04 – Fiber Laser Colour Marking (25:47)

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, pulsing fiber laser marking machines are shrouded in a deeper mystery than the glass tube machines. So let’s learn all about Fiber Laser Colour Marking.

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.

Fiber Laser Colour Marking: Examples of Various Coloured Markings
Fiber Laser Colour Marking: Examples of Various Coloured Markings

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.”

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Transcript for Fiber Laser Colour Marking

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0:00well welcome to another fiber laser

0:02learning lab as I promised you last time

0:05we’re going to look into one of the what

0:09I would call tricks of this type of

0:11laser machine which is a motor fiber

0:15laser machine now I’m told that you

0:18cannot perform this trick with a

0:20q-switch laser and certainly can’t

0:22perform it with a constant wave laser so

0:25we’re going to look into the secrets

0:27behind this trick as I will call it that

0:31this machine can perform to see if we

0:35can understand what the mechanism is and

0:38whether or not you might be able to do

0:41it with the q-switch laser now I suspect

0:42that many people ahead of me have tried

0:44to do it on a q-switched laser or even

0:46on a constant power laser like that but

0:48I think you’ll get to understand that I

0:50don’t accept that the round world is the

0:52best wheel for instance a square wheel

0:54it’s got some great properties you don’t

0:57need a handbrake in your car and it

1:00discourages theft so I’m gonna go out

1:03and explore all the possibilities

1:05although we want to get to a conclusion

1:07on this subject

1:08I’m afraid the conclusion will not be in

1:10this or any session soon because I can’t

1:14foresee that as I start progressing

1:17through this I shall get pulled off into

1:19all sorts of different side directions

1:21because I need to understand various

1:23other features that will go to finish up

1:26building the final picture so let’s get

1:30started now here I’ve got a piece of

1:34very thin stainless steel it’s

1:35point-five of a millimeter thick and

1:37it’s got a nice shiny surface to it and

1:40just here we’ve got blowing

1:44throw them behind there first of all

1:48you’ll see the metal distorting

1:51[Music]

1:55and then hopefully if I can control on

1:57the temperature right don’t get it too

1:59close

2:00I want it happen slowly can you see the

Transcript for Fiber Laser Colour Marking (Cont…)

2:03way the color is changing on the surface

2:05there are now hold it a little bit

2:07closer and keep it there

2:13[Music]

2:18now you can see look we’ve got it so hot

2:21is glowing red-hot

2:27if you watch carefully we’ll see that

2:28the colors are growing around the

2:32outside

2:34about those color since I was a very

2:37very young engineer because that was one

2:39of the first things they teach you when

2:40you’re in the training school how to

2:42harden metal using these colors as what

2:45they call tempering colors now these are

2:48basically colors of oxide that are

2:51formed when you heat metal up but

2:54they’re not colors in the sense that you

2:56normally see colors now when we look at

2:59that red fire extinguisher there we see

3:03it’s red because we’ve got white

3:06daylight shining on it and white light

3:12is composed of all the colors of the

3:14rainbow but basically what’s happening

3:18here is all the colors that are not red

3:21are being absorbed by the paint pigment

3:26that’s on the outside of that container

3:28and it’s only the red that’s being

3:31reflected like a mirror back at us so we

3:35normally see color by what I would class

3:38is subtractive absorption we only see

3:42the colors that are reflected off the

3:43surface we don’t see the colors that

3:45have been absorbed by the surface of the

3:47material now these are always nice clean

3:50crisp clear colors that we see so when

3:53we look at these colors here they’re not

3:55they’re nothing like normal absorption

3:59colors because these are created in a

Transcript for Fiber Laser Colour Marking (Cont…)

4:02completely different way but you can

4:05never get a pure rate a pure blue or

4:08appear green from this method of

4:11producing colors and this is the method

4:14that the mopey laser uses to produce

4:17colors it’s this technique here of

4:19oxidation on the surface of stainless

4:23steel particularly it can be done as I

4:25understand it on titanium I can’t prove

4:27on titanium because I don’t have any no

4:30in daylight out here virtually however I

4:33hold this whichever angle I hold this at

4:36we’ve got a nice mix of colors there are

4:39no pure colors there there are just

4:41these mixture of hmm interesting colors

4:45sort of

4:47and bright teal blue and golden yellow

4:51and a honey color now look if I twist

4:54this what we’re looking at there is an

4:58image of daylight from outside and

5:02that’s the image from inside under

5:04artificial LED light these are not real

5:07colors these are strange colors that are

5:10caused by some very interesting

5:13phenomena of light now here is a sample

5:16test piece given to me by Lotus later to

5:19show me what the Mopa type of laser can

5:22do the q-switch laser cannot do produce

5:26all these lovely colors look at that

5:28lovely green there and in daylight hello

5:33where’s the green gun we have all the

5:36colors gone so provided we get the light

5:43in the right direction we can have the

5:47colors so here we’ve got under our LED

5:51light and if I get the angle of the

5:53light right maybe some of the colors

5:56well you can just about get the green

5:58they’re provided look I provided those

Transcript for Fiber Laser Colour Marking (Cont…)

6:00shine the light on it right I can get

6:02the green to show otherwise it’s not

6:05green at all although this is one of the

6:07big selling points that they point out

6:10to you for a mobile Acer hmm so first

6:15off let’s go and see how these pseudo or

6:17false colors are produced well we’re

6:20gonna start off with the electromagnetic

6:22spectrum

6:22courtesy of Penn State College of earth

6:25and mineral sciences which owns you

6:27which is where I found this very nice

6:29diagram running from cosmic rays very

6:32very short wavelength through the

6:34ultraviolet then the bit that we can see

6:38and then the infrared where we’re

6:40working normally we work with our ten

6:42point six somewhere here but now we’re

6:44working pretty close to the visible

6:47spectrum this is only 750 nanometers and

6:51we are at about 1060 so we’re not much

6:56further up the scale than the visible

6:59red end of the spectrum but my real

7:01point of showing you this drawing is you

7:04can see that we’ve got a visible

7:06sensitivity in our eyes between 350

7:11nanometer wavelength light up to 750

7:15nanometer wavelength light and you can

7:16see the way in which the color spectrum

7:18changes now the colors that we’ve been

7:23seeing up to now are really probably not

7:26going to be found on this scale because

7:29they’re not pure colors now you’ll

7:33recall this image of me heating up the

7:35back side of a piece of stainless steel

7:39and here we’ve overheated it to such an

7:43extent that we’ve made it red red hot

7:47you’ll notice that the spectrum of

7:50colors that we’re creating are always on

7:54the outside of this area I mean it’s an

7:57indication very much like the the energy

Transcript for Fiber Laser Colour Marking (Cont…)

8:00density in the laser beam it’s probably

8:03following some sort of Gaussian

8:04distribution where we’ve got very little

8:07heat on the outside here because you’ve

8:10got conductivity of the material you’ve

8:13got a large radiation area down to air

8:15temperature normal air temperature and

8:18so the heat within this material is very

8:22quickly dissipating and there’s it’ll be

8:24warm out here but not hot now what sort

8:29of temperatures are we talking about

8:30here that’s really what we’re interested

8:32in what about the red hotness to start

8:35with there’s a scale of color which has

8:40been devised and I would guess that we

8:43not right in the middle there that

8:46possibly could be classed as bright

8:48cherry red around this area here it’s

8:51red to dull red so possibly we might be

8:56up at 800 degrees C in the middle here

9:00let’s see what happens when we take the

9:02heat away

9:05the answer is that so

9:08that was the boundary almost about red

9:11hotness and within that boundary a very

9:14high heat

9:15look when we look at the oxide that’s

9:18been left behind on the surface it’s

9:21this tail blue going to a darker blue

9:25there and then merging to a sort of a

9:27move and then a brown and then a light

9:30straw

9:30well there are temperature definitions

9:32for each one of these colors so for

9:34instance the outside edge they’re called

9:36faint yellow which is right out here 176

9:40degrees C light straw which is this

9:44secondary phase in here 205 degrees C

9:49it’s only 29 degrees C hotter but it

9:53changes from faint yellow to light straw

9:55and then we’ve got this area here which

9:57is classed as light blue blue and then

Transcript for Fiber Laser Colour Marking (Cont…)

10:00all this section in the middle here has

10:02classed as grey blue and we’re talking

10:05about 371 degrees C so let’s just put

10:10that on the chart there that’s somewhere

10:12around about there 371 degrees they’re

10:19interesting because look we’ve heated

10:21that all the way up to 800 degrees C and

10:23500 degrees C in the middle there as it

10:26cools down to 371 degrees C it creates

10:29this color so but the thing I want to

10:31emphasize here is we’ve created these

10:33colors with a blow lamp a very crude

10:36instrument but it does require these

10:41temperatures here up to 371 degrees C to

10:46produce these colors now as I explained

10:49to in the previous session temperature

10:51is only a function of the vibrational

10:55level of the material so 371 is not very

11:02hot the question is how do we control it

11:08how do we make it happen

11:10do we need long pulses I mean it takes

11:13takes a lot of energy to put that much

11:15into the surface now we might not be

11:20able to see any accurate colors on here

11:22but what we can see is that we’ve got

11:24very accurate control of the shapes so

11:26we haven’t got a lot of overheating and

11:29heat flow away from our marking area now

11:34in the previous session we talked about

11:37this material which is our iminium if

11:39you remember I said to you oxygen and

11:42metal will automatically form a an oxide

11:46layer on the surface it’s incredibly

11:48thin and it’s completely transparent as

11:50you can see here because this looks like

11:52raw aluminium but I know that it’s not

11:56that there is an oxide layer on that

11:58surface there now this shiny surface on

Transcript for Fiber Laser Colour Marking (Cont…)

12:04the stainless steel is even more

12:06sensitive to the advances of oxygen

12:10let’s just have a quick look and I’ll

12:12explain why stainless steel has got a

12:16very high chromium content 18 to 20

12:20percent oxygen and chromium are

12:22absolutely in love with each other so

12:25this has got a very thin layer of oxide

12:29on the surface it’s much thicker than

12:30the aluminium it’s probably something in

12:33the region of about two nanometers thick

12:35and you know what that is maybe six

12:38eight ten atoms thick and literally as

12:43soon as you damage the surface within a

12:46few nano seconds so I’m told it will

12:49heal itself which is why this material

12:52is stainless its self-healing and it’s

12:55continuously protecting the surface with

12:58this chromium oxide this very thin layer

13:00of chrome oxide on the surface as you

13:02can see it is transparent because we can

13:06see through to the shiny material

13:07underneath and that leads us to a

13:11phenomenon that you have seen many times

13:15before I give you the soap bubble or an

13:19oil film on a puddle yeah I think this

13:21is a very interesting composite

13:23that’s not real because if you take a

13:25look here we’ve got these three trees

13:27here and we’ve got these three trees

13:30here which are one of the same and

13:31they’ve just rotated the image to give

13:33you a nice general impression but what

13:35you have got here is all the typical

13:37colors that we’re seeing in here but

13:41these have had no heat in them at all so

13:45where do those colors come from now you

13:48might want to go and do your own

13:50research on this but I’m very quickly

13:53going to go through the thin film

13:56interference theory which is what we’re

Transcript for Fiber Laser Colour Marking (Cont…)

14:00talking about it’s a phenomenon

14:02associated with light and light waves

14:05very very crudely we have a light wave

14:08that comes in and strikes the surface of

14:12the film that’s on the top there and

14:16then we’ve got a certain film thickness

14:18here let’s call it T I’m not going to

14:21get too technical about this you can go

14:23and do your own reading on this subject

14:25thin film interference but generally not

14:28always but generally there is something

14:30called a phase reversal as the light

14:33hits the surface so it comes on for

14:36example let’s just call these +100 is

14:42obviously these point here and minus one

14:43we’ve got a complete mirror image of

14:46what came in so that’s that’s the first

14:49thing that happens we get this light

14:51coming in and reflected off the surface

14:54and then we’ve got this thin film here

14:57and at last as we can see we can see

15:00through that thin film to the material

15:02underneath so the light travels in to

15:05that thin film okay so it’s only one or

15:07two nanometers thick but that means the

15:11light is traveling further the colour

15:14remains the same but the speed of the

15:16light actually slows down and as it

15:18slows down so it changes its angle and

15:21instead of coming through and hitting

15:24the bottom just here as you might expect

15:26it hits the bottom here and then it

15:29bounces off the bottom again probably

15:31where the phase reversal comes out at

15:33the same

15:33as the reflection these light beams are

15:36no longer in phase look the top of this

15:39one is now no longer in line with the

15:42top of that one so the color that came

15:45in and the color that came out will be

15:49the same but it might not be as intense

15:52so you can get something called additive

15:55or destructive interference between

15:58these two beams now I’ve drawn them a

Transcript for Fiber Laser Colour Marking (Cont…)

16:00long way apart they’re not going to be a

16:02long way apart so the simple story that

16:04I want to get over to you here as we

16:05send one wave in and we get two waves

16:10out one off the top surface and one off

16:12the bottom surface and those waves

16:13interfere with each other and I’m now

16:17going to show you the effect of those

16:18two waves interfering with each other

16:20now I’m indebted to the guys that

16:22created this piece of software because

16:25it makes my life a lot easier in trying

16:27to explain light waves to you now waves

16:31are waves whether they’re light or sound

16:33they all look the same so what we should

16:36be doing is hearing color rather than

16:39seeing color in this demonstration now

16:43the annoying buzz in the background is a

16:45color because this is what a color looks

16:48like now the only difference between

16:50colors is this

16:55the length of the waves now that’s the

17:00read long wavelength frequency there’s

17:04there’s one wave on the screen that’s a

17:07long wave now if we double its frequency

17:11and we put two waves on the screen

17:14that’s a different color but even here

17:17it’s a different color but you can hear

17:18that it’s a lovely smooth color now that

17:22relates to all those colors that you see

17:24on the color chart the color range that

17:28our eyes can see

17:30every pure color has got this lovely

17:33sine wave shape to it now when we get

17:37two different colored lights mixing

17:39together like this

17:42they produce a single wave which is

17:45completely different it’s the sum of all

17:48these bits and pieces here

17:51so if we look here we’re going to get

17:53addition of the red and the blue and

17:55here we’re going to get subtraction of

17:57the red from the blue so we’re going to

Transcript for Fiber Laser Colour Marking (Cont…)

18:00get around a strange waveform and if we

18:02use this little slide here it’ll show us

18:04what happens when we mix the two

18:07together now in the thin-film picture I

18:11showed you that the first wave came out

18:13let’s call it the blue wave and then the

18:16second wave came out at a different

18:18point in a different phase so there was

18:20a shift between the two waves and that

18:23shift basically is going to cause a an

18:28interference pattern between the two now

18:31it’s not going to cause a color

18:32interference because they’re both the

18:34same color what it’s actually going to

18:37do if we listen very carefully

18:42at that point there they are 180 degrees

18:45out of phase the pluses of one wave

18:49cancel the minuses of another wave and

18:52the net result as we like move on this

18:54slider and have a look is zero so we

18:57have no color at all now we’ve got

18:59blackness so the phase shift and this is

19:06called destructive interference actually

19:08cancels the light out and as we get

19:12further and further interphase we get

19:15back to the original intensity of light

19:18so we’ve got phase shift to think about

19:21and we’ve got this mixing of different

19:24types of waves now there’s a further

19:27mixing effect which takes place and

19:29that’s when we get several colors

19:31nowhere we start changing the frequency

19:33of these

19:35[Music]

19:45now say what they net out us

19:54see that’s a really weird signal and

19:57that’s the sort of light you can hear

19:59that it’s not a pure tone and you can

Transcript for Fiber Laser Colour Marking (Cont…)

20:02see that it’s not a pure sine-wave it

20:04sounds strange waveform which gives

20:07these weird colors that we’re talking

20:09about it’s an interference effect

20:15and that interference effect changes as

20:18the thickness of the film changes

20:21because as the film thickness changes so

20:24the relationship between the wave going

20:26in and the wave coming out changes but

20:30of course we’re not just talking about a

20:31single color wave but much more complex

20:35than that we’ve got thousands of light

20:38waves of different frequencies entering

20:41and thousands of light waves of

20:43different frequencies exiting so we get

20:45a massive combination of all these

20:47frequencies and colors that are inter

20:49playing with each other hence these very

20:52strange

20:53non-standard colors I will call them

20:55they’re not colors that you’re likely to

20:57find find in the standard color chart

21:00when you look at that straight on now

21:03everything looks pretty dull and black

21:05but if I move the camera and move this

21:10into the light so you’re still looking

21:11at it straight on at a certain angle of

21:14incidence of light the colors appear so

21:19you’re still looking at it straight on

21:20but the light angle into the surface has

21:24changed so we’ve got light coming in

21:27here and we’ve got your eye there and

21:33depending on the relative difference

21:36between these two angles depends on the

21:37color that you see because it depends on

21:40the distance of T the thickness of the

21:43film and the lower the angle the longer

21:48the distance the more the interference

21:52between the two so all these little

21:56black patches and black things here when

21:58you catch them in the light right you

Transcript for Fiber Laser Colour Marking (Cont…)

22:00can make them either disappear or turn

22:02into pale gray now I suspect that some

22:06of these have been done with scans

22:08across this way and some of them been

22:10done with scans across that way so that

22:12depending on how the light catches them

22:13maybe they do or they don’t disappear so

22:18somewhat none of these colors on here

22:20are pigment colors they’re all

22:22refraction colors

22:24caused by this thin film interference

22:27effect yes we used a lot of heat to

22:32create these colors but we didn’t use

22:35any heat there we have to draw the

22:38conclusion that the only thing that the

22:40heat is doing is changing the thickness

22:43of this film so I’m afraid there is no

22:46magic pen that this machine has which

22:49paints different colors on the surface

22:51of stainless steel it doesn’t even

22:53require heat to produce these colors it

22:57produces it needs a thin transparent

23:00film we’re going to have to manipulate

23:03the thickness of this film to produce

23:05these non pigment colors but when we

23:10come to modifying the film thickness of

23:13stainless steel here it appears that we

23:18need to have certain temperatures to

23:20create these colors I’m not sure that we

23:23have to locally heat up to these

23:26temperatures to produce these colors it

23:28could well be that if we stimulate the

23:30surface we might be able to promote

23:32growth in stages

23:35sometimes you can’t crack the problem

23:37with logic and in this particular

23:39instance I felt hey it’s very simple if

23:43we fire the motor laser at this surface

23:45here the Mopa has got the ability to

23:49dispense very very small precise amounts

23:52of light energy and that light energy

23:56will be stimulating the molecules in

Transcript for Fiber Laser Colour Marking (Cont…)

24:00here to higher and higher temperatures

24:02and those higher temperatures just local

24:04temperatures in this area here are going

24:07to if you like percolate out into the

24:10background material and heat the

24:12background material up by conduction

24:15okay before it dissipates away to

24:18nothing but having hated the background

24:20material up

24:21that’s an improved environment for the

24:25combination of oxygen and chromium

24:28because adding heat to any chemical

24:31reaction speeds it up but hey the film

24:35is chromium oxide so it’s already got

24:37its oxygen

24:38so I’m a little bit puzzled as back as

24:41to whether or not we’re going to be able

24:44to promote growth on to the surface of

24:46the thickness or whether we’re going to

24:49be trying to promote growth into the

24:52material maybe just heating this little

24:55area up throws everything into confusion

24:57and we can actually get below the film I

25:01say maybe I told you before I’m not a

25:03chemist and I’m not a physicist so I

25:05don’t understand exactly how this

25:07mechanism works but what I do know is

25:09we’re going to have to change the film

25:11thickness to change the interference

25:13patterns between the incoming and the

25:15outgoing light so in the next session

25:18we’re going to get dragged off onto one

25:20of these tangents that I mentioned

25:21earlier and we’re going to have to

25:23investigate the actual power of pulses

25:26that we have on this machine we’re gonna

25:29have to look at ways in which we might

25:31be able to find a strategy for

25:34thickening this film I could go and ask

25:37Lotus laser but I’m not going to so on

25:41that stubborn note I’ll say cheerio to

25:44you and we’ll catch up in the next

25:45session

Transcript for Fiber Laser Colour Marking

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