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 about Fiber Laser Color 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.”
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Transcript for The Search for Colour
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00:00
well welcome to another fiber laser learning lab
00:02
to start off with I’m
00:06
sitting here in my office because it’s
00:08
nice and warm we’ve got quite a lot to
00:10
talk about technically and look at some
00:11
results before we go out and jump on the
00:14
machine and do one or two quick tests
00:17
it’s a very unexcited machine and really
00:21
what we’ve got to do is try and
00:22
understand what it’s doing because it
00:26
does a lot without looking very
00:28
spectacular now what we’ve got here is
00:32
the results of the laser matrix test that I
00:36
carried out last time and what I’ve done
00:38
I’ve broken these down into frequencies
00:40
every one of these patterns on here
00:42
relates to this maximum peak power chart
00:45
that I was given we run from one known a
00:48
second to 350 nanoseconds and there are
00:50
16 of these patterns and we tested all
00:53
these at frequencies which do not
00:55
necessarily tally with this chart as we
00:58
look through these results I will make a
01:00
note roughly of where these maximum
01:02
power numbers tally up with my chart so
01:05
we’ve got nothing that tallies on this
01:07
front sheet here because we’re running
01:09
too fast over a thousand at a thousand
01:12
kilohertz these two you might look like
01:14
black-and-white images trust me these
01:16
are coloured pictures and if we look
01:20
very carefully we can pick up the yellow
01:22
hue that we saw on the screen when we
01:26
looked at some of these results last
01:27
time and there’s definitely yellow hue
01:29
there and there on my results there
01:32
might even be a hint down here at this
01:34
one which is rather strange so when we
01:37
move on now to 900 kilohertz again we’ve
01:43
got these definite yellow hues up here
01:46
at 2 and 4 nanoseconds even though we’re
01:49
not at the frequency for peak power now
01:51
the frequency for peak power is
01:53
appearing on this page it’s supposed to
01:56
be 850 but here we’ve got 800 so we’ve
01:59
got more than enough time to promote all
Transcript for the Search for Fiber Laser Color Marking (Cont…)
02:02
the electrons up to their excited state
02:05
before we put the pulse through and then
02:07
we put them when we put on out to now in
02:09
a second pulse through that’s when we’re
02:11
supposed to get our max
02:12
and we can definitely see here again
02:15
look we’ve got a yellow hue to here and
02:17
a yellow here even at four seconds for
02:19
nanoseconds so yeah we’ve got a
02:23
relationship at the moment where we see
02:26
peak power yellow we’re still seeing
02:30
peak power yellow at two nanoseconds
02:32
even at 700 kilohertz which is not one
02:35
of the preferred numbers 600 here we are
02:38
again definite yellow pattern 500 now
02:45
500 is the peak power for 4 nanoseconds
02:49
and sure enough look at four nanoseconds
02:52
we’ve definitely got that yellow hue and
02:54
maybe at five nanoseconds at six no no
02:57
seconds as well now we come to 400
03:00
kilohertz and there’s not supposed to be
03:03
much happening there at fall killer 400
03:06
kilohertz but look which still got here
03:10
there is a very there is a very dark
03:13
pattern there and it is quite yellow
03:15
here we’ve got a definite yellow pattern
03:18
and some of these here are yellow as
03:21
well so it looks as though we’ve got
03:24
quite a lot of power in this region here
03:27
even at 400 kilohertz and now we drop
03:30
down to 300 kilohertz where we’re
03:32
supposed to come across peak power for 6
03:34
nanoseconds and sure enough look there
03:37
it is bright yellow along with the one
03:40
above it at 4 nanoseconds and even the
03:42
one below at 8 nanoseconds has got a
03:44
brown a yellow hue to it as well and
03:46
even 13 in a second so we’ve got power
03:50
in this region here and here we are at 2
03:53
kilohertz where we’re supposed to
03:55
encounter the max power for 8
03:56
nanoseconds and sure enough there it is
03:58
look yellow there’s yellow at 6
Transcript for the Search for Fiber Laser Color Marking (Cont…)
04:01
nanoseconds but not much else down this
04:04
chart then this one was a little bit of
04:06
a puzzle because we’re supposed to come
04:07
across peak power here for 13 and 20
04:12
nanoseconds but these don’t look
04:14
particularly yellow now between 13 and
04:18
100 nanoseconds will looks as though
04:20
we’re beginning to develop this broader
04:25
d part of the pulse up to now 2 4 6 8
04:29
these have been very sharp peaky poses
04:33
so let’s just see what happens 2:30
04:35
we’ve got no distinct yellowness there
04:38
and here we are again look there’s lots
04:40
of these max powers that fall into this
04:42
category here and really when we look at
04:46
these none of them are really very
04:48
yellow they’ve lost that punch let’s
04:51
call it that that probably still got
04:53
quite a lot of power in them but they
04:55
don’t any longer burn the material and
04:58
then the rest of them which are hundred
05:01
and fifty up to 350 150 up to 350 all of
05:06
them occur on this page here and if we
05:09
take a look it’s rather interesting that
05:11
first of all they’re all lines which is
05:13
rather strange we’ve lost our pattern
05:15
but all these lines have got a slight
05:18
yellow hint to them so we’ve got I think
05:22
heat coming from a different direction
05:24
we’ve got sustained heat this time as
05:28
opposed to peak heat so I think when we
05:34
look at these lower pulses we’ve got to
05:36
consider that we’ve got a different way
05:38
in which we’re heating up the material
05:41
now that’s as low technically as I
05:44
should have gone but of course I went
05:46
lower than that and I’ve gone right the
05:49
way down to 5 kilohertz where basically
05:52
I’ve got rubbish results it’s a bit
05:55
expected because I’ve dropped off the
05:56
bottom of I’ve dropped off the bottom of
05:58
their chart there and serves me right so
06:01
there are interesting correlations in
06:03
those results to these patterns and
06:05
pulse Peaks
06:07
which we will be able to use and refer
06:09
to as we discovered last time one of the
06:13
most important things is try to work out
06:17
how we’re going to get heat down into a
06:19
specific spot now look here’s what we’re
06:23
trying to decode what’s going on here
06:26
and if you remember in the last session
06:30
I did mention to you that even though
06:32
the hole of this center section here
06:34
which finishes up as a blue went
06:37
red-hot
06:38
up at 800 900 degrees see it settled
06:42
back down to this blue when it got to
06:46
something like about 300 degrees C so
06:50
regardless of how high the temperature
06:52
went the oxide layer formed at a certain
06:56
temperature where I suspect the oxide
07:01
layer had reached a maximum thickness
07:03
because regardless of how hot we made it
07:05
we still got blue so the interpretation
07:09
of that is because these are refraction
07:12
colors coming off of the under neath and
07:15
you can see that even though it’s blue
07:19
we can see the image of that little
07:23
pointer on the surface underneath there
07:25
so this blue color is completely
07:29
transparent so our goal is to try and
07:33
find a way of thickening this oxide
07:38
layer that’s just here which is fully
07:40
transparent to a different thickness
07:44
that gives us these colors now as I said
07:49
it does look as though we’ve got a
07:50
maximum thickness we can make it up too
07:52
which gives us this blue and everything
07:55
else in between
07:56
now this clear layer that we’ve got here
07:59
is only somewhere in the region of about
Transcript for the Search for Fiber Laser Color Marking (Cont…)
08:01
two nanometers thick if you can imagine
08:05
such a thickness to billionth of a meter
08:09
and to billionths of a meter maybe only
08:12
10 or 20 depending on the size of the
08:15
atoms 10 or 20 atoms thick this chromium
08:18
oxide layer that’s on the top here and
08:20
is invisible is going to start melting
08:25
at about 3,000 degrees C and it’s going
08:29
to boy off at 4,000 degrees C now
08:34
although this stainless steel will
08:35
actually melt at around about probably
08:37
14 1500 degrees C it’s actually got to
08:42
get up to something in the region of
08:43
about maybe 3,000 degrees C before it
08:46
boils ie vaporizes and disappears
08:50
now if we’re going to engrave this
08:52
material at some stage in the future
08:54
which I believe we can and will then
08:56
we’ve got to actually start vaporizing
08:59
the material underneath but that’s a
09:03
long way off let’s deal with this
09:05
problem to start with now as I said
09:08
we’ve got a very thin layer here and it
09:11
looks as though we’re going to have to
09:13
add heat to it to get these colors but
09:16
we only want to add heat to this layer
09:20
we don’t want to go through that layer
09:22
and damage the material that’s
09:23
underneath so we’ve got our very
09:26
accurate control of temperature to try
09:28
and manipulate the thickness of this
09:30
very thin film that’s on here now we
09:33
started to investigate this problem last
09:35
time when we decided that we got a beam
09:38
which was this size and we could inject
09:44
a small pulse of energy into it and do
09:47
some damage the problem is if we use one
09:51
of these very short pulses here we can
09:56
put something like 10 or 11 kilowatts of
09:59
energy into the peak power of that pulse
Transcript for the Search for Fiber Laser Color Marking (Cont…)
10:01
and we have seen that yes we are able to
10:05
do quite significant damage here because
10:08
we’ve got this yellowing effect so that
10:10
indicates that we are producing quite a
10:12
bit of heat but with this test I was
10:15
only running at 250 millimetres a second
10:18
we were just doing single little pulses
10:21
now there are many strategies that we
10:23
can adopt to improve the heating of a
10:28
particular spot one of the first things
10:31
we can do is to increase the frequency
10:33
of these pulses so that we get the next
10:36
pulse just here and the next pulse just
10:40
here and the next pulse just here so
10:43
that first pulse has been heated several
10:45
times before the pulse has moved off
10:47
into new pastures so by overlapping the
10:51
pulses like this we can build up heat in
10:53
one particular area even though they’re
10:55
very very small amounts of energy and
10:59
heat provided we keep the heat in the
11:01
same spot we can
11:02
probably some damage now that’s one
11:05
strategy that we can adopt I’ve drawn up
11:08
a chart here for each one of my pulses 2
11:12
4 6 8 sound so to give me an idea of the
11:16
number of pulses per millimeter that
11:18
running at different speeds will produce
11:21
four different kilohertz for different
11:24
frequencies we will hit the job eight
11:27
thousand five hundred times per
11:28
millimeter with that pulse so that’s
11:33
what this chart shows and it’s a useful
11:36
chart because it does give us an idea
11:39
that if we’re burning too much with this
11:41
particular setting at a hundred
11:43
millimeters a second we can increase the
11:46
speed and as we increase the speed look
11:48
we can go from eight thousand five
11:50
hundred down to 850 of course we’ve also
11:53
got power as well that we can play with
11:55
so we could leave this at 8,500 pulses
11:59
per second and reduce the power because
Transcript for the Search for Fiber Laser Color Marking (Cont…)
12:01
we’ve got control of percent power as
12:03
well so there’s another variable that we
12:06
can use to play with the amount of power
12:08
that we’re going to dispense now the
12:10
other thing that we can also take a look
12:12
at is this ratio down here now it’s the
12:16
ratio of on to off and basically it’s on
12:21
one and off 588 whatever right so the
12:29
ratio of on to off is very very large
12:31
which means that even though we put a
12:34
little pulse of energy in there and
12:35
heating we’ve got a huge amount of time
12:38
for it to cool or to radiate the heat
12:41
away through adjacent atoms so that’s
12:45
not good and another reason why we need
12:50
to keep the frequency as high as
12:51
possible so that we can keep the heat in
12:55
the same spot almost and I’ll probably
12:57
be doing a test square like this all
13:00
right it’ll only be a small one maybe
13:02
five millimeters square so the first
13:05
thing that we can do is fill in this
13:07
square with pulses at 8500 per
13:11
millimeter and we can go across like
13:14
this with a line
13:16
we can fly back or we can come back with
13:19
another line we can fly back we can come
13:23
back with another line that’s one of the
13:25
options that we’ve got another option
13:27
that we’ve got is to come across and
13:30
then go back come across and go back so
13:35
we can either do single scan like this
13:39
or we can do double scan like this now
13:43
which one of those do you think would be
13:45
a better strategy for keeping the heat
13:48
into the inter into this area that we’re
13:51
working with well my belief is that
13:54
probably it’s this first one we’ve
13:57
heated this line up so here we’ve got t1
Transcript for the Search for Fiber Laser Color Marking (Cont…)
14:01
and by the time we get to the end here
14:03
we’ve got T Max right because t1 is now
14:07
cooled off so if we now jump back to the
14:11
beginning of this line again we will
14:13
have T Max against T 1 and this one will
14:16
be cooling down while this moves along
14:19
so we shall get a much more even flow of
14:21
heat across these lines whereas if we go
14:24
this way like this we’ve got T Max here
14:27
and then we’ll immediately turn round
14:29
and we’ll have 2 T Max’s here and then
14:31
we’ll be running back this way where
14:33
we’ve got t1 and we’ll have t1 again now
14:36
there are other things that I found out
14:37
that you can do in the software you can
14:40
make you can define a little circle for
14:42
example so although we’ve got a point 6
14:44
dot like that we can make that point 6
14:48
dot do things like this it can work its
14:52
way across the job in a spiral so
14:55
there’s another way that we can create
14:57
heat over lapping heat and then we’ve
15:00
got all these various pulses with their
15:02
spread of power so we’ve got an infinite
15:06
number of possibilities for trying to
15:11
solve this problem where do we start now
15:15
we’ve had a little bit of a fail of the
15:16
power based on aluminium test but of
15:20
course stainless steel is going to be
15:21
completely different maybe that would be
15:23
a good strategy to see just what happens
15:26
when we run this same pattern on
15:28
stainless steel perhaps I’ll give me a
15:31
little bit of a pointer as to where we
15:33
should start our tests where you might
15:36
even magically get some colors of midair
15:39
without even trying so I think it’s off
15:41
to the Machine in the cold workshop
15:43
after all okay now what I’ve got here is
15:45
a piece of 304 L first of all it’s low
15:50
in carbon and secondly it’s bright
15:52
annealed now it might look like a mirror
15:55
finish on there but in fact it’s been
15:58
prepared in a vacuum furnace with argon
Transcript for the Search for Fiber Laser Color Marking (Cont…)
16:02
and hydrogen I believe to exclude oxygen
16:07
particularly during the process and it
16:11
then has to be quenched and it comes out
16:13
with this nice clean mirror looking
16:15
finish even though it’s not been
16:17
polished so there’s no built-in oxide
16:22
within the surface what’s actually
16:25
happening here is as soon as it gets
16:27
exposed to the air you’ve got this thin
16:29
film of oxide that builds up on the
16:31
surface itself so there’s a controlled
16:34
amount of oxide there on this particular
16:36
type of product
17:06
[Applause]
17:22
things that we’re gonna have to deal
17:24
with the longer function
17:27
they’re the only ones in synchrony
17:32
the good news is without even trying
17:36
here in this daylight we’ve got quite a
17:40
few sort of colors so we’ve even gotten
17:43
a hint of a blue there so yeah we’ve got
17:49
a bit of a starting point here for some
17:50
of the colors now up this end here I’ve
17:55
got virtually no fail at all it’s just a
Transcript for the Search for Fiber Laser Color Marking (Cont…)
18:00
smooth surface whereas as I get down
18:02
here down at this end we’ve definitely
18:06
got damage to the surface I can feel
18:09
engraving so that again is another
18:13
useful and we’ve got engraving in this
18:16
middle area here as well so I think
18:18
we’re gonna have to start up at this
18:19
into the range here with small posters
18:22
so that we don’t do any damage to the
18:24
material we’re trying to thicken the
18:26
oxide film remember where as definitely
18:28
here we’re burning right through the
18:30
material so all these lovely pastel
18:32
colors but because these are not real
18:34
colors are said before yes it depends on
18:37
the frequency of the light that’s
18:38
hitting the job and we’ve got a very
18:40
restricted range of frequencies with
18:42
this white LED light I had half a dozen
18:44
attempts at trying to do something
18:46
earlier with the artificial light to be
18:49
honest I was wasting my time because the
18:53
way that light interacts with these
18:54
colors it’s got to be daylight to get
18:57
some sort of idea of whether I’m making
18:58
any progress so here I am another day
19:02
and another piece of material this is
19:04
stainless steel 304 L and as you can see
19:08
it’s been protected by a plastic film so
19:11
I’m taking the plastic film off never
19:14
been touched by human hand except to
19:17
hold that corner those colors that we
19:20
produced on there even though this was
19:22
red-hot it didn’t damage the surface and
19:26
I’ve still got a reflection in that blue
19:29
and all the colours around the outside
19:31
this is transparent this colour that’s
19:34
what I’m basically trying to achieve on
19:36
this surface here if I get through the
19:38
film then I think I’m probably not
19:41
succeed using my colour chart here that
19:43
I produce yesterday
19:45
which you can’t see in this light I’ve
19:47
chosen a speed to try and get me a blue
19:52
now technically blue was produced when
19:56
we got the hottest color if you remember
19:59
it glowed red hot and then when it
Transcript for the Search for Fiber Laser Color Marking (Cont…)
20:01
cooled down it cooled down to blue my
20:04
first attempt is still going to be at
20:06
the speed of 250 millimeters a second
20:08
I’m going to be running at a frequency
20:09
of 400 kilohertz 100% power and a pulse
20:14
width of 6 nanoseconds and just one pass
20:20
it’s definitely a navy blue hue it’s
20:24
almost black and in fact to be honest
20:27
whichever way I look at it in the light
20:29
as I turn it round it remains black so
20:33
hey at our first attempt we found a way
20:36
of producing a black mark on stainless
20:38
steel now black would imply that we’ve
20:43
got complete destructive interference
20:46
between the light waves we’re sending
20:49
white light in and we’re getting nothing
20:51
out now this seems a bit
20:53
counterintuitive but I’m going to see
20:56
what happens when I do nothing other
20:59
than increase the number of passes so
21:02
we’re going to run the program twice
21:06
[Applause]
21:09
well that’s a little unexpected going
21:13
twice as actually
21:16
created a lighter blue well on that
21:20
basis logic says if I do it three times
21:22
I should get an even lighter blue
21:25
[Applause]
21:31
there’s any significant difference in
21:33
the color there so it looks as though
21:36
two passes is a good starting point
21:38
established the surface to such an
21:40
extent that I haven’t got a reflection
21:43
let’s go back to two passes at this time
21:48
I’m going to reduce the power by 50%
21:54
[Applause]
21:56
well it’s a paler blue but it’s a pretty
21:58
washed out pale blue so we’re going back
Transcript for the Search for Fiber Laser Color Marking (Cont…)
22:01
to the success will blue – passes so now
22:05
what we’re going to do is try and change
22:07
the frequency and see what effect the
22:08
frequency has technically the frequency
22:11
is going to only increase the amount of
22:15
repetitions that we get so we’re going
22:18
to actually be putting in more power if
22:21
I increase the frequency so let’s go
22:24
from 400 up to 600 to start with well
22:33
that hasn’t worked is it so let’s go the
22:36
other way
22:36
and go down from 400 to 200 if anything
22:40
I would say is are sort of slightly
22:42
Goldie it’s almost a coffee color latte
22:46
actually that does remind me it’s bit
22:49
frosty outside this morning and a cup of
22:52
coffee would certainly help me warm up a
22:55
little bit so at this time let’s change
22:57
the pulse width to 4 nanoseconds
23:06
it’s nothing like these here is it so
23:08
it’s amazing how sensitive it is to
23:10
various factors so let’s go back to that
23:15
and let’s try and change the speed a
23:18
little bit so by increasing the speed
23:21
from 250 to 400 in fact I’ll tell you
23:24
what we do a double it will go up to 500
23:27
which means that my dots are now twice
23:31
as far apart so every millimeter is now
23:34
receiving half as much power and this is
23:37
a very good comparison because we found
23:39
that reducing the power to 50%
23:41
completely destroyed the color so it
23:44
does reducing the speed cause the same
23:48
issue I think the answer is no because
23:51
we’ve got the same power in each dot so
23:55
it’s a different way of taking the power
23:58
away something that’s a much brighter
Transcript for the Search for Fiber Laser Color Marking (Cont…)
24:02
light when we put half as much power in
24:05
by playing with the speed we get a gold
24:10
when we reduce the power by 50% we get a
24:15
pale-blue reducing the power one way is
24:18
not the same as reducing the power the
24:20
other way so I think we ought to start
24:21
making a note of the parameters for
24:24
getting all of these colors these are
24:27
all very very close to each other in
24:30
parameter settings and you’ve got this
24:33
whole range of fairly weak colors it has
24:36
to be said at the moment well I’ve had
24:38
to give in a little bit of heating might
24:41
allow me to carry on in here because my
24:44
hands are just about to drop off we’ve
24:46
go back to our base parameters which we
24:48
found and this time we’ll change the
24:51
speed from 250 down to 200
24:54
[Applause]
24:58
so reducing the speed there’s not had a
25:02
great deal of effect so we’re still
25:04
running at 200 millimeters a second and
25:07
we’re doing a single pass and well we’re
25:15
almost back to that that subtract one
25:17
pass at 150 well the bad news is I can’t
25:25
record any of these colors under my
25:27
microscope because it is a white LED
25:31
light and it completely destroys all the
25:34
colors that you can see here I’ve tried
25:37
to look at my best blue swatch under the
25:41
microscope
25:41
now this is under the microscope in
25:44
daylight when I turn on the white LED
25:47
light just in a few places mmm we’ve got
25:52
the little flashy hint of Blues now as I
25:56
said this is a an LED light which has
25:59
obviously got a limited color range and
Transcript for the Search for Fiber Laser Color Marking (Cont…)
26:03
it seems that yellow is something it’s
26:05
much happier with there’s something
26:08
interesting about that pattern I used a
26:11
point one spacing between my lines but
26:14
obviously burning through the very thin
26:17
oxide layer that’s on the surface so if
26:21
I’ve burned through the oxide layer
26:23
where’s the colour coming from
26:25
it’s amazing what observation and
26:28
accidents can do for you isn’t it you
26:29
know I think that what we’re seeing
26:31
there is a freshly cut groove that’s
26:35
been burnt into the material and then
26:38
the oxide has formed onto the surface of
26:41
the freshly cut material to a specific
26:44
thickness depending on the temperature
26:46
of the cut but it also explains why when
26:51
I touch this material I can fail some
26:54
roughness it’s a different texture for
26:56
the surface and also when I look at the
26:59
reflections in here I can’t see a
27:02
reflection in there so this is not the
27:05
same oxide surface that we had when we
27:09
heated it up very interesting
27:11
observation so I’ve taken a photograph
27:12
for the swatch so that I could annotate
27:15
it to tell me to tell me which settings
27:18
I was getting for each one of these
27:19
colors they they’re not really quite
27:23
what I’m seeing with my eye
27:25
perhaps I would just go in and use Auto
27:27
levels in Photoshop here to just enhance
27:32
the picture a bit they are slightly
27:35
exaggerated from the colors that I can
27:37
see but they are still roughly fortunate
27:40
they give me a good idea of what’s going
27:44
on I think we’ve made a pretty major
27:47
discovery here about how this light
27:50
system works in case I didn’t explain
27:53
myself very well I’m just gonna do a
27:56
quick sketch of what I see in the hope
28:00
that it may well clarify it for you let
Transcript for the Search for Fiber Laser Color Marking (Cont…)
28:03
me hand our burnt patch on here I
28:05
demonstrated to you that you could see
28:07
through the through the patch in other
28:10
words the coloring was transparent here
28:14
the colors are not really transparent so
28:20
that was a bit of a concern what was
28:23
going on why was I getting color but I
28:26
wasn’t affecting the film on the surface
28:28
I was somehow burning through the film
28:30
on the surface and yet I’m still getting
28:33
color so that part didn’t make sense and
28:37
then when I looked through my little
28:38
microscope and a certain circumstances I
28:41
could see when I looked at the lines
28:45
that were on my microscope like this I
28:48
could see little hints of speckles of
28:51
blue or yellow like this in the grooves
28:57
that wasn’t there continuously there
29:00
were just little speckles as I said to
29:02
the white LED light in my microscope is
29:05
distorting the colors it’s a very narrow
29:08
spectrum white light if I take a section
29:10
through the material what I was
29:13
effectively seeing was a little groove
29:17
like this where the beam had gone along
29:21
like this overlapping and caused the
29:28
groove and of course if you look
29:30
carefully you’ll see that there is hints
29:32
of this overlapping beam along the edge
29:36
of the group I have to
29:37
dude that this color that we’re seeing
29:40
in here is not sitting on the surface
29:45
it’s not a change in the thickness of
29:48
the surface as I was worried about
29:50
remember earlier I was saying we’ve
29:52
somehow got to change the thickness of
29:54
this film either up or down that was
29:59
rubbish
29:59
in hindsight but you may well also
Transcript for the Search for Fiber Laser Color Marking (Cont…)
30:02
remember something else that I mentioned
30:05
about one of the properties of stainless
30:07
steel you’ve only got to damage the
30:09
surface and within a few nanoseconds it
30:13
will automatically Hale over with this
30:15
film of chromium oxide so undoubtedly
30:19
that’s what’s happening in here when we
30:22
heat it up I’ll let thin sheet your
30:23
stainless steel this bit in the middle
30:26
got red-hot but when it cooled down it
30:30
cooled down to a blue so it would appear
30:35
that maybe the thickness of this film
30:38
this work is controlled in this groove
30:41
when the temperature cools down so if we
30:47
overheat it it will always be blue and
30:49
if we under heat it maybe it will be a
30:53
different color now with this new
30:55
possible mechanism of how the color
30:59
system works I need to go and have a
31:01
look that the various factors that we
31:06
have been playing with here what does
31:09
this mean in terms of power that’s gone
31:13
into the surface to produce these colors
31:15
so first of all I’m going to put all the
31:18
data onto that picture and to see
31:21
whether or not I can determine whether
31:22
there’s any special factors that will
31:25
allow me to manipulate the color well I
31:30
think it’s a little bit early to say
31:31
we’re having great success but from
31:35
nothing to finding blue and if you are
31:40
the colors um and much deeper
31:44
understanding of how the colors are
31:45
happening is certainly a major step
31:49
forward
31:50
so I think this is a convenient point to
31:51
stop for me to do a little bit more
31:55
documentation and analysis work and then
31:58
we can start off a new session with a
32:00
slightly different sense of direction so
32:03
thanks for your time and I’ll catch up
32:05
with you in the next session