03 – Light plus Aluminium and Water (23:18)

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 how fiber lasers work.

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.

How Fiber Lasers Work: Picture of Laser Marked Anodised Aluminium
How Fiber Lasers Work: Picture of Laser Marked Anodised Aluminium

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

In this session, Russ reviews the previous video and discusses his first laser marking attempts. He goes on to confirm that a fiber laser does not interact with glass.

Today’s technical session is all about the light, the properties of light and how that light can actually damage a surface. Russ then discusses how the relationship between light and the chemistry of a surface interact to give a mark.

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Transcript for Light plus Aluminium and Water

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00:01

well welcome to another session of the

00:04

fiber Lisa Learning Lab so that first

00:07

session was a long session because I

00:09

really wanted to try and cram in as much

00:12

information as possible about the

00:14

machine we managed to find out and

00:17

understand how a laser actually works

00:20

and then we’ve applied it to the the

00:24

constant output gas laser and then we

00:28

began to understand how a fiber laser

00:30

works and how the q-switch laser is

00:34

different from this one which is a mocha

00:37

laser so I feel fairly confident that

00:40

I’ve got a pretty good understanding of

00:43

how these two fiber laser systems work

00:46

now I can’t test this as a q-switched

00:49

laser because it isn’t I might be able

00:52

to simulate a q-switched laser with some

00:54

of the forces but I don’t know because I

00:57

haven’t used this machine before now the

01:00

most that I used this machine was last

01:02

time when I guess that some parameters

01:06

to run this very simple little test here

01:09

I used something like a 60 nano second

01:13

pulse and some other speed and frequency

01:18

parameters which I guessed at and well

01:22

we got a result what we proved last time

01:26

was that different materials react

01:28

differently to different frequencies of

01:31

light because we’ve managed to produce

01:35

that surface mark there on the constant

01:39

output glass tube laser which runs at

01:42

ten point six microns wavelength whereas

01:45

when we did the second mark there I

01:49

place the glass directly on top now

01:53

after we’d finished filming I thought

01:54

that was really a little bit cheating

01:57

because we did make a very small mark on

Transcript for how fiber lasers work (Cont…)

02:00

the underside of the glass but then I

02:04

realized that that mark on the underside

02:05

of the glass was really a reflection or

02:07

reaction of the material that we were

02:10

producing when we produced this white

02:12

mark

02:13

so subsequent to that what I did was

02:17

this I put some two mill spacers down

02:20

and I produced the third mark no

02:24

different than the second mark except

02:26

there was absolutely zero effect on the

02:31

glass and it just proves that that the

02:34

light beam was passing cleanly through

02:36

the glass ignoring the glass and all the

02:38

power was going into doing damage to the

02:41

surface of this black anodized material

02:45

so today’s technical session is all

02:48

going to be about the light and the

02:51

properties of light and how that light

02:53

can actually damage this surface and

02:56

then we’re going to talk about this

02:58

material and this surface and work out

03:01

how the relationship between the light

03:03

and the chemistry of this surface

03:04

creates this result now we’re here we’ve

03:08

got a data sheet supplied by jpt and

03:12

there’s several interesting pieces of

03:15

information on here which was useful for

03:17

us well I did mention to you I think in

03:19

the previous session the claim for this

03:21

particular machine is 0.06 spot where

03:25

there is 0.063

03:27

spot size and it says here that the

03:32

focal length is 254 millimetres 254 10

03:36

inches so that agrees with what I’ve

03:39

seen on this machine and it says that

03:41

it’s got a working depth of field and

03:43

here we can see look the depth of field

03:45

which is the useful part of the beam

03:48

where the focus is remaining good enough

03:52

to produce a spot size of 0.6 0.063

03:57

there’s another interesting piece of

03:59

information here which they’ve given us

Transcript for how fiber lasers work (Cont…)

04:00

which tends to possibly confuse this

04:04

true focal point and that’s this piece

04:10

of information here they’re telling me

04:12

this this beam which comes out of the

04:15

laser is a what they call an M Squared

04:19

of 1.3 now M Squared is a

04:25

definition which is used to define the

04:27

quality of a laser beam one is a perfect

04:31

Gaussian distribution an M 1.3 varies

04:36

very slightly away from a Gaussian

04:38

distribution now I’ve talked a lot about

04:40

light and Gaussian distribution within

04:42

the beam in my other glass tube laser

04:45

series but for those people that haven’t

04:48

been looking at that because they’re not

04:49

interested in you know cheap Chinese

04:52

tubes I will just quickly go through

04:54

what this means and just here I’ve got a

04:59

little torch which is a cloaks

05:01

equivalent to the laser beam it’s got a

05:03

single LED in the end of it now when I

05:06

shine this light on this surface you’ll

05:07

see that it’s got a very bright

05:09

high-intensity whiteness in the middle

05:11

and then the intensity of the beam

05:13

gradually gets weaker and weaker as it

05:16

gets to the outside well we can see that

05:20

now on this white light but we can’t sit

05:24

on the laser beam because the laser beam

05:26

is invisible and this is a typical

05:28

normal distribution curve with the glass

05:31

tube plates are running a ten point six

05:33

micron wavelength it’s very easy to see

05:36

the damage and the shape of the power

05:39

distribution within the beam I call it

05:41

power distribution that’s really wrong

05:44

it’s a light intensity distribution

05:47

within the beam and if we take a look

05:49

here the light intensity when it reacts

05:52

with the acrylic has actually evaporated

05:57

away a shape which is equivalent to this

Transcript for how fiber lasers work (Cont…)

06:02

normal distribution curve let’s assume

06:04

that a beam was six millimetres diameter

06:06

well here we’ve got one to three

06:10

millimetres on one side of Centre and

06:12

three millimetres on the other side of

06:14

Centre so within the central two

06:16

millimetres of the beam we’ve got 68

06:19

percent of the total light intensity and

06:22

then when we drop out to the next

06:24

millimetre we’ve got fourteen percent

06:26

fourteen percent and then right at the

06:28

outside we’ve got next to nothing two

06:30

percent two percent we may have a six

06:32

millimetre beam going into the lens

06:34

we’ve really only got four millimetres

06:38

which has got any power and in reality

06:40

we’ve only got about two millimeters

06:43

with any significant power but what

06:46

you’ve got to remember is the focal

06:48

point the spot comprises the whole of

06:53

this energy distribution so that means

06:56

when we’ve got a point oh six diameter

06:59

spot size for this beam it’s probably

07:05

only about 0.02 which has got the real

07:07

damage power in it so the next thing

07:12

that we have to understand is the nature

07:14

of light and how this very very special

07:19

light the laser beam which if you

07:21

remember we’re turning raindrops into a

07:23

tsunami wave so that everything is

07:26

acting together and we’re pushing them

07:27

down this pipe and concentrating them

07:30

and making them even more dangerous than

07:32

the tsunami wave so when you go outside

07:34

on a sunny day the first thing that you

07:37

feel is heat on your face for example

07:41

you think guides a bit warm out here

07:43

today where do you think that heat comes

07:45

from yeah I know it’s coming from the

07:48

Sun but how does it arrive at your face

07:51

it can’t be the same effect as when you

07:54

stand by a fire or a radiator the Sun is

07:58

90 odd million miles away and I know

Transcript for how fiber lasers work (Cont…)

08:01

it’s a very very bright bonfire the heat

08:05

does not travel through a vacuum you

08:08

probably know that intuitively because

08:11

how many of you have actually used or

08:13

daily use a vacuum flask or one of these

08:17

Yeti cups or something like that if

08:19

there are no molecules and there’s a

08:21

vacuum inside there heat will not travel

08:23

so this Sun that’s a long way away from

08:26

us and separated by a huge amount of

08:30

vacuum cannot send its heat directly to

08:33

us the only way that the heat gets to us

08:37

is in the form of light the light waves

08:41

are traveling from the Sun and can

08:44

travel in a vacuum and when they arrive

08:47

at your face

08:49

what they do they actually make the

08:53

molecules in your skin vibrate hang on

08:58

let’s go back to the first session

09:00

remember what I said

09:01

temperature vibration of molecules and

09:06

atoms the more they vibrate the hotter

09:09

they are so what’s actually happening is

09:12

sunlight one particular frequency of it

09:15

called infrared is actually hitting your

09:19

skin so there’s an energy transfer

09:22

between the light waves and the

09:26

molecules in your skin and you’re

09:27

stimulating the molecules in your skin

09:29

to vibrate faster and as they vibrate

09:32

faster they feel hotter because they are

09:36

getting hotter magnitude of vibration

09:39

equals temperature remember so the more

09:42

you can vibrate something the hotter it

09:44

gets now that’s a fundamental principle

09:46

that you must not forget because that is

09:49

how your laser beam is damaging the

09:51

surface of any material that it comes

09:54

into contact with it’s the same

09:56

principle as a rock falling out of the

09:59

sky that rock is completely harmless it

Transcript for how fiber lasers work (Cont…)

10:04

has energy it will do no damage until it

10:08

hits something and then there will be an

10:10

energy transfer from the rock to

10:14

whatever it hits ok that’s a physical

10:18

thing that you can imagine but it’s

10:21

exactly the same principle when we’re

10:23

talking about light the light travels

10:25

until it hits something and then you get

10:28

an energy transfer of the light energy

10:30

into the surface of whatever it hits and

10:34

although this might look like a solid

10:36

piece of material in reality the atoms

10:38

in this glass are probably there’s only

10:43

maybe I don’t know 1% solidity in there

10:46

it feels like solid to us but in terms

10:49

of light the light is the light at that

10:52

particular frequency is going right the

10:54

way through and there is not enough

10:56

energy in the photons to excite or do

10:59

any damage to this glass that

11:02

surface damage is caused when the when

11:05

the light energy hits the surface and

11:07

changes into stimulating heat which

11:11

raises the temperature of whatever this

11:13

black surface is hopefully you’ve now

11:16

got the idea there is no heat in the

11:18

light beam itself the light beam is

11:21

stimulating their material molecules to

11:24

vibrate faster and it’s the molecules

11:26

the vibration in the molecules that

11:29

determines their temperature so this

11:31

invisible light firing at the surface of

11:33

water is ten point six microns

11:35

wavelength but what it’s going to do

11:37

it’s going to stimulate the molecules

11:39

it’s going to excite them up to a level

11:41

where their temperature gets above a

11:45

hundred degrees C and we know what

11:47

happens at 100 degrees C steam it

11:51

evaporates so let me just press the

11:54

pulse button and show you what happens

11:55

when we fire the laser at water okay

Transcript for how fiber lasers work (Cont…)

12:01

let’s have a look whether I produced a

12:04

white spot under thee here none of the

12:10

energy has gone through the water the

12:12

energy coming from the light beam has

12:15

been converted into molecular vibration

12:20

and the molecular vibration has got

12:23

greater and greater and greater to a

12:24

point where the water can no longer

12:26

remain as a liquid

12:28

and it changes its state if we put a

12:32

piece of acrylic underneath here the

12:35

Acrylic is basically exactly the same as

12:37

water I know it doesn’t look like water

12:40

but trust me this is equivalent to ice

12:43

we’ve got a solid material here which is

12:47

solid at room temperature you heat this

12:49

up to 160 degrees C and it turns into a

12:53

liquid you heat it up to 200 degrees C

12:57

and it vaporizes just like steam so

13:02

that’s the way that this material reacts

13:05

to ten point six micron wavelength light

13:07

because it’s able to convert the energy

13:10

of the light

13:12

into molecular motion now keep stressing

13:15

this mechanism because it is a very very

13:18

important principle that you must always

13:20

carry with you when you see you’re doing

13:22

damage to material I’m going to leave

13:24

the guard open so that we can witness

13:26

this and I’m going to fire one micron

13:29

wavelength light into water through

13:32

glass and onto a piece of black anodized

13:35

aluminium it’s the same program that I

13:38

used to produce this stuff in the

13:40

background here

13:46

job done I didn’t see any steam

13:49

[Applause]

13:51

most of the light has gone through and

13:53

some of the energy has actually

13:56

stimulated the surface of the black

13:58

anodized aluminium when we passed the

14:00

light through glass

Transcript for how fiber lasers work (Cont…)

14:02

it had no effect at all so it’s just the

14:05

water that’s caused this attenuation of

14:08

this energy absorption of the light

14:10

energy and very little of the energy has

14:13

got through to stimulate the molecules

14:16

in the surface of that black anodized

14:19

aluminium that’s an interesting

14:22

experiment now I’m going to be using

14:25

black anodized aluminium with this one

14:29

micron laser because I think this is

14:31

about as close as I can get to a a very

14:35

good what I call a telltale material

14:38

that tells me what’s going on with this

14:41

light with the ten point six micron

14:43

laser acrylic was my favorite material

14:46

because you saw what it does it

14:49

evaporates the material like it

14:51

evaporates water the energy is converted

14:53

into evaporation now made with most

14:56

other materials that that can be damaged

14:59

by the ten point six micron wavelength

15:02

the molecules are heating up to a point

15:05

where they can no longer exist together

15:08

in the form that they are when water is

15:10

stimulated it heats up to its critical

15:15

temperature of 100 degrees C and then it

15:17

changes into another form it’s still

15:20

water but it changes into a gaseous form

15:23

called steam when you stimulate an

15:27

organic material like paper with ten

15:29

point six micron wavelength light it

15:32

it’s molecules vibrate faster and faster

15:35

and faster until it can no longer remain

15:40

as paper now just give you an example

15:43

here look I’m adding energy in the form

15:47

of a an external heat source I know you

15:50

could look at it and say yeah I just I

15:52

saw you add heat to it that’s why it

15:54

burnt for those of you that have not

15:56

seen

15:58

constant laser beam before coming across

Transcript for how fiber lasers work (Cont…)

16:02

here in space is that invisible beam and

16:06

it goes in there hits a mirror bounces

16:08

down and gets focused through there so

16:11

at this point we’ve got an unfocused

16:13

later bee and a piece of paper now I

16:19

didn’t start that fire with a flame I

16:23

started that fire with light so

16:27

something started off as paper it got

16:31

excited by light hitting its molecules

16:36

the molecules vibrated faster and faster

16:39

and faster until a point where they

16:41

could not exist together the independent

16:45

atoms that formed the molecule decided

16:48

to break away from the partnership form

16:50

a relationship with other chemicals

16:52

other elements that were around like

16:55

carbon and oxygen

16:58

and they produced this ash material this

17:01

is a chemical change that took place

17:04

because of stimulation it’s a different

17:08

process to the stew the process of state

17:12

change where it changes state from water

17:15

to steam so we’ve got these two distinct

17:17

processes that can take place when we

17:20

fire light at a material so here that

17:25

paper that’s no longer paper

17:27

it’s basically shaking itself to pieces

17:30

what are we looking at here to create

17:32

this sort of change is it evaporation

17:36

process is it a chemical change well to

17:43

investigate that we need to understand

17:45

what this material is this black

17:48

anodized aluminium here is a piece of

17:51

raw aluminium now what we’re looking at

17:54

there is looks like a piece of metal in

17:59

reality on that surface there there is a

Transcript for how fiber lasers work (Cont…)

18:04

very very very thin film of oxide now

18:08

oxygen is a very very volatile material

18:10

it’s a gas that we breathe but hey God

18:16

didn’t trust us with it he only gave us

18:18

20% because it was so dangerous and he

18:20

gave us 80% nitrogen but that oxygen

18:24

combines very easily with metals but as

18:28

soon as it combines with the metal the

18:30

reaction stops so we get a very very

18:33

very thin film of aluminium oxide on the

18:37

surface of this material that looks

18:39

exactly like raw aluminium the raw

18:43

aluminium has just underneath the

18:45

surface there we’re talking about one or

18:47

two atoms thick you will normally

18:49

recognize aluminium oxide it’s a white

18:53

substance that they use in grinding

18:56

wheels and in sandpaper okay so it’s not

19:02

white there but that’s only the glue

19:04

that’s holding it to the background to

19:05

the paper so the process of anodizing

19:09

this material starts off

19:11

by converting this surface here this

19:14

metallic surface into aluminium oxide

19:17

which is a nonmetal and as I’ve just

19:22

shown you with the grinding wheel this

19:25

aluminium oxide is a crystalline

19:28

material and it forms little crystals

19:29

all over the surface micro crystals now

19:32

this structure here on the surface

19:35

that’s been created by a an electrolytic

19:38

process is incredibly thin still it’s

19:43

still only somewhere in the region of

19:45

three maybe five microns maximum

19:48

thickness five millionths of a meter

19:51

that here is about five times thicker

19:53

than the aluminium oxide layer that’s on

19:56

the surface of an anodized aluminium but

19:59

of course in real terms that probably

Transcript for how fiber lasers work (Cont…)

20:01

means it’s around about I don’t know two

20:04

three four hundred atoms thick so it’s

20:08

actually in atomic terms a very thick

20:10

layer but even so there are still

20:13

crystal structure there which has got

20:16

voids between them but then we’ve got

20:19

we’ve got the outside world which might

20:21

be full of chemicals it could be liquid

20:24

water it could be acid it could be

20:26

anything that’s corrosive could leach

20:29

through those small voids and attack the

20:33

aluminium that’s underneath having put

20:36

the hard oxide layer on the surface they

20:39

then coat it and fill in the gaps with

20:44

some special chemical a sealant but

20:48

often before they put the sealant on it

20:50

can go through a secondary process and

20:53

this becomes then the third process the

20:56

second process being to dip this white

21:01

aluminium oxide some of the pores

21:04

between the crystal structure has been

21:06

filled with a black dye and in this

21:09

example here it’s been filled with a red

21:12

dye but this is still anodized aluminium

21:16

the process of anodizing is the process

21:20

of converting the material from raw

21:22

aluminium into an aluminium oxide

21:25

and then everything else on top of that

21:27

is to preserve the integrity on the

21:30

surface we’ve got the sealant and once

21:33

that gets heated up to say 200 degrees C

21:36

it will evaporate so that then exposes

21:39

the water-based black dye that’s in

21:43

between the crystal structure to become

21:46

excited although water and glass might

21:49

look transparent to us at these other

21:51

wavelengths of light glass and water

21:54

react differently I keep saying the

21:57

light has heated the material up no the

22:00

light has stimulated the material heat

Transcript for how fiber lasers work (Cont…)

22:02

itself up that’s the critical thing that

22:04

you must bear in mind the aluminium

22:06

oxide can be stimulated it has got to be

22:10

stimulated to about 2,000 degrees C

22:14

before turn to liquid and 3,000 degrees

22:18

C before it’ll vaporize off so if we can

22:21

see the gray aluminium through there we

22:24

know that we’ve achieved over 3,000

22:27

degrees C now I know these concepts

22:30

these numbers they sound incredible it’s

22:32

it’s almost like science fiction but

22:34

these are not things that I’m surmising

22:37

these are absolute facts that you can

22:40

chant check for yourself

22:42

so that’s why I should be using this as

22:45

a tell tale material when I come to look

22:48

at the various power capabilities of

22:52

various pulses and frequencies when

22:54

we’re testing this machine later on well

22:58

I think that’s enough of my silly

22:59

pictures and stupid science today thank

23:03

you for your time and patience and this

23:05

is going to lead on to another fairly

23:08

serious physics lesson when we look at

23:11

this subject next time Calem arcing of

23:15

stainless steel

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