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.

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
To be completed soon.
Video Resource Files
There are no more resource files associated with this video.
External Resource Links
There are no more external resource links associated with this video.
Transcript for Fiber Laser Colour Marking
Click the “Show More” button to reveal the transcript, and use your browsers Find function to search for specific sections of interest.
0:00well welcome to another fiber laser learning lab
0:02as 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 mopa fiber laser machine
0:15now 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 mopa 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 mopa laser 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 mopa 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