06 – The Search for Colour Part 1 (32:08)

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

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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

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look through these results I will make a

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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

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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

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a yellow here even at four seconds for

02:19

nanoseconds so yeah we’ve got a

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relationship at the moment where we see

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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

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of the preferred numbers 600 here we are

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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

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maybe at five nanoseconds at six no no

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seconds as well now we come to 400

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kilohertz and there’s not supposed to be

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much happening there at fall killer 400

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kilohertz but look which still got here

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there is a very there is a very dark

03:13

pattern there and it is quite yellow

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here we’ve got a definite yellow pattern

03:18

and some of these here are yellow as

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well so it looks as though we’ve got

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quite a lot of power in this region here

03:27

even at 400 kilohertz and now we drop

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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

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above it at 4 nanoseconds and even the

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one below at 8 nanoseconds has got a

03:44

brown a yellow hue to it as well and

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even 13 in a second so we’ve got power

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in this region here and here we are at 2

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kilohertz where we’re supposed to

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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…)

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nanoseconds but not much else down this

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chart then this one was a little bit of

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a puzzle because we’re supposed to come

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across peak power here for 13 and 20

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nanoseconds but these don’t look

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particularly yellow now between 13 and

04:18

100 nanoseconds will looks as though

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we’re beginning to develop this broader

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d part of the pulse up to now 2 4 6 8

04:29

these have been very sharp peaky poses

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so let’s just see what happens 2:30

04:35

we’ve got no distinct yellowness there

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and here we are again look there’s lots

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of these max powers that fall into this

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category here and really when we look at

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these none of them are really very

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yellow they’ve lost that punch let’s

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call it that that probably still got

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quite a lot of power in them but they

04:55

don’t any longer burn the material and

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then the rest of them which are hundred

05:01

and fifty up to 350 150 up to 350 all of

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them occur on this page here and if we

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take a look it’s rather interesting that

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first of all they’re all lines which is

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rather strange we’ve lost our pattern

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but all these lines have got a slight

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yellow hint to them so we’ve got I think

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heat coming from a different direction

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we’ve got sustained heat this time as

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opposed to peak heat so I think when we

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look at these lower pulses we’ve got to

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consider that we’ve got a different way

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in which we’re heating up the material

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now that’s as low technically as I

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should have gone but of course I went

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lower than that and I’ve gone right the

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way down to 5 kilohertz where basically

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I’ve got rubbish results it’s a bit

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expected because I’ve dropped off the

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bottom of I’ve dropped off the bottom of

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their chart there and serves me right so

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there are interesting correlations in

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those results to these patterns and

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pulse Peaks

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which we will be able to use and refer

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to as we discovered last time one of the

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most important things is try to work out

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how we’re going to get heat down into a

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specific spot now look here’s what we’re

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trying to decode what’s going on here

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and if you remember in the last session

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I did mention to you that even though

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the hole of this center section here

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which finishes up as a blue went

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red-hot

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up at 800 900 degrees see it settled

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back down to this blue when it got to

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something like about 300 degrees C so

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regardless of how high the temperature

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went the oxide layer formed at a certain

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temperature where I suspect the oxide

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layer had reached a maximum thickness

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because regardless of how hot we made it

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we still got blue so the interpretation

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of that is because these are refraction

07:12

colors coming off of the under neath and

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you can see that even though it’s blue

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we can see the image of that little

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pointer on the surface underneath there

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so this blue color is completely

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transparent so our goal is to try and

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find a way of thickening this oxide

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layer that’s just here which is fully

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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

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which gives us this blue and everything

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else in between

07:56

now this clear layer that we’ve got here

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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

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such a thickness to billionth of a meter

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and to billionths of a meter maybe only

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10 or 20 depending on the size of the

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atoms 10 or 20 atoms thick this chromium

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oxide layer that’s on the top here and

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is invisible is going to start melting

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at about 3,000 degrees C and it’s going

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to boy off at 4,000 degrees C now

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although this stainless steel will

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actually melt at around about probably

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14 1500 degrees C it’s actually got to

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get up to something in the region of

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about maybe 3,000 degrees C before it

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boils ie vaporizes and disappears

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now if we’re going to engrave this

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material at some stage in the future

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which I believe we can and will then

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we’ve got to actually start vaporizing

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the material underneath but that’s a

09:03

long way off let’s deal with this

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problem to start with now as I said

09:08

we’ve got a very thin layer here and it

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looks as though we’re going to have to

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add heat to it to get these colors but

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we only want to add heat to this layer

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we don’t want to go through that layer

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and damage the material that’s

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underneath so we’ve got our very

09:26

accurate control of temperature to try

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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

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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

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of these very short pulses here we can

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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

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we’ve got this yellowing effect so that

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indicates that we are producing quite a

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bit of heat but with this test I was

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only running at 250 millimetres a second

10:18

we were just doing single little pulses

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now there are many strategies that we

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can adopt to improve the heating of a

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particular spot one of the first things

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we can do is to increase the frequency

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of these pulses so that we get the next

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pulse just here and the next pulse just

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here and the next pulse just here so

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that first pulse has been heated several

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times before the pulse has moved off

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into new pastures so by overlapping the

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pulses like this we can build up heat in

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one particular area even though they’re

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very very small amounts of energy and

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heat provided we keep the heat in the

11:01

same spot we can

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probably some damage now that’s one

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strategy that we can adopt I’ve drawn up

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a chart here for each one of my pulses 2

11:12

4 6 8 sound so to give me an idea of the

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number of pulses per millimeter that

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running at different speeds will produce

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four different kilohertz for different

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frequencies we will hit the job eight

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thousand five hundred times per

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millimeter with that pulse so that’s

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what this chart shows and it’s a useful

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chart because it does give us an idea

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that if we’re burning too much with this

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particular setting at a hundred

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millimeters a second we can increase the

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speed and as we increase the speed look

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we can go from eight thousand five

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hundred down to 850 of course we’ve also

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got power as well that we can play with

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so we could leave this at 8,500 pulses

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per second and reduce the power because

Transcript for the Search for Fiber Laser Color Marking (Cont…)

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we’ve got control of percent power as

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well so there’s another variable that we

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can use to play with the amount of power

12:08

that we’re going to dispense now the

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other thing that we can also take a look

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at is this ratio down here now it’s the

12:16

ratio of on to off and basically it’s on

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one and off 588 whatever right so the

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ratio of on to off is very very large

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which means that even though we put a

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little pulse of energy in there and

12:35

heating we’ve got a huge amount of time

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for it to cool or to radiate the heat

12:41

away through adjacent atoms so that’s

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not good and another reason why we need

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to keep the frequency as high as

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possible so that we can keep the heat in

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the same spot almost and I’ll probably

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be doing a test square like this all

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right it’ll only be a small one maybe

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five millimeters square so the first

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thing that we can do is fill in this

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square with pulses at 8500 per

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millimeter and we can go across like

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this with a line

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we can fly back or we can come back with

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another line we can fly back we can come

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back with another line that’s one of the

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options that we’ve got another option

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that we’ve got is to come across and

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then go back come across and go back so

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we can either do single scan like this

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or we can do double scan like this now

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which one of those do you think would be

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a better strategy for keeping the heat

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into the inter into this area that we’re

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working with well my belief is that

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probably it’s this first one we’ve

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heated this line up so here we’ve got t1

Transcript for the Search for Fiber Laser Color Marking (Cont…)

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and by the time we get to the end here

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we’ve got T Max right because t1 is now

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cooled off so if we now jump back to the

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beginning of this line again we will

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have T Max against T 1 and this one will

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be cooling down while this moves along

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so we shall get a much more even flow of

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heat across these lines whereas if we go

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this way like this we’ve got T Max here

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and then we’ll immediately turn round

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and we’ll have 2 T Max’s here and then

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we’ll be running back this way where

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we’ve got t1 and we’ll have t1 again now

14:36

there are other things that I found out

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that you can do in the software you can

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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

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way across the job in a spiral so

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there’s another way that we can create

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heat over lapping heat and then we’ve

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got all these various pulses with their

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spread of power so we’ve got an infinite

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number of possibilities for trying to

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solve this problem where do we start now

15:15

we’ve had a little bit of a fail of the

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power based on aluminium test but of

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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

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when we run this same pattern on

15:28

stainless steel perhaps I’ll give me a

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little bit of a pointer as to where we

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should start our tests where you might

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even magically get some colors of midair

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without even trying so I think it’s off

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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

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with this nice clean mirror looking

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finish even though it’s not been

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polished so there’s no built-in oxide

16:22

within the surface what’s actually

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happening here is as soon as it gets

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exposed to the air you’ve got this thin

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film of oxide that builds up on the

16:31

surface itself so there’s a controlled

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amount of oxide there on this particular

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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

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here in this daylight we’ve got quite a

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few sort of colors so we’ve even gotten

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a hint of a blue there so yeah we’ve got

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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

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got damage to the surface I can feel

18:09

engraving so that again is another

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useful and we’ve got engraving in this

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middle area here as well so I think

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we’re gonna have to start up at this

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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