21 – Fiber Laser Machine – Bubble Marking Clear acrylic (46:12)

The Fiber Laser Learning Lab Series with Russ Sadler

In this Series, Lotus Laser have lent Russ a MOPA 20 watt fiber laser to “play with”. Although Russ has a moderate understanding of laser technology (his words) and how constant power glass tube systems work, the pulsing fiber laser machine is shrouded in a deeper mystery than the glass tube machine.

They have been designed for high speed marking and the technology has been well tried and proven. There are limited “tricks” that the pulsing laser technology can perform. You enter predefined parameters for each marking “trick” you wish the machine to deliver , then stand back in amazement. Most correspondents tell Russ that they have bought their machine direct from China and received a machine and EZCAD software, preloaded with a few default parameters. No other instructions beyond the EZCAD manual are forthcoming.

Russ states “I am neither a teacher or expert in this field so you join me in my learning adventure with the warning that I have a simple but inquisitive mind and will probably make mistakes on my way to discovering the truth. I WILL oversimplify and maybe distort the scientific detail in my quest to build a simple picture of why and how this technology works. I am not trying to reverse engineer anything, just to break through the seemingly impenetrable ‘techno cotton wool’ that surrounds this amazing piece of science.”


Contents

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This video is the last of the Fiber Laser Learning Lab Series. Why not try out one of our other video series such as:

The Tangerine Tiger Series where Russ has purchased a new 500 x 300mm, 50W laser machine from eBay with a view to modifying and upgrading it. In fact, he rips out the glass laser tube and high voltage power supply and replaces them with an RF laser source and PSU from Cloudray. Find out how the expensive RF laser source compares to a glass CO2 laser tube and prepare to get your hands dirty!

The Lightblade Learning Lab is a series of videos that Russ did for Thinklaser Limited based on using the Lightblade 4060 Laser Cutting and Engraving Machine. The Lightblade 4060 has a 400 x 600mm bed size and was supplied with a 60W EFR laser tube.

The Lightburn Software Series is probably the best generic laser cutting software available (I use it for almost all of my laser work). This series has tutorials, hints and tips as well as the occasional speed comparisons between it and RDWorks. My thanks to the team at Lightburn for allowing me to embed their videos.

The Top 10 Ranked RDWorks Learning Lab Videos

You may also wish to consider checking out The Concise RDWorks Learning Lab Series that condenses all of Russ’s work into an easy to follow encyclopaedia of laser knowledge.


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Fiber Laser Machine - Bubble Marking Clear Acrylic
Fiber Laser Machine – Bubble Marking Clear Acrylic

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Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic

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0:00welcome to another fibre laser learning lab um today we’re going to carry on with

0:06some stuff that we investigated a few sessions ago the strange effects of

0:14one micron light on various materials you may remember that i experimented with some glass

0:21um we’d already found out that for example that clear materials that we can see through um it appears

0:28that one micron light can see through here i’ve got a piece of clear acrylic

0:34it would appear that one micron light goes right through that and has no effect on the acrylic at all

0:39in the same way that has no effect on glass or on water whereas when we fire the one

0:45micron light that clear polycarbonate it definitely has an effect so it must

0:51all be down to the atomic and the molecular structure of the material itself when you fire the laser at glass and it

0:58passes right through the glass if you’ve got a piece of metal underneath the glass

1:03you vaporize the metal and you deposit the vapour onto the back of the glass fascinating

1:10process so one of the strange thoughts that i had was that can i do it on acrylic

1:18well the answer really is no because acrylic melts at 160 degrees c and it boils

1:23and vaporizes at 200 degrees c whereas vaporizing this copper

1:32is up in the over a thousand degrees c so i’m going to do some serious damage to the back surface of this acrylic

1:41hang about isn’t that what i want if i can fire the light through the

1:48acrylic bounce it off the surface of the copper or stainless steel or aluminium or any

1:54other metal i choose to use does that mean to say that i can actually engrave on the back

2:00of this i don’t want a vapor deposit any metal onto it i just want to create enough

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

2:06heat reflected off of the metal to damage the surface of the material

2:13it should be possible so let’s go and experiment bear in mind some of the other lessons that we’ve learned about

2:18this machine and we’ve been warned that we shouldn’t actually try and work below the focal point or we

2:24shouldn’t try and reflect metals back up into the lens so i’ve got this work pushed across to

2:31the side so that it’s not reflecting directly back into the lens but if it’s going to do anything it’s going to reflect off somewhere else

2:37into space so the first thing i’m going to do is set the part height to 1.5 millimeters which is the thickness

2:44of the copper so we’re actually going to reflect off of the surface of the copper because

2:49that’s the plan

3:02the answer is not a lot we’ve managed to mark the copper but we’ve

3:10not generated enough heat for long enough to damage the acrylic

3:20well again it’s done a great job of marking the oh look we’ve got

3:26something on our acrylic

3:33not a lot because look i can wipe it off so it must be basically almost smoke but let’s go down a little

3:40bit lower to 500 with our speed put more pulses in per unit of time

3:48that’s something rather interesting happening there hopefully you did as well you noticed

3:54some speckles and some sparks as it was engraving now

4:00we’ve got a really strange effect starting to happen now we have not really well we’ve marked the

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

4:07back but i don’t know whether you can catch

4:12in catch it in the light there just right something is happening inside the

4:19material because it isn’t just a mark on the back we’ve got when i catch in the light just right i

4:26can see some little sparkles in there we’ll take the speed down to 250 now

4:33and look at all that look at all that’s happening inside there

4:38now what’s happening there something weird has taken place look i’ve got a whole load of bubbles or

4:45something taking place inside the material normally we wouldn’t be able to mark this at all let’s try a different sort

4:54of material underneath here is a back reflector

4:59let’s try some aluminium won’t change the settings

5:07i’ve still got the focus basically down on this surface here

5:22so we’re busy exploding the material we must be producing bubbles inside

5:28there we must be vaporizing the material somehow inside the acrylic

5:34and it’s expanding and as you heard it pop as it exploded i certainly don’t appear to be succeeding at

5:42burning the surface of this and heating the surface of the acrylic

5:47i’ve got no idea what i am doing but hey that’s not unusual for me

5:54now because i’ve got an air gap under there now i’m going to produce the surface marking

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

6:01and i’m going to get quite high temperature ionized gas which is coming off the surface

6:08producing a that’s what that white flame is you know it’s it’s ionized gas if i put the material straight down

6:15onto the surface i’m preventing any oxygen from getting to the surface and so i’m basically preventing ionization taking

6:22place

6:29well we get a lot more noise we also get less explosive

6:36burning and what we’re picking up now is all these bubbles from underneath

6:42which is this surface here now that gives the impression that we’re doing something with a reflection

6:48now let’s try the same thing with copper what copper does as opposed to

7:00aluminium

7:06hmm we’re getting some sort of effect which is coming up from a reflected image i think the first

7:13thing we’ll do is see if we can control the damage that we’re getting in there can we stop it being quite as

7:19violent as this because look some of it is explosive and burning out so let’s put

7:24the speed back up to 500 so we’re putting less power in so let’s

7:29go back from 500 back to say 300.

7:40fuel taking place from the underneath here and we’ve got a little bit of damage on the underneath surface

7:50but as you can see the the burning the bubbles are taking place low down

7:57can i change the position of those bubbles by changing the focus at the moment the focus is set onto this

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

8:04surface here and it’s reflecting back up into this

8:10material what happens if i put the focus on the top surface i wonder let’s come right up

8:16to the top so instead of 1.5 for my part depth it’ll be 1.5

8:22plus 1.5 which is 3 plus 9.5 which is 12.5

8:28so we’ll keep the settings exactly the same but we’ll change the part we’ll change the focus

8:3412.5 to see if this is somehow related to focal depth or reflections or

8:42i’ve got no idea what it is at the moment because we shouldn’t be achieving anything inside that material

8:56when we look at it from the side there look it’s now passing fairly uniformly all through the

9:02material we increase the power by putting the

9:08speed down let’s go back to 200.

9:15see we’re getting burning at the surface now

9:21we’re definitely getting a lot of bubbles and they’re not going completely all the way

9:27through they’re from the surface down to maybe six or seven millimeters into the

9:33material that’s where the density of it is i don’t know whether you can see that look can you see this

9:40this strange pattern here look that’s a that’s a shear plane that’s an explosion plane within the

9:46material it’s actually opened up a void so we’re definitely producing gas

9:52inside the material at the moment i’ve got a pulse width of 250 nanoseconds which

9:59is quite a lot of power per pulse let’s back that off to something like maybe

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

10:04100.

10:12how you saw that shear plane open up just there at the moment the scan lines are .05

10:20we could increase the power by five times if i decrease the

10:27interval to 0.01

10:35aha we’ve got nothing coming out of the

10:43surface at the top now we’ve got some very nice bubbles in there in fact it’s

10:50most of the energy most of the bubbles are in the center so if i take a nice

10:56clean version so there’s no confusion and we’ll repeat that test

11:09we’ve got very little blowing out the top this time

11:14most of those sparks are down the inside but most of the energy is in the center

11:23at the moment i’ve got the focus set to 12.5 let me lift the focus let me lift the

11:28material thickness which will effectively pull the focal point up above the material i’m going to take it up to

11:3615 15 millimeters

11:51well it certainly has an effect i think you can clearly see there look it’s brought it right up to the top

11:58surface so whatever is happening it’s got something to do with the focus

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

12:06question is is that the focus combined with a reflection how much is the reflection

12:14playing on this uh how can we test that

12:21very simple we have a piece of paper now we know

12:27that this stuff doesn’t pass through paper so this will begin to tell us hopefully

12:36what’s going on

12:49and the answer is it’s got nothing to do with the reflection by the look of it because we’ve got no change in the

12:54result i mean we shouldn’t be able to mark this material at all because the light is passing

13:00through it so we have to ask the question how is it possible

13:06to mark the material

13:21i’m going to change that part height from 15 which is about three

13:27millimeters above the material at the moment i’m going to go right up to 20 millimeters and see what happens here we

13:34go i can see a few little flickers right

13:40down on the bottom surface now

13:46whatever it is is all down to focus let’s go the other way and drop it

13:52halfway into the material

13:57and we’re now getting an effect of some sort

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

14:04and whereas my thoughts were that it was to do with reflections and interference between

14:12beams the fact that there is no reflection there

14:19tells me it’s all to do with the focus but how can that be what is happening

14:29so after a few more experiments i’ve got what i think is a pretty good

14:36set of parameters it still doesn’t explain what we’ve got here but

14:44i’m going to run this and then we’re going to probably have a look at it under the microscope to see if we can

14:51first of all see what these so-called bubbles are they must be bubbles you’ve got to be evaporating

14:57little teeny weeny chunks of material and turning them into gas

15:04the longer pulse is actually not as good as the shorter

15:10pulse 22nd 20 nanoseconds

15:16115. yeah we’ve got a lot more sparkle in there now

15:38this one’s a shorter pulse time and it’s beginning to look quite a lot

15:44better and it’s more uniform throughout

15:50let’s try 13 nanoseconds

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

16:01it’s pretty uniform throughout look it’s gone all the way through the material there

16:06pretty but it just doesn’t look

16:13i mean it’s 3d which makes it interesting i would like to see it so it’s obvious

16:20on the surface like one of the others that we produced and we did that by pulling the focus

16:28up a little bit so at the moment it’s set to eight millimeters which is three

16:34millimeters to there and five

16:42five millimeters away from 9.5 which means it’s 4.5 into the material

16:50right well let’s give this a try shall we this is 1500 millimeters a second

16:5675 kilohertz 45 nanosecond pulse and we’ve got a point zero one interval

17:04between the line scans so we’re 4.5 into the material

17:19[Music] now as you can see that looks pretty uniform although we’ve got we’ve got

17:24some density at the top we’ve got quite a lot happening down below let’s see what sort of surface

17:29well you see that’s getting better that that’s getting because we’ve got it closer to the surface

17:36a little bit more visible on the surface itself

17:42when i put some led lights behind it look

17:52it’s looking pretty good

17:58okay so here we are in the office with my low-powered usb microscope because my big microscope is

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

18:04just too powerful to see what’s going on now it’s it’s interesting to note that what i’ve got here

18:10is a piece of pink paper in the background with some pink strands in it as you can see and you can see that they are nicely in

18:17focus the background so i’m focused through the material onto the background but look what happens when i

18:23draw the material away the background has gone out of focus so

18:30the material is already having an effect on the light

18:37and the way it’s focused so there’s some strange effects going on inside this material even with visible light

18:46now when we start looking at the bubbles that i’ve produced what we’re looking at now are the

18:52bubbles that right down on the bottom surface let’s just move across a little bit and

18:58see ah there we go now that’s not untypical of what i’m finding

19:04if we take a look here you’ll see that we’ve got like a little white blob that’s a bubble

19:11but what it’s done it’s exploded inside the material and look it’s produced this like a halo

19:18it’s almost like when i look inside this material look you’ve got all these different

19:23oval shapes look there’s one there that looks like satin look you know with its rings and all of these

19:30look like little mini universes they’re all laid at different angles and they’re all fracture planes you’ve

19:36got a little teeny weeny spot of gas that’s appeared in the middle

19:42and it’s then exploded out pushed out and managed to shear a plane around it

19:49and that’s what these are all looking like so the acrylic melts at 160 degrees c

19:57it then turns into vapor like steam at 200 degrees c but unlike steam

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

20:05it is a volatile chemical it’s got hydrocarbons in it whatever

20:12heating is taking place in there has also heated up the vapor and turned that vapor into

20:18like a material it’s almost oxidized it and turned it into a material

20:24and there’s lots of these little teeny weeny black spots around in here so we’ve got like a double chemical

20:29reaction taking place some of them are low temperature and they just produce a little teeny weeny white bubble

20:36with a fracture plane and some of you are these very dark spots where are these little spikes

20:44of energy coming from they’re spikes of energy which are doing damage to a

20:49material that would normally allow the light to pass through so we

20:54must be experiencing some sort of interference pattern between the light waves

21:00which is causing some increase in energy intensity and this

21:07shows us what happens to light as it passes through a transparent material like glass or

21:15acrylic so the light approaching the transparent material is at a fixed frequency and

21:22it hits the material and slows down now the frequency does not change

21:29because the frequency is the color of the light you can say well yeah i can see the frequency has slowed down well

21:36no what’s happened is the wavelength has shortened if you count the number of pulses

21:41passing by a single point you’ll find that there’s just as many

21:46peaks passing the point on the left and the right as there are passing any point within

21:52the glass we’ve got more peaks passing a point

21:57in the same period of time so so within the material we’ve got a lot more light waves

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

22:05but because the color of light is defined by its frequency and not by its wavelength

22:13then the light has remained unchanged in terms of its color

22:19i’m trying to make sense of why and how you can get splashes of power

22:26inside the material you do get a crowding effect of waves inside the material

22:34now the other thing that we have to take into account is the fact that the beam is not

22:41parallel we’re busy focusing the beam down so by very very definition

22:48the waves that are running down this beam are not running parallel to each other

22:54and as i’ve mentioned maybe on a couple of occasions before i’m a little bit puzzled because if the

23:00waves are traveling different distances then they are basically traveling at the

23:06same speed because as we’ve seen from the previous diagram the waves go in at one speed

23:12slow down and then they come out at the same speed so they’re both traveling these waves

23:18are both traveling at the same speed but technically they’re traveling different distances because they’re on

23:23different legs of the triangle so they therefore must get out of phase

23:30the problem with things getting out of phase is you get something called super position

23:39the waves although they’re coming from the same light source and they’re at the

23:44same frequency they’re not running perfectly together and when you get

23:49superposition of waves according to wave theory you get interference now let’s just have

23:56a quick look at another diagram that i’ve knocked up quickly and here we can see two waves

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

24:02running towards a focal point they’re gradually getting closer and closer and closer and they are

24:08the same frequency right but if they are the same frequency this wave

24:15and this wave they can exist in the same space without interfering with each

24:20other so in this case look we’ve got this wave running at a very slight angle

24:26to the other wave and when they cross over they will cross over and carry on as

24:32normal so they start off as two waves and they finish up as two waves but at the point where they physically

24:38occupy the same space something strange happens and they

24:44either become additive as in this case because we’ve got two waves that are the same frequency and the same

24:51amplitude the amplitudes add so we get double the amplitude at just a very small

24:59section where the waves try to occupy the same space now because these are coming down at a

25:04very gentle angle i mean i’ve only drawn one super

25:09plus wave there but it could well be that there are two or three or four which are gradually building to a plus

25:15and then back again and so we we don’t just get one we get a pulse of several waves but those waves the

25:23energy at that point is much more than the single wave energy whereas

25:30if they get out of phase like this and they stay out of phase then you never get this plus we’re

25:36always getting minuses okay so this is what happens when they’re in phase

25:43which is probably a very rare situation but here’s what happens when they’re out of phase

25:48okay the same applies here so you get no plus pulses so it’s only on this one special situation where you

25:55could get some very high energy pulses

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

26:00now this is the only thing that i can think of that fits the random sparkle

26:09that we’ve got in our material so we know at this point here

26:14we’ve got relatively low energy density we’re not able to do a lot of damage and

26:20it’s only when we start compressing the waves together that we increase the intensity of the light

26:26we’re not absolutely we’re not changing the amplitude of the light we’re just changing the the density of

26:32the closeness of the waves effectively putting more energy into one specific point more

26:39intensity so if we want to detune the intensity at this point here we’ve

26:47got several ways of doing it one of them is to change the amplitude of these waves and we do that

26:53with the power so we can reduce the power which means we get smaller waves which

26:58means we should get less big pulses because they won’t double up as much

27:04so that’s one way that we can decrease the power the other way that we can decrease the power is to defocus

27:12in other words we can move a long way above or a long way below the focal point and then we shall finish up with if you

27:19like waves like this where they’re quite a long way apart and they’re not going to interfere with each other and even if they interfere with each other

27:25they’re so weak at that point because they’re not crushed together that they won’t actually do any damage

27:32that we cannot get any high spikes of energy we’re going to go back to the machine if we can find

27:38the the point at which we get the maximum density of this interface

27:44the maximum density of our bubbles in the center of the material okay we

27:50should be able to detune with reducing the power

27:56to make the bubbles less so we leave the focus as it is and we

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

28:01should be able to tune tune the bubbles out we should be able to lift the focus up and lift the focus

28:09down and bring this point closer and further away from the top or the bottom of the material

28:15it’s the only mechanism that i can envisage which will excite the molecules within

28:21the material when light collides normally it’s the surface atoms and molecules

28:26that get vibrated to a higher temperature well here we’re not vibrating surface

28:32molecules to a higher temperature we’re vibrating molecules within the structure

28:37to a higher temperature so something very strange is taking place to cause little pulses

28:43of energy within the material itself to vibrate the molecules up to a high enough level

28:50where they vaporize and even within the vapor we might even be burning the vapor and

28:57turning it into a carbonyl type material it’s a fascinating idea i’ve looked around a

29:03lot and i can find nothing by way of research to explain what’s going on i’ve got a one

29:11inch block of acrylic and i’m going to stand it on edge this time so that we can see the

29:17penetration into the material rather that try and guess what’s happening through the thickness of the material

29:28you can immediately see that actually

29:40it looks as though the densest part of that is probably around about

29:45three or four millimeters down into the material so perhaps the first thing i should do

29:52is raise the height from 25 to 28 millimeters in other words i’ll lift the focus

29:58three millimeters out of the material to see whether or not it’ll drag the pattern upwards

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

30:05this one is a frequency of 75 with a 45 nanosecond pulse

30:10we’re using 100 power at 1500 millimeters a second and we’re now three millimeters above

30:18the work with the focal point [Music]

30:28and it actually looks quite nice on the surface as well doesn’t it

30:34so now i’ll go the other way and we’ll go three millimeters into the material

30:50and yes yes yes as you can see we’ve dropped it down into the material

30:57there’s no doubt it’s focus related so the one at the bottom was three

31:03millimeters high and the one at the top here is three millimeters low so this time we’ll have a go at reducing

31:11the power we’ve got a fixed pulse width of 45

31:16and the last time we did this we had just a little bit of crackle and pop on the surface

31:22so we reduce the power now to 80 percent it should reduce the density of the

31:28bubble it should reduce the density of the bubbles and also the risk of it going snap

31:34crackle and pop [Music]

31:43well that’s pretty amazing isn’t it for just a small change of power 20 percent

31:51[Applause] we’ve virtually lost it [Music]

31:57we’ll put the power back up to a hundred percent

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

32:04running slower puts more pulses into the job so let’s reduce it from fifteen hundred

32:10to a thousand and now we probably will expect to find

32:16more bubbles or more sheer planes and more crackling and popping

32:32well we’re running slower and it probably looks as though we’ve got a greater density

32:37without actually causing too much more physical damage yeah

32:44i mean it’s down below the surface

32:52[Music] so let’s leave it at a thousand and raise the part height again in other

32:57words we’ll take it three millimeters out above the surface to try and bring the pattern right back

33:04onto the surface

33:14[Music] now although we’ve taken it up to the surface

33:19we haven’t actually caused too much more damage in fact there’s less density

33:26there which is surprising i would have thought there’d have been more density there so we get more bubbles in there by

33:34probably then closing up the gap between the lines

33:41so we’re on a thousand speed hundred percent power frequency 75 pulse width 45 and

33:48line spacing 5 microns and we got a focus height of 28

33:55three millimeters above the surface

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

34:08now we’re cooking really cooking

34:16look at all that stuff going up in the air that’s gas i presume which is igniting their vapors that are

34:23igniting we’ve just burst out the top there with melted acrylic look

34:30so now we’re at eight microns line spacing

34:36[Music]

34:47that’s not bad but we did get a bit of uh popping and crackling didn’t we i tell you what i’m going to do i’m

34:53going to push the speed from i’m going to leave it where it is 0.08 where we got our crackling and popping

34:58and we’re going to push the speed up instead to two thousand from a thousand

35:07so we’ve doubled the speed and we’ve really lost most of our bubbles so here we are with

35:1330 millimeters above which is five millimeters above the surface we’ve still got our 45

35:19nanosecond pulse 800 millimeters a second and 100 power and a 0.01 line spacing

35:38i don’t think there’s any doubt about it now something to do with the focal point but

35:44we’ve got nothing that i would consider on the fro on the top there to be text it’s not

35:49readable text it’s not sufficiently dense enough so there’s our initial

35:55settings with the focus on the surface and it clearly shows that there’s something happening

36:02what three four millimeters below the focal point that’s where all this

36:08problem is occurring it’s not occurring before the focal point

36:16and we can prove that and we’ll see what happens when we push it down to say five

36:22millimeters into the material so we’ll go down to 20

36:38millimeters

36:48[Music] okay with those self-time settings now

36:54we’ll turn the job over and we’ll see what happens at 20

37:01millimeters do we lose the pattern because the

37:07energy is being absorbed before it gets to the focal point

37:12or is it going to drop the pattern down by five millimeters theoretically this

37:19material is transparent to one micron light so dropping the beam

37:25down by five millimeters should have no effect on the beam itself

37:30and our pattern should drop down by five millimeters

37:40[Music]

37:48well it certainly looks as though it might have done we’ve got some other slightly higher

37:55density patterns starting to happen just across the top there so let’s drop

38:01it another five millimeters and see what happens so the focus is now 10 millimeters down into the material

38:19[Music] you can see where it bubbles is our bubbles

38:29now bubbles is now about there that’s pretty interesting isn’t it it’s

38:35dropped it right the way down look we’ve lost it we’re no longer at the surface

38:42roughly where my thumbnail is is where the focal point is so that’s damage

38:49above the focal point so if i lift that up by about three

38:56millimeters it should bring that bubbles back onto the surface [Music]

39:10and there we are we’ve got our bubbles virtually back onto the surface

39:15but that line is where the focal point is

39:20and i think you can see it looks as though we’ve got another

39:27pattern building below the focal point as well as the one above the focal point

39:34so when i raise the focal point up to the top on this one i’ve got my bubbles here which obviously

39:42this pattern here so whatever’s happening is above and below the focal point

39:48it’s not at the focal point it hasn’t really proved the point about

39:54the wave theory idea of superposition and the addition or the extra power

Transcript of Fiber Laser Machine – Bubble Marking Clear Acrylic (Cont…)

40:01for a material that shouldn’t mark we’ve been able to market

40:07we’ve been able to create a problem inside there and we’ve got control of it now

40:14whether this is interference caused by colliding light waves adding together to increase

40:21the power at specific spots and of course it will be totally random

40:27because every pulse will be different which is why we’ve got a range there in

40:33fact we’ve got two ranges one above and one below the focus now we push one of these down to 15

40:41and we found our bubble was sitting just across there

40:47so now the focus is only five millimeters above this base [Music]

41:02how weird how weird is that that’s not

41:10building up from the top downwards all of a sudden is building up from the bottom upwards

41:18how’s that is that internal reflection off the bottom face of that material

41:27[Music] i’ll tell you what i’m going to do i’m going to try

41:3325 millimeters i’m going to focus directly on this piece of paper

41:50and much as we expected originally i don’t think we’ve got anything there have we

41:56[Music] [Applause] it doesn’t look like we’ve got anything

42:02there does that mean to say the energy has gone right the way through that block

42:08with no obstruction we have a piece of stainless steel there which will mark

42:15so if the light energy is passing right through that block it will mark that stainless steel so

42:21we’re just saying change the part height to one millimeter

42:31[Music]

42:37oh we’ve got a few little sparkles in here look we’ve got a few little sparkles at the

42:42bottom and we’ve got some energy that went through [Music]

42:50but let’s just see what the energy is by running the same test again without

42:59the acrylic in the way

43:12[Music] well that is interesting isn’t it

43:19that means that acrylic is not that

43:24transparent put enough of it in the way and it will absorb the energy

43:33so therefore i think we’re beginning to prove yes that at certain focal points within the

43:41acrylic we are creating little bundles or bursts of energy

43:48that are able to damage internally the acrylic now if you make the acrylic thin enough

43:55it will pass right through but make it thick enough and it will

44:00absorb the energy now the other thing that shows clearly

44:06is that we’ve been able to produce a nice gold finish on stainless steel that’s not the first

44:11time we’ve done that is it looking through the clear face of this perspect it’s much easier

44:18to see this little universe of spiral galaxies almost

44:24look every one of these has got a little teeny weeny bubble in the center little gas bubble

44:29which has caused these to produce all these little shear planes that go in lots of different directions

44:35so there is no uniformity about these and they’re not really bubbles the light seems to be catching

44:41like the rings around saturn it’s it’s it’s the shear planes that are picking

44:46up the light and making it look like bubbles so we started off trying to mark the acrylic

44:53by a reaction a burning reaction process we failed miserably at that but

45:01succeeded at something else that we didn’t really expect to find which is this

45:06bubble effect within the acrylic so i think the proposal that i made

45:12earlier about light wave interference patterns is not disproven

45:20but it looks credible is this of any use well i think it could

45:27be of use if you’re making trophies and things you know it could be quite an interesting trophy and especially

45:33if you can edge light it it’s certainly no good for photo replication work

45:38because the dots are so randomly scattered you’ve got no control of them but for text work you could make some

45:46quite nice text trophies maybe for instance i could imagine a very nice clock made with this because the letters would

45:52stand out well especially if you edge light it i’m only here exploring what’s possible

45:58i’m not attempting to utilize this in any way at all it’s just an interesting phenomenon that we’ve

46:04discovered about acrylic i think we’ll stop there and say thank you very much for your time and your patience and um

46:10i’ll catch up with you in the next session

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