How Fiber Lasers Work: Epic Materials & the Laser Beam Guide

00:01

well welcome to another session of the

00:04

fiber Laser Learning Lab so that first

00:07

session was a long session because I

00:09

really wanted to try and cram in as much

00:12

information as possible about the

00:14

machine we managed to find out and

00:17

understand how a laser actually works

00:20

and then we’ve applied it to the the

00:24

constant output gas laser and then we

00:28

began to understand how a fiber laser

00:30

works and how the q-switch laser is

00:34

different from this one which is a mocha

00:37

laser so I feel fairly confident that

00:40

I’ve got a pretty good understanding of

00:43

how these two fiber laser systems work

00:46

now I can’t test this as a q-switched

00:49

laser because it isn’t I might be able

00:52

to simulate a q-switched laser with some

00:54

of the forces but I don’t know because I

00:57

haven’t used this machine before now the

01:00

most that I used this machine was last

01:02

time when I guess that some parameters

01:06

to run this very simple little test here

01:09

I used something like a 60 nano second

01:13

pulse and some other speed and frequency

01:18

parameters which I guessed at and well

01:22

we got a result what we proved last time

01:26

was that different materials react

01:28

differently to different frequencies of

01:31

light because we’ve managed to produce

01:35

that surface mark there on the constant

01:39

output glass tube laser which runs at

01:42

ten point six microns wavelength whereas

01:45

when we did the second mark there I

01:49

place the glass directly on top now

01:53

after we’d finished filming I thought

01:54

that was really a little bit cheating

01:57

because we did make a very small mark on

Transcript for how fiber lasers work (Cont…)

02:00

the underside of the glass but then I

02:04

realized that that mark on the underside

02:05

of the glass was really a reflection or

02:07

reaction of the material that we were

02:10

producing when we produced this white

02:12

mark

02:13

so subsequent to that what I did was

02:17

this I put some two mill spacers down

02:20

and I produced the third mark no

02:24

different than the second mark except

02:26

there was absolutely zero effect on the

02:31

glass and it just proves that that the

02:34

light beam was passing cleanly through

02:36

the glass ignoring the glass and all the

02:38

power was going into doing damage to the

02:41

surface of this black anodized material

02:45

so today’s technical session is all

02:48

going to be about the light and the

02:51

properties of light and how that light

02:53

can actually damage this surface and

02:56

then we’re going to talk about this

02:58

material and this surface and work out

03:01

how the relationship between the light

03:03

and the chemistry of this surface

03:04

creates this result now we’re here we’ve

03:08

got a data sheet supplied by jpt and

03:12

there’s several interesting pieces of

03:15

information on here which was useful for

03:17

us well I did mention to you I think in

03:19

the previous session the claim for this

03:21

particular machine is 0.06 spot where

03:25

there is 0.063

03:27

spot size and it says here that the

03:32

focal length is 254 millimetres 254 10

03:36

inches so that agrees with what I’ve

03:39

seen on this machine and it says that

03:41

it’s got a working depth of field and

03:43

here we can see look the depth of field

03:45

which is the useful part of the beam

03:48

where the focus is remaining good enough

03:52

to produce a spot size of 0.6 0.063

03:57

there’s another interesting piece of

03:59

information here which they’ve given us

Transcript for how fiber lasers work (Cont…)

04:00

which tends to possibly confuse this

04:04

true focal point and that’s this piece

04:10

of information here they’re telling me

04:12

this this beam which comes out of the

04:15

laser is a what they call an M Squared

04:19

of 1.3 now M Squared is a

04:25

definition which is used to define the

04:27

quality of a laser beam one is a perfect

04:31

Gaussian distribution an M 1.3 varies

04:36

very slightly away from a Gaussian

04:38

distribution now I’ve talked a lot about

04:40

light and Gaussian distribution within

04:42

the beam in my other glass tube laser

04:45

series but for those people that haven’t

04:48

been looking at that because they’re not

04:49

interested in you know cheap Chinese

04:52

tubes I will just quickly go through

04:54

what this means and just here I’ve got a

04:59

little torch which is a cloaks

05:01

equivalent to the laser beam it’s got a

05:03

single LED in the end of it now when I

05:06

shine this light on this surface you’ll

05:07

see that it’s got a very bright

05:09

high-intensity whiteness in the middle

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and then the intensity of the beam

05:13

gradually gets weaker and weaker as it

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gets to the outside well we can see that

05:20

now on this white light but we can’t sit

05:24

on the laser beam because the laser beam

05:26

is invisible and this is a typical

05:28

normal distribution curve with the glass

05:31

tube plates are running a ten point six

05:33

micron wavelength it’s very easy to see

05:36

the damage and the shape of the power

05:39

distribution within the beam I call it

05:41

power distribution that’s really wrong

05:44

it’s a light intensity distribution

05:47

within the beam and if we take a look

05:49

here the light intensity when it reacts

05:52

with the acrylic has actually evaporated

05:57

away a shape which is equivalent to this

Transcript for how fiber lasers work (Cont…)

06:02

normal distribution curve let’s assume

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that a beam was six millimetres diameter

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well here we’ve got one to three

06:10

millimetres on one side of Centre and

06:12

three millimetres on the other side of

06:14

Centre so within the central two

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millimetres of the beam we’ve got 68

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percent of the total light intensity and

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then when we drop out to the next

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millimetre we’ve got fourteen percent

06:26

fourteen percent and then right at the

06:28

outside we’ve got next to nothing two

06:30

percent two percent we may have a six

06:32

millimetre beam going into the lens

06:34

we’ve really only got four millimetres

06:38

which has got any power and in reality

06:40

we’ve only got about two millimeters

06:43

with any significant power but what

06:46

you’ve got to remember is the focal

06:48

point the spot comprises the whole of

06:53

this energy distribution so that means

06:56

when we’ve got a point oh six diameter

06:59

spot size for this beam it’s probably

07:05

only about 0.02 which has got the real

07:07

damage power in it so the next thing

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that we have to understand is the nature

07:14

of light and how this very very special

07:19

light the laser beam which if you

07:21

remember we’re turning raindrops into a

07:23

tsunami wave so that everything is

07:26

acting together and we’re pushing them

07:27

down this pipe and concentrating them

07:30

and making them even more dangerous than

07:32

the tsunami wave so when you go outside

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on a sunny day the first thing that you

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feel is heat on your face for example

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you think guides a bit warm out here

07:43

today where do you think that heat comes

07:45

from yeah I know it’s coming from the

07:48

Sun but how does it arrive at your face

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it can’t be the same effect as when you

07:54

stand by a fire or a radiator the Sun is

07:58

90 odd million miles away and I know

Transcript for how fiber lasers work (Cont…)

08:01

it’s a very very bright bonfire the heat

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does not travel through a vacuum you

08:08

probably know that intuitively because

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how many of you have actually used or

08:13

daily use a vacuum flask or one of these

08:17

Yeti cups or something like that if

08:19

there are no molecules and there’s a

08:21

vacuum inside there heat will not travel

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so this Sun that’s a long way away from

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us and separated by a huge amount of

08:30

vacuum cannot send its heat directly to

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us the only way that the heat gets to us

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is in the form of light the light waves

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are traveling from the Sun and can

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travel in a vacuum and when they arrive

08:47

at your face

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what they do they actually make the

08:53

molecules in your skin vibrate hang on

08:58

let’s go back to the first session

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remember what I said

09:01

temperature vibration of molecules and

09:06

atoms the more they vibrate the hotter

09:09

they are so what’s actually happening is

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sunlight one particular frequency of it

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called infrared is actually hitting your

09:19

skin so there’s an energy transfer

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between the light waves and the

09:26

molecules in your skin and you’re

09:27

stimulating the molecules in your skin

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to vibrate faster and as they vibrate

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faster they feel hotter because they are

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getting hotter magnitude of vibration

09:39

equals temperature remember so the more

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you can vibrate something the hotter it

09:44

gets now that’s a fundamental principle

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that you must not forget because that is

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how your laser beam is damaging the

09:51

surface of any material that it comes

09:54

into contact with it’s the same

09:56

principle as a rock falling out of the

09:59

sky that rock is completely harmless it

Transcript for how fiber lasers work (Cont…)

10:04

has energy it will do no damage until it

10:08

hits something and then there will be an

10:10

energy transfer from the rock to

10:14

whatever it hits ok that’s a physical

10:18

thing that you can imagine but it’s

10:21

exactly the same principle when we’re

10:23

talking about light the light travels

10:25

until it hits something and then you get

10:28

an energy transfer of the light energy

10:30

into the surface of whatever it hits and

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although this might look like a solid

10:36

piece of material in reality the atoms

10:38

in this glass are probably there’s only

10:43

maybe I don’t know 1% solidity in there

10:46

it feels like solid to us but in terms

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of light the light is the light at that

10:52

particular frequency is going right the

10:54

way through and there is not enough

10:56

energy in the photons to excite or do

10:59

any damage to this glass that

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surface damage is caused when the when

11:05

the light energy hits the surface and

11:07

changes into stimulating heat which

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raises the temperature of whatever this

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black surface is hopefully you’ve now

11:16

got the idea there is no heat in the

11:18

light beam itself the light beam is

11:21

stimulating their material molecules to

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vibrate faster and it’s the molecules

11:26

the vibration in the molecules that

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determines their temperature so this

11:31

invisible light firing at the surface of

11:33

water is ten point six microns

11:35

wavelength but what it’s going to do

11:37

it’s going to stimulate the molecules

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it’s going to excite them up to a level

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where their temperature gets above a

11:45

hundred degrees C and we know what

11:47

happens at 100 degrees C steam it

11:51

evaporates so let me just press the

11:54

pulse button and show you what happens

11:55

when we fire the laser at water okay

Transcript for how fiber lasers work (Cont…)

12:01

let’s have a look whether I produced a

12:04

white spot under thee here none of the

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energy has gone through the water the

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energy coming from the light beam has

12:15

been converted into molecular vibration

12:20

and the molecular vibration has got

12:23

greater and greater and greater to a

12:24

point where the water can no longer

12:26

remain as a liquid

12:28

and it changes its state if we put a

12:32

piece of acrylic underneath here the

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Acrylic is basically exactly the same as

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water I know it doesn’t look like water

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but trust me this is equivalent to ice

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we’ve got a solid material here which is

12:47

solid at room temperature you heat this

12:49

up to 160 degrees C and it turns into a

12:53

liquid you heat it up to 200 degrees C

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and it vaporizes just like steam so

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that’s the way that this material reacts

13:05

to ten point six micron wavelength light

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because it’s able to convert the energy

13:10

of the light

13:12

into molecular motion now keep stressing

13:15

this mechanism because it is a very very

13:18

important principle that you must always

13:20

carry with you when you see you’re doing

13:22

damage to material I’m going to leave

13:24

the guard open so that we can witness

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this and I’m going to fire one micron

13:29

wavelength light into water through

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glass and onto a piece of black anodized

13:35

aluminium it’s the same program that I

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used to produce this stuff in the

13:40

background here

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job done I didn’t see any steam

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[Applause]

13:51

most of the light has gone through and

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some of the energy has actually

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stimulated the surface of the black

13:58

anodized aluminium when we passed the

14:00

light through glass

Transcript for how fiber lasers work (Cont…)

14:02

it had no effect at all so it’s just the

14:05

water that’s caused this attenuation of

14:08

this energy absorption of the light

14:10

energy and very little of the energy has

14:13

got through to stimulate the molecules

14:16

in the surface of that black anodized

14:19

aluminium that’s an interesting

14:22

experiment now I’m going to be using

14:25

black anodized aluminium with this one

14:29

micron laser because I think this is

14:31

about as close as I can get to a a very

14:35

good what I call a telltale material

14:38

that tells me what’s going on with this

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light with the ten point six micron

14:43

laser acrylic was my favorite material

14:46

because you saw what it does it

14:49

evaporates the material like it

14:51

evaporates water the energy is converted

14:53

into evaporation now made with most

14:56

other materials that that can be damaged

14:59

by the ten point six micron wavelength

15:02

the molecules are heating up to a point

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where they can no longer exist together

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in the form that they are when water is

15:10

stimulated it heats up to its critical

15:15

temperature of 100 degrees C and then it

15:17

changes into another form it’s still

15:20

water but it changes into a gaseous form

15:23

called steam when you stimulate an

15:27

organic material like paper with ten

15:29

point six micron wavelength light it

15:32

it’s molecules vibrate faster and faster

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and faster until it can no longer remain

15:40

as paper now just give you an example

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here look I’m adding energy in the form

15:47

of a an external heat source I know you

15:50

could look at it and say yeah I just I

15:52

saw you add heat to it that’s why it

15:54

burnt for those of you that have not

15:56

seen

15:58

constant laser beam before coming across

Transcript for how fiber lasers work (Cont…)

16:02

here in space is that invisible beam and

16:06

it goes in there hits a mirror bounces

16:08

down and gets focused through there so

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at this point we’ve got an unfocused

16:13

later bee and a piece of paper now I

16:19

didn’t start that fire with a flame I

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started that fire with light so

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something started off as paper it got

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excited by light hitting its molecules

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the molecules vibrated faster and faster

16:39

and faster until a point where they

16:41

could not exist together the independent

16:45

atoms that formed the molecule decided

16:48

to break away from the partnership form

16:50

a relationship with other chemicals

16:52

other elements that were around like

16:55

carbon and oxygen

16:58

and they produced this ash material this

17:01

is a chemical change that took place

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because of stimulation it’s a different

17:08

process to the stew the process of state

17:12

change where it changes state from water

17:15

to steam so we’ve got these two distinct

17:17

processes that can take place when we

17:20

fire light at a material so here that

17:25

paper that’s no longer paper

17:27

it’s basically shaking itself to pieces

17:30

what are we looking at here to create

17:32

this sort of change is it evaporation

17:36

process is it a chemical change well to

17:43

investigate that we need to understand

17:45

what this material is this black

17:48

anodized aluminium here is a piece of

17:51

raw aluminium now what we’re looking at

17:54

there is looks like a piece of metal in

17:59

reality on that surface there there is a

Transcript for how fiber lasers work (Cont…)

18:04

very very very thin film of oxide now

18:08

oxygen is a very very volatile material

18:10

it’s a gas that we breathe but hey God

18:16

didn’t trust us with it he only gave us

18:18

20% because it was so dangerous and he

18:20

gave us 80% nitrogen but that oxygen

18:24

combines very easily with metals but as

18:28

soon as it combines with the metal the

18:30

reaction stops so we get a very very

18:33

very thin film of aluminium oxide on the

18:37

surface of this material that looks

18:39

exactly like raw aluminium the raw

18:43

aluminium has just underneath the

18:45

surface there we’re talking about one or

18:47

two atoms thick you will normally

18:49

recognize aluminium oxide it’s a white

18:53

substance that they use in grinding

18:56

wheels and in sandpaper okay so it’s not

19:02

white there but that’s only the glue

19:04

that’s holding it to the background to

19:05

the paper so the process of anodizing

19:09

this material starts off

19:11

by converting this surface here this

19:14

metallic surface into aluminium oxide

19:17

which is a nonmetal and as I’ve just

19:22

shown you with the grinding wheel this

19:25

aluminium oxide is a crystalline

19:28

material and it forms little crystals

19:29

all over the surface micro crystals now

19:32

this structure here on the surface

19:35

that’s been created by a an electrolytic

19:38

process is incredibly thin still it’s

19:43

still only somewhere in the region of

19:45

three maybe five microns maximum

19:48

thickness five millionths of a meter

19:51

that here is about five times thicker

19:53

than the aluminium oxide layer that’s on

19:56

the surface of an anodized aluminium but

19:59

of course in real terms that probably

Transcript for how fiber lasers work (Cont…)

20:01

means it’s around about I don’t know two

20:04

three four hundred atoms thick so it’s

20:08

actually in atomic terms a very thick

20:10

layer but even so there are still

20:13

crystal structure there which has got

20:16

voids between them but then we’ve got

20:19

we’ve got the outside world which might

20:21

be full of chemicals it could be liquid

20:24

water it could be acid it could be

20:26

anything that’s corrosive could leach

20:29

through those small voids and attack the

20:33

aluminium that’s underneath having put

20:36

the hard oxide layer on the surface they

20:39

then coat it and fill in the gaps with

20:44

some special chemical a sealant but

20:48

often before they put the sealant on it

20:50

can go through a secondary process and

20:53

this becomes then the third process the

20:56

second process being to dip this white

21:01

aluminium oxide some of the pores

21:04

between the crystal structure has been

21:06

filled with a black dye and in this

21:09

example here it’s been filled with a red

21:12

dye but this is still anodized aluminium

21:16

the process of anodizing is the process

21:20

of converting the material from raw

21:22

aluminium into an aluminium oxide

21:25

and then everything else on top of that

21:27

is to preserve the integrity on the

21:30

surface we’ve got the sealant and once

21:33

that gets heated up to say 200 degrees C

21:36

it will evaporate so that then exposes

21:39

the water-based black dye that’s in

21:43

between the crystal structure to become

21:46

excited although water and glass might

21:49

look transparent to us at these other

21:51

wavelengths of light glass and water

21:54

react differently I keep saying the

21:57

light has heated the material up no the

22:00

light has stimulated the material heat

Transcript for how fiber lasers work (Cont…)

22:02

itself up that’s the critical thing that

22:04

you must bear in mind the aluminium

22:06

oxide can be stimulated it has got to be

22:10

stimulated to about 2,000 degrees C

22:14

before turn to liquid and 3,000 degrees

22:18

C before it’ll vaporize off so if we can

22:21

see the gray aluminium through there we

22:24

know that we’ve achieved over 3,000

22:27

degrees C now I know these concepts

22:30

these numbers they sound incredible it’s

22:32

it’s almost like science fiction but

22:34

these are not things that I’m surmising

22:37

these are absolute facts that you can

22:40

chant check for yourself

22:42

so that’s why I should be using this as

22:45

a tell tale material when I come to look

22:48

at the various power capabilities of

22:52

various pulses and frequencies when

22:54

we’re testing this machine later on well

22:58

I think that’s enough of my silly

22:59

pictures and stupid science today thank

23:03

you for your time and patience and this

23:05

is going to lead on to another fairly

23:08

serious physics lesson when we look at

23:11

this subject next time Calem arcing of

23:15

stainless steel