40.42 –> 00:37:44.710
laser now they’re generally the cheaper

813
00:37:42.82 –> 00:37:46.630
type of laser that doesn’t mean to say

814
00:37:44.71 –> 00:37:47.099
that bad it just means to say there have

815
00:37:46.63 –> 00:37:49.019
got

816
00:37:47.099 –> 00:37:52.349
a certain amount of limitation on their

817
00:37:49.019 –> 00:37:53.999
capabilities but first of all let’s take

818
00:37:52.349 –> 00:37:57.769
a look at the q-switch laser because

Transcript for Introduction to Fiber Laser Marking (Cont…)

819
00:37:53.999 –> 00:38:01.890
this is a fairly simple jump from a

820
00:37:57.769 –> 00:38:02.880
continuous wave laser to explain how

821
00:38:01.89 –> 00:38:05.609
this one works

822
00:38:02.88 –> 00:38:07.979
now as you can see I’ve modified the

823
00:38:05.609 –> 00:38:10.170
drawing very slightly and I’ve included

824
00:38:07.979 –> 00:38:12.269
this thing in here called a cue switch

825
00:38:10.17 –> 00:38:14.459
so I’m not going to explain how a cue

826
00:38:12.269 –> 00:38:16.109
switch works you can go and befuddle

827
00:38:14.459 –> 00:38:18.059
your own brain if you want I’m just

828
00:38:16.109 –> 00:38:20.400
going to regard this as being a piece of

829
00:38:18.059 –> 00:38:23.940
electronic cotton wool for the purpose

830
00:38:20.4 –> 00:38:26.519
of my very simple mental model basically

831
00:38:23.94 –> 00:38:28.920
it stops anything from reaching this

832
00:38:26.519 –> 00:38:31.289
mirror here and bear in mind these are

833
00:38:28.92 –> 00:38:33.390
not real mirrors these are things called

834
00:38:31.289 –> 00:38:35.459
Bragg gratings but I’ve shown them as

835
00:38:33.39 –> 00:38:38.430
mirrors because that’s what the net

836
00:38:35.459 –> 00:38:41.940
effect is so here we’ve got a cue switch

837
00:38:38.43 –> 00:38:44.910
and here we’ve got our blue pumping

838
00:38:41.94 –> 00:38:49.109
laser and remember what pumping is

839
00:38:44.91 –> 00:38:51.989
pumping is pushing all the electrons

840
00:38:49.109 –> 00:38:54.930
that are in here up to a higher excited

841
00:38:51.989 –> 00:38:56.969
state if we turn our electronic cotton

842
00:38:54.93 –> 00:38:59.459
wall on and prevent anything from

843
00:38:56.969 –> 00:39:01.229
reaching this mirror the only thing

844
00:38:59.459 –> 00:39:03.119
that’s going to happen is we’re going to

845
00:39:01.229 –> 00:39:03.660
pump all these electrons that are in

846
00:39:03.119 –> 00:39:06.569
here

847
00:39:03.66 –> 00:39:08.479
up to there excited state we’re

848
00:39:06.569 –> 00:39:12.989
effectively going to be storing energy

849
00:39:08.479 –> 00:39:14.670
in this piece of fiber-optic material so

850
00:39:12.989 –> 00:39:17.099
we’ve stored as much in as with energy

851
00:39:14.67 –> 00:39:18.809
as we can in here and now we’ll turn out

852
00:39:17.099 –> 00:39:22.949
a piece of electronic cotton wall off

853
00:39:18.809 –> 00:39:24.509
and some photons will escape and come

854
00:39:22.949 –> 00:39:26.969
through here and bounce off this mirror

855
00:39:24.509 –> 00:39:29.249
now as soon as a photon bounces off this

856
00:39:26.969 –> 00:39:31.019
mirror and runs back we know what the

857
00:39:29.249 –> 00:39:33.989
effect is going to be it’s going to

858
00:39:31.019 –> 00:39:36.539
trigger a cascade effect as it travels

859
00:39:33.989 –> 00:39:39.209
back to this mirror and so here we go

860
00:39:36.539 –> 00:39:41.999
this is the same basic principle that

861
00:39:39.209 –> 00:39:44.459
we’ve already discussed so there’s

862
00:39:41.999 –> 00:39:46.380
nothing new here except that we’ve put

863
00:39:44.459 –> 00:39:48.479
this switch in the way what is the

864
00:39:46.38 –> 00:39:51.779
effect of this switch now it’s much

865
00:39:48.479 –> 00:39:54.989
easier to show you this in a

866
00:39:51.779 –> 00:39:58.140
diagrammatic form here we’ve got the

867
00:39:54.989 –> 00:39:59.700
blue section over time and we’re busy

868
00:39:58.14 –> 00:40:02.490
pumping

Transcript for Introduction to Fiber Laser Marking (Cont…)

869
00:39:59.7 –> 00:40:05.069
electrons up to their high energy state

870
00:40:02.49 –> 00:40:06.900
they’re excited state and here we’ve got

871
00:40:05.069 –> 00:40:10.309
a green line which shows the general

872
00:40:06.9 –> 00:40:12.900
progression over time of the amount of

873
00:40:10.309 –> 00:40:15.150
excited electrons they get more and more

874
00:40:12.9 –> 00:40:16.710
and more and more until we reach a point

875
00:40:15.15 –> 00:40:18.960
where there are no more electrons to

876
00:40:16.71 –> 00:40:21.240
excite and so consequently this line

877
00:40:18.96 –> 00:40:23.910
would then level out once we’ve reached

878
00:40:21.24 –> 00:40:26.760
this maximum point here where we cannot

879
00:40:23.91 –> 00:40:29.130
actually excite any more electrons up to

880
00:40:26.76 –> 00:40:31.380
there excited state Mars will turn off

881
00:40:29.13 –> 00:40:33.809
the cue switch we remove the cotton wool

882
00:40:31.38 –> 00:40:36.000
and will allow the photons to pass

883
00:40:33.809 –> 00:40:38.309
through and hit the mirror now it’ll be

884
00:40:36.0 –> 00:40:40.530
initially there’ll be one or two photons

885
00:40:38.309 –> 00:40:42.119
a few photons that hit then they’ll

886
00:40:40.53 –> 00:40:43.650
start bouncing backwards and forwards

887
00:40:42.119 –> 00:40:45.299
and as they bounce backwards and

888
00:40:43.65 –> 00:40:47.790
forwards we’ll get this amplification

889
00:40:45.299 –> 00:40:49.530
effect well it takes a little bit of

890
00:40:47.79 –> 00:40:51.750
time for the amplification effect to

891
00:40:49.53 –> 00:40:53.880
build up but once the amplification

892
00:40:51.75 –> 00:40:56.760
effect builds up we get this cascade

893
00:40:53.88 –> 00:41:00.420
that happens where we get a tremendous

894
00:40:56.76 –> 00:41:02.730
rush a conversion rate of electrons and

895
00:41:00.42 –> 00:41:05.490
they start dropping down producing

896
00:41:02.73 –> 00:41:07.380
photons huge numbers of photons and of

897
00:41:05.49 –> 00:41:09.839
course as we’ve seen what we’re really

898
00:41:07.38 –> 00:41:12.809
producing here is that photon tsunami

899
00:41:09.839 –> 00:41:15.420
wave you know all these all the photons

900
00:41:12.809 –> 00:41:17.819
working together and they will produce a

901
00:41:15.42 –> 00:41:19.829
very huge peak but of course as soon as

902
00:41:17.819 –> 00:41:23.430
we start to get this peak which will

903
00:41:19.829 –> 00:41:27.720
reach a crossover point where the number

904
00:41:23.43 –> 00:41:29.819
of electrons available to rush out into

905
00:41:27.72 –> 00:41:32.400
the real world starts dropping rapidly

906
00:41:29.819 –> 00:41:35.130
so all of a sudden we’ll reach this peak

907
00:41:32.4 –> 00:41:37.740
and we will drop off just as quickly as

908
00:41:35.13 –> 00:41:40.290
we started this is only a 20 watt laser

909
00:41:37.74 –> 00:41:44.790
so let’s just see what would happen if

910
00:41:40.29 –> 00:41:48.720
this was a continuous 20 watt laser as

911
00:41:44.79 –> 00:41:52.200
opposed to a pulsed 20 watt laser so

912
00:41:48.72 –> 00:41:55.079
here we are we’re pumping and here we

913
00:41:52.2 –> 00:41:57.930
are pumping but this time because it’s a

914
00:41:55.079 –> 00:42:01.380
continuous output we’ve also got this

Transcript for Introduction to Fiber Laser Marking (Cont…)

915
00:41:57.93 –> 00:42:03.299
leakage here and so we won’t in this

916
00:42:01.38 –> 00:42:07.559
particular instance of a continuous wave

917
00:42:03.299 –> 00:42:10.400
ever reach saturation what what happen

918
00:42:07.559 –> 00:42:12.960
is we shall pump and we shall get the

919
00:42:10.4 –> 00:42:16.560
which will get the excited it

920
00:42:12.96 –> 00:42:20.070
runs up to a certain amount let’s call

921
00:42:16.56 –> 00:42:23.490
it that amount okay and it will be

922
00:42:20.07 –> 00:42:26.070
stable because as we’re pumping

923
00:42:23.49 –> 00:42:30.690
electrons up to this higher level so

924
00:42:26.07 –> 00:42:33.780
they’re leaking away and here we’ve got

925
00:42:30.69 –> 00:42:34.830
our 20 watt output okay now to try and

926
00:42:33.78 –> 00:42:36.630
make this a little bit more

927
00:42:34.83 –> 00:42:39.119
understandable what I’d like you to do

928
00:42:36.63 –> 00:42:40.710
is imagine a bath now if the water

929
00:42:39.119 –> 00:42:43.859
running into the bath is slightly

930
00:42:40.71 –> 00:42:46.290
greater than the oil will go at the plug

931
00:42:43.859 –> 00:42:48.119
hole there will be a balance that will

932
00:42:46.29 –> 00:42:50.369
be achieved we’ll get a certain level of

933
00:42:48.119 –> 00:42:52.380
water in the bath such that the water

934
00:42:50.369 –> 00:42:55.310
can disappear out the plug hole at the

935
00:42:52.38 –> 00:42:58.500
same rate that it comes in from the tap

936
00:42:55.31 –> 00:43:01.830
and that’s the stability that’s shown in

937
00:42:58.5 –> 00:43:04.140
this situation here now when we talk

938
00:43:01.83 –> 00:43:07.349
about a cue switch what we’re really

939
00:43:04.14 –> 00:43:09.750
doing is we’re putting the plug in so we

940
00:43:07.349 –> 00:43:13.500
put the plug in the bath and the bath no

941
00:43:09.75 –> 00:43:15.330
fills up to overflowing and then we

942
00:43:13.5 –> 00:43:18.089
remove the plug and as we remove the

943
00:43:15.33 –> 00:43:20.460
plug look we get a rush of water back to

944
00:43:18.089 –> 00:43:23.130
the plug hole so that’s how we can

945
00:43:20.46 –> 00:43:26.220
produce very high power out of a very

946
00:43:23.13 –> 00:43:27.540
low power input we can store it up for a

947
00:43:26.22 –> 00:43:34.589
period of time and then release it

948
00:43:27.54 –> 00:43:38.040
instantly instantly hmm remember we

949
00:43:34.589 –> 00:43:40.490
talked about the speed of light how far

950
00:43:38.04 –> 00:43:44.730
things travel in one nanosecond

951
00:43:40.49 –> 00:43:49.980
well these pulses here we’re talking

952
00:43:44.73 –> 00:43:52.589
about maybe maybe as little as 5 to 10

953
00:43:49.98 –> 00:43:55.170
nanoseconds let’s just say 10

954
00:43:52.589 –> 00:43:57.210
nanoseconds so that means look we’ve

955
00:43:55.17 –> 00:44:01.260
also got another 10 nanoseconds here

Transcript for Introduction to Fiber Laser Marking (Cont…)

956
00:43:57.21 –> 00:44:06.890
which is to build up time so it’s taking

957
00:44:01.26 –> 00:44:11.099
10 nanoseconds to get our system running

958
00:44:06.89 –> 00:44:14.010
so if this system is only one meter long

959
00:44:11.099 –> 00:44:16.859
for example and we know that it takes

960
00:44:14.01 –> 00:44:20.040
roughly 3 nanoseconds to travel a meter

961
00:44:16.859 –> 00:44:22.200
and if this is a 10 or 12 nanoseconds

962
00:44:20.04 –> 00:44:23.520
here it means we’re going to have Rea

963
00:44:22.2 –> 00:44:27.780
maybe

964
00:44:23.52 –> 00:44:30.960
two round-trips of a photon to build up

965
00:44:27.78 –> 00:44:32.490
to this critical level so that’s why

966
00:44:30.96 –> 00:44:35.820
we’ve got a delay here we can’t

967
00:44:32.49 –> 00:44:38.340
instantly get power out of the switch

968
00:44:35.82 –> 00:44:42.360
there is a delay after you switch on

969
00:44:38.34 –> 00:44:44.580
before things happen because the speed

970
00:44:42.36 –> 00:44:47.190
of light is actually now getting in the

971
00:44:44.58 –> 00:44:48.600
way of the pulse generation and then the

972
00:44:47.19 –> 00:44:51.870
width of the pulse is basically

973
00:44:48.6 –> 00:44:54.540
determined by the speed at which you

974
00:44:51.87 –> 00:44:57.030
could convert excited electrons into

975
00:44:54.54 –> 00:44:58.650
photons and that again is determined by

976
00:44:57.03 –> 00:45:00.270
the speed of light traveling up and down

977
00:44:58.65 –> 00:45:02.610
the fiber so there are certain physical

978
00:45:00.27 –> 00:45:06.690
limitations as to what can happen with

979
00:45:02.61 –> 00:45:08.940
this pulse now we could reduce the

980
00:45:06.69 –> 00:45:10.380
amount of pumping time in other words we

981
00:45:08.94 –> 00:45:13.260
could we could make the cue switch

982
00:45:10.38 –> 00:45:15.780
switch earlier and if we make the cue

983
00:45:13.26 –> 00:45:17.910
switch switch earlier then what it means

984
00:45:15.78 –> 00:45:19.470
is that we shan’t produce as much of a

985
00:45:17.91 –> 00:45:24.050
pulse which will produce a smaller pulse

986
00:45:19.47 –> 00:45:27.930
like this but it will still be a pulse

987
00:45:24.05 –> 00:45:31.020
but at a much lower peak power so that’s

988
00:45:27.93 –> 00:45:33.420
one variable that they could use to play

989
00:45:31.02 –> 00:45:41.490
with a cue switch the second variable is

990
00:45:33.42 –> 00:45:44.520
the repeat interval here of the pulse it

991
00:45:41.49 –> 00:45:47.220
really depends on how how long the fiber

992
00:45:44.52 –> 00:45:49.950
is and how quickly it takes to reach

993
00:45:47.22 –> 00:45:52.860
this saturation point so that’s the

994
00:45:49.95 –> 00:45:54.330
principle of q-switch laser ok so

995
00:45:52.86 –> 00:45:56.250
eventually we get on to the most

996
00:45:54.33 –> 00:45:58.230
difficult part of my quest which is

997
00:45:56.25 –> 00:46:01.110
trying to understand how a moped laser

Transcript for Introduction to Fiber Laser Marking (Cont…)

998
00:45:58.23 –> 00:46:04.250
works it’s not the same there’s any

999
00:46:01.11 –> 00:46:08.390
other laser that we’ve talked about yes

1000
00:46:04.25 –> 00:46:14.820
it’s got core yes it’s got a cladding

1001
00:46:08.39 –> 00:46:17.130
but it has no mirrors so that was a big

1002
00:46:14.82 –> 00:46:20.480
problem I had to start with with no

1003
00:46:17.13 –> 00:46:24.960
mirrors but then I realized something

1004
00:46:20.48 –> 00:46:27.840
significantly different this one has an

1005
00:46:24.96 –> 00:46:31.440
injection of a signal down into the core

1006
00:46:27.84 –> 00:46:34.280
itself not just a pump signal but

1007
00:46:31.44 –> 00:46:37.730
actually a signal which runs through

1008
00:46:34.28 –> 00:46:41.600
both laces and comes out this end in a

1009
00:46:37.73 –> 00:46:43.970
fully amplified laser format how does

1010
00:46:41.6 –> 00:46:46.850
this actually work it’s quite

1011
00:46:43.97 –> 00:46:50.750
complicated optically but in principle

1012
00:46:46.85 –> 00:46:53.000
it’s very simple for me to explain now

1013
00:46:50.75 –> 00:46:55.010
bear in mind this explanation that I’ve

1014
00:46:53.0 –> 00:46:57.230
given you as the explanation that I’m

1015
00:46:55.01 –> 00:47:00.260
giving myself this is how I’ve

1016
00:46:57.23 –> 00:47:03.950
interpreted after many hours of reading

1017
00:47:00.26 –> 00:47:06.530
and research into mopus nobody has told

1018
00:47:03.95 –> 00:47:08.930
me exactly how this thing works what I’m

1019
00:47:06.53 –> 00:47:13.400
just about to tell you fits all the

1020
00:47:08.93 –> 00:47:16.100
facts that I have we energize the core

1021
00:47:13.4 –> 00:47:18.740
in here up to its fullest extent with

1022
00:47:16.1 –> 00:47:21.200
these pumping lasers and this is a

1023
00:47:18.74 –> 00:47:23.930
signal input something they call a seed

1024
00:47:21.2 –> 00:47:25.670
laser more about this in a second so

1025
00:47:23.93 –> 00:47:28.930
once you’ve got the population in here

1026
00:47:25.67 –> 00:47:32.510
fully saturated inverted and saturated

1027
00:47:28.93 –> 00:47:35.440
at the same in this one we’ve got the

1028
00:47:32.51 –> 00:47:38.420
pump laser which is busy pumping all the

1029
00:47:35.44 –> 00:47:41.300
electrons in this core up to their

1030
00:47:38.42 –> 00:47:43.550
saturation high energy level we can then

1031
00:47:41.3 –> 00:47:47.680
inject a signal into this end

1032
00:47:43.55 –> 00:47:53.000
so this photodiode sends a powerful beam

1033
00:47:47.68 –> 00:47:55.040
into the end here and it then runs right

1034
00:47:53.0 –> 00:47:58.040
the way through here collecting photons

1035
00:47:55.04 –> 00:48:01.120
as it goes and comes out the other end

Transcript for Introduction to Fiber Laser Marking (Cont…)

1036
00:47:58.04 –> 00:48:04.300
with more photons than it went in with

1037
00:48:01.12 –> 00:48:08.090
but then it transfers across to another

1038
00:48:04.3 –> 00:48:10.370
much bigger and wider beam with more

1039
00:48:08.09 –> 00:48:13.490
pumping this secondary fine but then

1040
00:48:10.37 –> 00:48:16.190
actually amplifies the signal this first

1041
00:48:13.49 –> 00:48:19.690
fiber is signal conditioning that it’s

1042
00:48:16.19 –> 00:48:22.640
generating the pulse shape that we want

1043
00:48:19.69 –> 00:48:24.380
but this one amplifies the pol shake

1044
00:48:22.64 –> 00:48:26.600
there is a small amount of pulse change

1045
00:48:24.38 –> 00:48:28.640
shaping taking place in here as well but

1046
00:48:26.6 –> 00:48:31.850
most of the shaping takes place in here

1047
00:48:28.64 –> 00:48:34.610
now it’s not necessarily from what I

1048
00:48:31.85 –> 00:48:36.620
understand conscious shaping it’s

1049
00:48:34.61 –> 00:48:39.320
something that happens because of the

1050
00:48:36.62 –> 00:48:41.270
natural properties of the fiber this is

1051
00:48:39.32 –> 00:48:43.160
how I’ve explained it to myself so we’ve

1052
00:48:41.27 –> 00:48:46.160
got full population inversion in the

1053
00:48:43.16 –> 00:48:49.099
center core there we then inject a small

1054
00:48:46.16 –> 00:48:52.640
million from this red laser and that

1055
00:48:49.099 –> 00:48:56.530
signal might look like that and that

1056
00:48:52.64 –> 00:49:00.619
might be say one and then a second white

1057
00:48:56.53 –> 00:49:03.770
now this here could be for instance four

1058
00:49:00.619 –> 00:49:05.680
meters long and this cable here might be

1059
00:49:03.77 –> 00:49:08.599
six meters long

1060
00:49:05.68 –> 00:49:11.480
they’re quite long these fiber-optic

1061
00:49:08.599 –> 00:49:15.319
cables now we already know that one

1062
00:49:11.48 –> 00:49:20.390
nanosecond equals roughly 300

1063
00:49:15.319 –> 00:49:22.309
millimeters so four meters it’s going to

1064
00:49:20.39 –> 00:49:24.020
take thirteen or fourteen nanoseconds to

1065
00:49:22.309 –> 00:49:26.599
travel down there but what we’ve got to

1066
00:49:24.02 –> 00:49:29.450
imagine is this once we inject the

1067
00:49:26.599 –> 00:49:32.539
signal and the signal goes in and it is

1068
00:49:29.45 –> 00:49:34.460
300 millimetres long so there we are

1069
00:49:32.539 –> 00:49:35.750
we’ve got have 300 millimetre long

1070
00:49:34.46 –> 00:49:38.180
signal going in there

1071
00:49:35.75 –> 00:49:40.700
and it’s going to travel along and

1072
00:49:38.18 –> 00:49:43.400
remain 300 millimeters all the way along

1073
00:49:40.7 –> 00:49:44.900
there and then it’s going to do the same

1074
00:49:43.4 –> 00:49:48.680
all the way through here it’s going to

1075
00:49:44.9 –> 00:49:50.690
be a 300 millimetre long signal and it’s

1076
00:49:48.68 –> 00:49:53.089
got to pass right through the system as

1077
00:49:50.69 –> 00:49:55.400
this signal passes along here the

1078
00:49:53.089 –> 00:49:58.670
leading edge of this signal is going to

Transcript for Introduction to Fiber Laser Marking (Cont…)

1079
00:49:55.4 –> 00:50:02.119
encounter the most number of excited

1080
00:49:58.67 –> 00:50:05.720
electrons ready to drop down and produce

1081
00:50:02.119 –> 00:50:08.089
a photon which will join this army so

1082
00:50:05.72 –> 00:50:11.779
the leading edge of this signal will

1083
00:50:08.089 –> 00:50:13.460
collect the most number of photons so

1084
00:50:11.779 –> 00:50:15.289
but the time this signal gets to the

1085
00:50:13.46 –> 00:50:17.059
other end here the signal is going to

1086
00:50:15.289 –> 00:50:23.809
come out the other end is likely to look

1087
00:50:17.059 –> 00:50:27.410
something like this it’s still one

1088
00:50:23.809 –> 00:50:29.750
nanosecond wide but the leading edge has

1089
00:50:27.41 –> 00:50:31.970
collected more photons than the trailing

1090
00:50:29.75 –> 00:50:34.309
edge of the signal and so that is how

1091
00:50:31.97 –> 00:50:36.710
that signal goes into here

1092
00:50:34.309 –> 00:50:37.940
and the chances are that what it’s going

1093
00:50:36.71 –> 00:50:40.099
to do is kind of come out the other end

1094
00:50:37.94 –> 00:50:42.200
very similar to that but maybe with a

1095
00:50:40.099 –> 00:50:45.289
little bit more trailing edge Distortion

1096
00:50:42.2 –> 00:50:47.869
here is the chart that I was given which

1097
00:50:45.289 –> 00:50:51.829
made no sense to me when I received it I

1098
00:50:47.869 –> 00:50:54.470
was told that hey if you run at 850

1099
00:50:51.829 –> 00:50:55.940
kilohertz with a 2 nanosecond signal

1100
00:50:54.47 –> 00:50:59.020
that’s when you’re going to develop

1101
00:50:55.94 –> 00:50:59.020
print our

1102
00:50:59.4 –> 00:51:05.109
so when I look at the other end of the

1103
00:51:01.779 –> 00:51:09.940
scale here which is 350 nanosecond

1104
00:51:05.109 –> 00:51:12.970
signal pulse that seems quite staggering

1105
00:51:09.94 –> 00:51:18.160
because when we started putting real

1106
00:51:12.97 –> 00:51:21.339
numbers to that 350 nanoseconds and we

1107
00:51:18.16 –> 00:51:24.369
know the speed of light causes 0.3 of a

1108
00:51:21.339 –> 00:51:26.859
meter per nanosecond that means that

1109
00:51:24.369 –> 00:51:30.700
signal is actually a hundred and five

1110
00:51:26.859 –> 00:51:33.460
meters long in other words I start the

1111
00:51:30.7 –> 00:51:36.670
signal off here and it’s actually coming

1112
00:51:33.46 –> 00:51:38.829
out and burning on the job before I’ve

1113
00:51:36.67 –> 00:51:41.470
actually finished the signal coming into

1114
00:51:38.829 –> 00:51:44.079
the end here because this is only 10

1115
00:51:41.47 –> 00:51:45.970
meters long now if I’ve got the physics

1116
00:51:44.079 –> 00:51:47.739
of that wrong perhaps somebody will tell

1117
00:51:45.97 –> 00:51:50.829
me but that’s the way that it looks to

1118
00:51:47.739 –> 00:51:52.869
me that’s how we can get these really

1119
00:51:50.829 –> 00:51:55.960
weird shaped pulses because the leading

1120
00:51:52.869 –> 00:51:58.059
edge passes through here so I’ve only

Transcript for Introduction to Fiber Laser Marking (Cont…)

1121
00:51:55.96 –> 00:52:05.140
got a signal which is sits which sits

1122
00:51:58.059 –> 00:52:08.109
there for 350 nanoseconds like this it’s

1123
00:52:05.14 –> 00:52:10.269
now a very long pulse but the trailing

1124
00:52:08.109 –> 00:52:16.359
edge of their pulse is going to look

1125
00:52:10.269 –> 00:52:18.269
like this because the tail end of the

1126
00:52:16.359 –> 00:52:22.680
pulse is going to collect a lot less

1127
00:52:18.269 –> 00:52:25.930
photons than the leading edge because I

1128
00:52:22.68 –> 00:52:28.269
presume that the path blazer is not

1129
00:52:25.93 –> 00:52:31.809
going to be working while the signals

1130
00:52:28.269 –> 00:52:34.119
working I don’t know I don’t know what

1131
00:52:31.809 –> 00:52:36.400
the mechanism is but this clearly

1132
00:52:34.119 –> 00:52:38.380
describes to me a mechanism by which we

1133
00:52:36.4 –> 00:52:41.410
can generate these strange-looking

1134
00:52:38.38 –> 00:52:45.039
pulses that come out of this signal

1135
00:52:41.41 –> 00:52:48.309
element here now I suspect that this

1136
00:52:45.039 –> 00:52:49.630
will be energized all the time but they

1137
00:52:48.309 –> 00:52:51.430
don’t know whether these will be in the

1138
00:52:49.63 –> 00:52:54.130
Joseph these are the sort of facts that

1139
00:52:51.43 –> 00:52:55.839
I can’t find anything about nobody out

1140
00:52:54.13 –> 00:52:57.910
there is telling me how this thing works

1141
00:52:55.839 –> 00:53:01.029
so I’m having to try and work it out

1142
00:52:57.91 –> 00:53:02.920
from yourself now maybe know that

1143
00:53:01.029 –> 00:53:04.359
somebody’s seen me struggling they might

1144
00:53:02.92 –> 00:53:06.400
be able to enlighten me and give me a

1145
00:53:04.359 –> 00:53:09.549
very very simple explanation as to how

1146
00:53:06.4 –> 00:53:10.750
this works but in the absence of anybody

1147
00:53:09.549 –> 00:53:13.210
else’s explanation

1148
00:53:10.75 –> 00:53:15.070
I’m happy to work with this as a model

1149
00:53:13.21 –> 00:53:16.780
the only thing that I can absolutely be

1150
00:53:15.07 –> 00:53:18.820
sure is I’m going to get a leading edge

1151
00:53:16.78 –> 00:53:22.800
pulse which is a lot higher than the

1152
00:53:18.82 –> 00:53:25.570
trailing edge pulse and that agrees with

1153
00:53:22.8 –> 00:53:28.599
several facts that I’ve already got this

1154
00:53:25.57 –> 00:53:30.820
is the 350 milliseconds which looks like

1155
00:53:28.599 –> 00:53:33.460
this it’s got a very long trailing edge

1156
00:53:30.82 –> 00:53:35.770
whereas in fact the tune in the second

1157
00:53:33.46 –> 00:53:38.619
pulse which is this one here has got a

1158
00:53:35.77 –> 00:53:40.869
very very short trailing edge when we

1159
00:53:38.619 –> 00:53:44.200
look across this graph typically we’re

1160
00:53:40.869 –> 00:53:46.960
talking about 12 kilowatts peak power

1161
00:53:44.2 –> 00:53:49.240
for most of these pulses and then we get

1162
00:53:46.96 –> 00:53:52.300
to this lower range which are about 8

1163
00:53:49.24 –> 00:53:54.520
kilowatts but over a much wider period

1164
00:53:52.3 –> 00:53:58.030
so one has to assume that we can

1165
00:53:54.52 –> 00:54:01.240
actually do more sustained damage with

Transcript for Introduction to Fiber Laser Marking (Cont…)

1166
00:53:58.03 –> 00:54:03.490
this range of pulses that we can with

1167
00:54:01.24 –> 00:54:07.030
these these are going to produce very

1168
00:54:03.49 –> 00:54:08.710
sharp deep pulses can I say there’s not

1169
00:54:07.03 –> 00:54:11.650
very much energy and there’s a lot of

1170
00:54:08.71 –> 00:54:13.240
power but not very much sustained energy

1171
00:54:11.65 –> 00:54:15.460
in there to do damage to the material

1172
00:54:13.24 –> 00:54:17.500
but that’s one of the subjects I’m going

1173
00:54:15.46 –> 00:54:19.480
to have to investigate how much damage

1174
00:54:17.5 –> 00:54:21.490
can I do to the material with each one

1175
00:54:19.48 –> 00:54:24.869
of these pulses now that I’ve begun to

1176
00:54:21.49 –> 00:54:27.880
understand this my list of numbers here

1177
00:54:24.869 –> 00:54:29.230
begins to make a little bit of sense so

1178
00:54:27.88 –> 00:54:32.740
let’s take a quick look at this 2

1179
00:54:29.23 –> 00:54:35.470
nanosecond pulse here what it means is

1180
00:54:32.74 –> 00:54:37.570
that inter if I’ve got 2 nanoseconds and

1181
00:54:35.47 –> 00:54:40.960
I’ve got an eight hundred and fifty

1182
00:54:37.57 –> 00:54:44.200
kilohertz maximum allowable frequency

1183
00:54:40.96 –> 00:54:50.520
that I can run at approximately that’s

1184
00:54:44.2 –> 00:54:53.740
roughly one microsecond for every cycle

1185
00:54:50.52 –> 00:54:56.589
approximately so that means that I’ve

1186
00:54:53.74 –> 00:55:00.010
got roughly a ratio of two nanoseconds

1187
00:54:56.589 –> 00:55:03.130
to a thousand nanoseconds which is

1188
00:55:00.01 –> 00:55:05.440
roughly 500 to 1 or in real terms let’s

1189
00:55:03.13 –> 00:55:07.930
go back to here and say that if I put a

1190
00:55:05.44 –> 00:55:11.740
two nanosecond pulse in there that means

1191
00:55:07.93 –> 00:55:14.710
I’ve got 998 nanoseconds in which to

1192
00:55:11.74 –> 00:55:17.380
recharge or rien vert the population in

1193
00:55:14.71 –> 00:55:18.609
here to make it fully charged again so

1194
00:55:17.38 –> 00:55:21.820
that I can understand

1195
00:55:18.609 –> 00:55:23.150
alright that’s why I must make sure that

1196
00:55:21.82 –> 00:55:27.210
I don’t exceed

1197
00:55:23.15 –> 00:55:30.090
850 kilohertz not it runs slower because

1198
00:55:27.21 –> 00:55:33.540
if I run at 500 kilohertz then there’s

1199
00:55:30.09 –> 00:55:35.160
even more time for the light to invert

1200
00:55:33.54 –> 00:55:38.010
that population and get full saturation

1201
00:55:35.16 –> 00:55:40.650
in there ready for the next pulse so I

1202
00:55:38.01 –> 00:55:43.080
can always run these numbers at smaller

1203
00:55:40.65 –> 00:55:45.780
values but I mustn’t run these numbers

1204
00:55:43.08 –> 00:55:48.090
at larger frequencies now in Lotus

1205
00:55:45.78 –> 00:55:49.980
installed the machine for me they

1206
00:55:48.09 –> 00:55:54.180
provided me with this very useful piece

1207
00:55:49.98 –> 00:55:56.940
of support documentation which basically

1208
00:55:54.18 –> 00:55:59.160
tells me understanding the differences

1209
00:55:56.94 –> 00:56:01.800
between q-switched and micro lases which

Transcript for Introduction to Fiber Laser Marking (Cont…)

1210
00:55:59.16 –> 00:56:03.960
is hopefully can be very interesting and

1211
00:56:01.8 –> 00:56:07.910
on the front page they give me this

1212
00:56:03.96 –> 00:56:11.250
diner if I had a physics doctor in

1213
00:56:07.91 –> 00:56:14.430
optoelectronics I might be able to

1214
00:56:11.25 –> 00:56:18.930
understand this but this is pretty

1215
00:56:14.43 –> 00:56:25.980
meaningless too I think most people meet

1216
00:56:18.93 –> 00:56:28.260
the wording used here hf f BG ydf these

1217
00:56:25.98 –> 00:56:30.510
are all acronyms which mean absolutely

1218
00:56:28.26 –> 00:56:33.540
nothing to me I mean I know that this

1219
00:56:30.51 –> 00:56:41.040
happens to be a a hyper ramen scattering

1220
00:56:33.54 –> 00:56:44.040
fiber Bragg grating Wow fantastic what

1221
00:56:41.04 –> 00:56:46.670
is it what does it mean we’ve got the

1222
00:56:44.04 –> 00:56:51.030
same thing here hello Raman scattering

1223
00:56:46.67 –> 00:56:53.430
fiber Bragg grating well technically

1224
00:56:51.03 –> 00:56:55.470
these two things here are the mirrors I

1225
00:56:53.43 –> 00:56:57.540
think I’ve described to you the break

1226
00:56:55.47 –> 00:56:59.030
grating well you need to go and have a

1227
00:56:57.54 –> 00:57:03.240
look up and see what that is

1228
00:56:59.03 –> 00:57:08.310
these are this Y D F stands for

1229
00:57:03.24 –> 00:57:13.650
ytterbium doped fiber okay it’s easy

1230
00:57:08.31 –> 00:57:17.490
when you know and this a o M it’s an

1231
00:57:13.65 –> 00:57:19.230
acoustic octo modulator what’s that well

1232
00:57:17.49 –> 00:57:23.450
that’s my piece of electronic cotton

1233
00:57:19.23 –> 00:57:26.880
wool my simplified drawings are that

1234
00:57:23.45 –> 00:57:28.770
exactly without all the frigging bits in

1235
00:57:26.88 –> 00:57:32.580
the same way that look this is a motor

1236
00:57:28.77 –> 00:57:35.610
system as described by presumably jpt

1237
00:57:32.58 –> 00:57:36.390
originally it there’s a lot more stuff

1238
00:57:35.61 –> 00:57:39.809
in here

1239
00:57:36.39 –> 00:57:41.460
deleting my simple diagram it’s called a

1240
00:57:39.809 –> 00:57:44.999
YB doped

1241
00:57:41.46 –> 00:57:47.369
DCF net what’s a DCF well it’s a

1242
00:57:44.999 –> 00:57:51.380
diffusion corrected fiber there’s a very

1243
00:57:47.369 –> 00:57:54.119
good site on on the web called photonics

1244
00:57:51.38 –> 00:57:56.880
encyclopedia you’ll find a lot of this

1245
00:57:54.119 –> 00:57:58.920
stuff defined in there but the problem

1246
00:57:56.88 –> 00:58:00.869
is you won’t understand most of the

Transcript for Introduction to Fiber Laser Marking (Cont…)

1247
00:57:58.92 –> 00:58:03.329
stuff that’s in there because it’s

1248
00:58:00.869 –> 00:58:05.789
written in Klingon for people that read

1249
00:58:03.329 –> 00:58:08.910
Klingon and I’m afraid I’m just a very

1250
00:58:05.789 –> 00:58:10.799
humble old-school engineer and most of

1251
00:58:08.91 –> 00:58:13.319
this stuff means nothing to me so I like

1252
00:58:10.799 –> 00:58:15.749
to reduce it back to the very basic

1253
00:58:13.319 –> 00:58:17.670
elements that I can understand and I

1254
00:58:15.749 –> 00:58:20.160
hope I’ve done the same thing for you

1255
00:58:17.67 –> 00:58:23.489
jpt claim all sorts of things for their

1256
00:58:20.16 –> 00:58:25.079
little bit of kit for the next phase I’m

1257
00:58:23.489 –> 00:58:27.359
going to be working with the machine to

1258
00:58:25.079 –> 00:58:30.329
see just how close I can get to some of

1259
00:58:27.359 –> 00:58:32.279
this stuff so I look forward to seeing

1260
00:58:30.329 –> 00:58:34.880
you in the next session thank you very

1261
00:58:32.279 –> 00:58:34.880
much for your time

Transcript for Introduction to Fiber Laser Marking