09 – RF CO2 Laser Source – Where Is The Magic?

0:01well thank you very much for joining me in another session about my little tangerine tiger

0:07now after the last session where we decided how the power was controlled i’ve done

0:14nothing more on the machine but i’ve done quite a lot of thinking can i start this session off with

0:19something rather shocking i think i’m going to have to reserve the right to change the title of my little

0:25machine from tangerine tiger to tangerine tabby cat i don’t think it’s

0:32going to turn out quite the way that i or you were dreaming that’s

0:37pretty bold statement but let me just begin to explain how this machine

0:43actually damages material and i think you’ll begin to see some of my

0:49disappointment now here in front of us we see the results of our mode burn

0:54now this is the mode burn from my 70 watt constant current machine this is the mode burn

1:02from the rf 30 watt machine running in more or less constant

1:09current mode 100 the same thing but this time it’s done

1:16with a beam expander which is three times this was two times beam expander this is

1:22three times beam expander now we talked about this last time but we didn’t really go into much of a

1:27discussion about it other than to say this was rubbish and this was more the sort of thing that i was looking for

1:34now i’m going to have to explain myself a little bit about that and why i want this rather than this ideally i’d like this

1:43but hey several things about this rf laser are different first of all coming out

1:49the laser the beam is not parallel it expands quite a bit more maybe two or three times more

1:55than that coming out of a glass tube machine that was disappointment number one and that in fact means that we put a

2:02beam expander in there like that to make the beam parallel

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

2:07okay now that automatically cost us to be found out last time two lenses in here cost us roughly four

2:14percent and four percent power so we’ve already lost power because we’ve had to adjust the beam

2:20i’ve had quite a few people ask the question why didn’t i use a three or four times

2:25beam expander because i’ve got plenty of room on the mirrors to do so it’s a difficult

2:30question to answer to somebody that cannot see what i can see they’re believers in what

2:37i call conventional lens theory and here we have a lens facing the work which is down here

2:44coming onto this lens we have parallel

2:49beings of light now that beam there happens to pass right through the axis

2:55of the lens this lens is designed to focus the beams i.e is trying to collect all

3:02the power into one spot so the beams that are on the outside here

3:09come in here and they focus say here like this

3:18now these beams are slightly closer towards the axis take a slightly different path and

3:24depending on the type of lens whether it’s a plano convex or meniscus if it’s a plano convex then

3:30they won’t take the correct path and they will actually

3:36focus a little bit further forward

3:42like that okay and the closer we get to center

3:48the further forward the focus point will move so let’s just take the extreme

3:54situation of this beam here that passes right through the axis of the lens

3:59where does that focus it’s a single beam and there is no other

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

4:08central focus only one the answer is really

4:15not eight meters away or eight millimeters that’s infinity it will never cross over itself

4:21because it is itself we’ve only got to move marginally away from the center and they will converge but where will

4:28they converge well the answer is probably a long way

4:33if we look at these rays and say well that ray is going over there that row is going out there this ray is

4:41going out here and this ray is coming out here what we’re finding is

4:46what you consider to be the focal point is this look we’ve got the line here which does that

4:56[Music] and that is what you would probably

5:01consider the spot size or

5:09the focal point so there is a footprint at the focal point

5:15through which all the rays will pass now that’s the important thing all the rays will pass it doesn’t mean

5:22to say they all focus at that point as you can see some of these rays are focusing

5:29way beyond the focal point now if this source of light here was uniform there

5:35would only be a small proportion of that energy which is focusing below the focal

5:40point and you would probably hardly notice it but that’s not the case with a laser beam because

5:46our laser beam has got an energy distribution [Music]

5:51which looks like that in other words we have got something like about 70 percent

6:02of the energy in roughly one-third of the width of the beam that means that

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

6:09we’ve got an extraordinary amount of energy concentrated around about the central axis of the

6:15lens now i’ve demonstrated this in several of my videos but there is a lot

6:22of power below the focal point that we can work with the reason why i’m telling you this is because the discussion about

6:30maybe using a beam expander to get a better focus i agree

6:37probably you would get a better focus so we’re going to take this gaussian distribution when it is coming out of the laser

6:45but by the time we’ve expanded it out to some other dimension what’s happened is

6:51our distribution is no longer like this it’s more

6:57like this in other words what we’ve done we’ve taken away the potential for this

7:04high energy which passes through the center and we’ve pulled it out away

7:10from the axis so that we can tame it and focus it and so we should be able to

7:17focus that beam a lot better if it’s bigger is that what i want

7:25i personally do not want that i want my beam to be untamed and i want this

7:32central core of energy because that is what i believe is going to do the damage to the material i’m not interested in this

7:39thing called a spot size or the focal point i want something else okay so that is why i have opted

7:46for exactly the opposite of this i’m trying to keep my beam as sharp

7:54as possible there we go we can prove that point there look

7:59opening the beam up makes it a lot blunter and if it’s blunter like this

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

8:07then we’re going to be able to focus it better that is how standard lens theory works and i agree with that completely

8:13it will focus it better but that isn’t what i want let’s go back to the pictures that we

8:19had last time where we saw we had control of the laser power

8:27with a square pwm signal what we have here

8:34is 30 watts every pulse is 30 watts we have no

8:41other wattage in this unit it always delivers 30 watts so how do you control

8:48the power here is one cycle now in that one cycle we have got fifty percent

8:56high and fifty percent low now when i say high and low

9:03i mean that is thirty watts of power and this is zero watts of power the

9:09actual rf laser is switching on and off and on and off all the time at varying frequencies

9:17which we talked about we can modulate the frequency but don’t worry about frequency because that’s not the issue

9:23the issue here is that we control power by [Music]

9:30changing this ratio here here we are percent power

9:37fifty percent power means we’ve got fifty percent on and fifty percent off ten percent power

9:43means we’ve got ten percent on and ninety percent off per cycle

9:48okay so 50 on and 50 off means that on average

10:00that bit there fills in this bit here what we’ve got is a total of instead of

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

10:0650 power we’ve got 50 of 30 watts so actually when we operate in this mode

10:14we’ve actually got 15 sorry we’ve got 15 watts [Music]

10:21because it’s only on for half of the time okay now let’s just take a look at how compare this to our

10:27constant power laser beam here we’ve got a surface

10:33here i’ve got my consonant power laser beam moving along at a constant speed so if i switch the laser beam on it will

10:40dig itself a hole because it’s constant power the hole will be

10:46like that and then it will switch off so it’ll make a hole like that now if i made that hole

10:55at say 200 millimeters a second

11:02and then i change the power on the laser beam to 100 millimeters a second

11:10what do you think would happen so i would probably expect to make a groove twice as deep

11:19because i’ve got the machine running so slowly that it’s able to do more damage before

11:24it moves on so this is a hundred millimeters a second

11:30of damage and this is 200 millimeters a second of damage so the depth of cut

11:36is proportional to the speed i’m going to put for cw which is constant wave which is when

11:44this machine operates at 100 percent

11:49or when we use a constant power laser this cw

11:59and our standard laser that we’re used to our glass tube which is on permanently

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

12:04and not pulsing would produce these shapes if we ran across

12:11at these speeds let’s assume that we said in both instances this is 100 30 watts

12:19and this is also produced by 30 watts with our glass tube

12:31they would both produce exactly the same result now i gave you some false information

12:38when i spoke last time i said to you imagine a candle flame

12:43and holding your hand over a candle flame now candle flame has got to come a constant output power and

12:50i talked about sharing power by moving your hand across slowly you share the power out a lot less and

12:58it settles in one spot more and you will burn your hand but if you move faster you can share

13:04that power out to such an extent that it doesn’t damage your hand i said but that wasn’t the case with

13:11this pulsing system because when you share it out you get a nice gentle beam like that

13:17and when you when you have a pulsing system every pulse would be the same power

13:26that was a bit of a misleading statement because now that i sit down and look at

13:31how this thing works it doesn’t work like that at all

13:37so for convenience again we’ve got fifty percent on

13:44and fifty percent off let’s just see what happens we know that this will always be

13:5230 watts of power it cannot change because the signal is controlled by

14:00this 5 volt value here and we’re not changing the value of this five volts at the

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

14:05moment okay this is the way in which it operates we change the power

14:10by changing the duty cycle of this square wave if we’ve got 30 watts here

14:17and it reaches this point here switches on and produces some damage in the surface

14:23switches off switches back on again switches off

14:30so we’re going to damage the surface like that if we have our constant laser

14:38running at 30 watts

14:44produce a groove like that not perforations but a continuous groove if this

14:51was running at 200 millimeters a second and this was running at 200 millimeters

14:56a second this little bit here and this little bit here

15:02is there any difference i’ve got 30 watts cutting that deep and here i’ve got 30

15:09watts from my glass tube cutting that deep

15:14there can’t be any difference because they’re both 30 watts so they both do the same amount of damage

15:22now come back to my burning hand principle the faster i run

15:30the more i will spread the power out and so consequently if i change this

15:36from 200 to 400

15:41[Music] my depth of cut is only going to be that

15:49deep [Music] because i’m running twice as fast therefore i’m spreading

15:55the same amount of 30 watts over the surface and i’m doing half as much

16:01damage because i’m running twice as fast does anything miraculously change with

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

16:06this system if i run this at 400 millimeters a

16:20second so i was totally wrong when i said that to you

16:26i’m not going to get little power pulses across my hand i’m going to get the same perforation

16:32pulses across there like that

16:38at the same energy density as i would if it was continuous you have to imagine

16:45that in this instance the candle flame is going on off on off on off at a rapid speed

16:52so all i would get is a perforated line instead of a continuous line with the same amount of damage

16:59or the same amount of hurt on my hand i’m puzzled at the moment as to whether this is going to do

17:04more damage it looks on the surface there as though i’m going to do half as much

17:10damage with this laser as i could do with 30 watts continuous i’m trying to

17:17work out what the advantage is of having a pulsing laser and of course

17:22this is assuming at the moment that the pit that we make is a dead copy of the

17:29on off it could well be that this pit is

17:37something like that because the power doesn’t get a chance to build up quickly it’s not a straightforward cut for

17:45instance if we had this at 10 like this

17:52[Music] what sort of shape pit would i make at 200

17:57would it be that depth or would it not get a chance to build up even and maybe i only got a little

18:03shallow cut these are all facts that we’re going to have to try and find out

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

18:10so undoubtedly this system can react a lot quicker than a glass tube system but it depends

18:16how you use the glass tube system you can’t emulate this process

18:22with a glass tube we’re gonna have to do some tests to find out about this

18:30how good is the relationship between this square wave here and the damage that we do i’m going to

18:37have to use this to start with because it’s the best way that i can see what’s going on

18:43inside there i can modulate this frequency along here if i change that to something like about

18:51500 hertz which i can do i’m allowed to do that because it says i

18:56can run it anything between 0 and 225 000. i decide to set the speed

19:03of my cutting to a thousand millimeters

19:10per second how long does it take to travel a millimeter so there’s one

19:17millimeter and there are a thousand of them in a

19:24second so that means that one millimeter actually

19:29equals one thousandth of a second which is one millisecond so every millisecond i

19:38travel a millimeter how long does it take for a single cycle if there’s 500 of those in a second

19:45it’s one divided by 500 point zero zero two seconds

19:52one second divided by 500 increments two seconds point zero zero two which

19:58equals two milliseconds

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

20:04so we’re going to travel one

20:09plus cycle and one minus cycle i should be able to run at a thousand

20:15millimeters a second and 500 hertz and

20:20produce a shape on the surface which looks like that where that’s one

20:26millimeter that’s one millimeter and that’s one

20:31millimeter that should be very very very very visible and that will tell me exactly what’s going on so in the

20:39previous diagram we showed that you could reduce the depth of cut

20:45on the rf and the constant power laser by

20:52changing the speed spreading the power out over more time over more distance

21:00whatever it is you could spread the power out and reduce the effect of 30 watts whether it be

21:07from an rf or a glass tube so even though i’ve still got the low speed

21:12200 millimeters a second if i reduce the power from 30 watts to 15 watts with a glass tube

21:19i can make the cut half as deep so i have two ways of adjusting the cut depth on a glass

21:26tube laser do i have the same options on the rf laser

21:32well the answer is no look i’ve got 30 watts here

21:38and i’ve always got 30 watts even if

21:43i make this into 10 and 90 all i should finish up with doing

21:50is producing a hole like that it will be the same depth because i’ve

21:56got the same amount of power 30 watts so i cannot change the depth of the cut

22:02with power you say well yeah look you have just reduced the power i’ve reduced the average power i haven’t

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

22:10reduced the specific power in a pulse the average over time

22:16has reduced but not the power per pulse so the only way that i’ve got to

22:24adjust the depth of cut with an rf laser is speed

22:33if i increase the speed i should decrease the depth of cut now that’s a very important fact

22:41and a big difference between the two systems now i’ve got no idea why the big boys

22:49decided to choose an rf laser other than the fact that it’s not chinese they may or may not have

22:57realized the mechanics of engraving

23:02when i watch their videos i have to say they do not understand the process that

23:07they’re selling now it sounds a bit arrogant and i’m going to explain why and you can go and look at some

23:13videos and demonstration videos and you’ll see exactly what i mean you need to understand

23:19the basic principles behind engraving it’s not even engraving it’s

23:25material damage so here we’ve got a surface

23:30and i’m going to fire a laser beam at the surface now bear in mind it’s a laser beam which is

23:35focused down to a point and that means that i’m going to put an incredible amount of power

23:41into the surface of this material now we won’t talk about the material for a minute we’ll just call it

23:47a material the first thing that’s going to happen is we’re going to produce

23:53a little bit of damage there and that little bit of damage is going to convert solid material

24:01into gas or vapor if i gave you a cup of water and you boiled it and didn’t have any

24:08windows open in the room that you boiled in that cup of water would

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

24:13fill the room with steam you know intuitively that vapor takes up a lot more room than

24:19solid obvious fact but one that everybody seems to ignore when they’re working with these machines

24:27if you convert a small amount of material into a vapor it will do

24:33exactly what this is shaped like and it will produce vapor

24:42which explodes upwards like this if you try and tunnel down deeper you’re

24:47converting material much more material into vapor but

24:53hang on this vapor here is in the way of the vapor that wants to expand up

24:58there as well and so it doesn’t what it does it expands out sideways like this because it can’t

25:06go upwards because there’s so much vapor going up that’s in the way

25:11and so consequently you get a lot of sideways spread the more you try the more

25:17material you try and convert the more you’re going to get this sideways spread a sideways explosion

25:22of expanding gas because it can’t physically move up quick enough and that is the stuff

25:30which if you happen to have stuff that’s blowing down onto the surface which

25:37i hasten to add when you look at the the big boy machines they always have air assist on their

25:44engraving they say it blows away the fumes no it doesn’t it blows the fumes back down

25:49onto the work where they condense and produce the horrible brown surface that you see on their work

25:57they do not understand this very simple mechanical principle it’s not even chemistry the basic principle engraving

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

26:04is very simple and i’ve i learned this a long time ago if i’m trying to engrave a letter like

26:10that which is solid click click click click click click like this that’s the last thing i want to do

26:17i am going to scan across there but what i really want to do i don’t have the option on a glass tube

26:23machine of being able to go blip blip blip blip blip blip

26:28like that now the way that i achieve that on a glass tube machine is

26:35to take that letter there but i will convert it into a bitmap i will make the black into grayscale

26:45and i will make the grayscale into mid gray

26:54why well because mid grey when it’s converted into a dithered

27:00image and i know this sounds a long way around but when you convert it into a dithered

27:06image i get this 50

27:11black and 50 white i get dots like this hang on

27:23isn’t that what we’ve got here the ability to produce dots

27:28of course it is the rf laser does something in a simple way that i i have to approach in a very

27:34complicated way on the glass tube machine now why am i doing this

27:40you might say well hang on you’re going to produce a gray letter no i’m not i’m going to produce a black letter

27:45because the dots are always one color it’s just that it’s not going to be a continuous line it’s going to be a

27:51series of dots like this which to the naked eye will look like a solid line the advantage is

28:00that all i’m going to do with these dots is to produce little teeny weeny

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

28:07explosions like this and my fumes will go upwards now if i’ve got my air

28:14management through the machine sorted out properly those upward fumes will not be blown

28:19down because i’m not going to use air assist on engraving they’re carried away

28:24by the high velocity airflow that i have over my work they do not get a chance to settle down

28:30this is particularly useful when it comes to engraving some really dodgy materials like leather leather

28:37produces huge amounts of fumes the oils and the the organic products in the surface it

28:44just absolutely cakes the place with brown if you do continuous scan lines the only way you

28:51can engrave leather in any way shape or form is to convert it to a bitmap and dither it but you dither it to fifty percent white

28:59and fifty percent black meet gray then you can produce a nice clean image on leather or wood

29:06or any other material you choose to use which produces nasty fumes and acrylic is one of them

29:12the fact that this rf tube can produce small controllable dots

29:18at high frequency has got great potential as far as i’m concerned

29:24for engraving it might be crap as a cutting machine but it has potential as an engraving

29:31machine if it’s understood how it works and you utilize it properly now i’ve not seen any evidence

29:38of proper utilization when i look at some of the demonstration videos on youtube they talk about resins

29:46and saps being pushed up and flowing and how you clean them up

29:52afterwards with a with just a damp sponge no you don’t clean up with a damp sponge

29:58you don’t even let them settle we have found a big positive

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

30:04maybe for an rf laser the first one now here’s our standard pwm 25 kilohertz

30:12and we’ve got it set at the moment to 50 percent power 50 on 50 off so we’ve actually got

30:1915 watts going into our job but as i said we haven’t got 15 watts

30:25we’ve actually got 30 watts going into every pulse but the pulse length is 20 micro seconds

30:32long that’s not very long 20 microseconds so a question we ask is how much damage

30:39can we do with 20 microseconds of 30 watts of power

30:44now that’s a difficult question to answer if it’s a piece of wood maybe it can do that much damage

30:53if it’s a piece of leather it may be able to do similar sort of

30:59damage if it’s a piece of acrylic the chances are

31:04it may be able to do that much damage if it’s a piece of glass it may be able to do that much damage

31:10mdf is very similar to acrylic

31:17i know this because of all my experimentation the materials themselves do not respond

31:23in exactly the same way for instance acrylic has got a melting point of 160 degrees

31:29c that’s pretty low and it boils at 200 degrees c so you said well

31:36they’re very very low temperatures i mean wood for example you have to be

31:41maybe 200 degrees c to to make it scorch and probably about

31:48350 degrees c to effectively start burning it and then you have to be about 4500 degrees c

31:57to burn away the carbon 4500 degrees c wood is easier to damage than acrylic

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

32:04which has got a threshold of disappearance of only 200 degrees c it’s all to do with the

32:10atomic structure of the material and how this 10.6 micron wavelength is

32:17able to excite the molecules in the material these molecules here are easily

32:22excitable whereas these molecules here are much more difficult to excite so it requires more power to cut acrylic

32:29and mdf than it does to cut wood or never 20 microseconds on wood

32:34might work and produce that amount of damage how do we get the same amount of damage

32:42onto acrylic but the answer is we’ve got to allow more damage time that might have to

32:49extend out to say something like about 60 microseconds

32:55now if it requires 60 microseconds of energy 30 watts to do that amount of damage

33:02that means the only way that we can get 60 microseconds

33:07is to change the frequency we’ve got to reduce the frequency from

33:12say 25 kilohertz to and bear in mind we’re now going to go from 20 which is the damage

33:18cycle to 60 so we’ve got to go three times as long or roughly one third

33:25of that frequency so we’ve got to come down to about eight kilohertz and at eight kilohertz we shall have

33:32sixty microseconds on and sixty microseconds

33:38off if we had to be using 50 percent power we could achieve 60 microseconds

33:45by choosing a different frequency and a different relationship in other words not 50 we could use a

33:52slightly higher frequency 12 maybe and use maybe 60 on

33:57and 40 percent off we’ve got all sorts of combinations that we can use but that’s

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

34:03why we’ve got control of the frequency and the mark space ratio or the duty

34:09cycle that’s why you need to understand the difference between duty cycle and modulation because at the end of the

34:15day it’s the pulse length the amount of time that you allow the beam on that’s going

34:22to cause the correct amount of damage for the material that you’re using it’s got nothing to do with this

34:29average power it’s all to do with the pulse power in one single pulse

34:39and because it’s so important i’ll try and sum it up very quickly in a few words average power

34:46has got nothing to do with pulse power

34:52you control this machine with pulse length and pulse length comes

34:58from a mixture of duty cycle and modulation the frequency so that’s

35:05enough theorizing well a lot of it’s not theory it’s fact the only thing that we don’t know is the

35:11relationship between this fact of the electronics and what happens in

35:17the real world what is the physics response to that electronic signal how quickly can the light generate

35:25enough photons to damage the material in relation to this signal i think the answer is

35:31we probably won’t notice the difference the only thing that we shall notice is actually this problem here the

35:38difference between the materials and we’re not using the best material in the world acrylic to start with

35:43but it’s the only material that we’ve got that enables us to look through the edge and see what’s

35:50happening so let’s go to the machine and see whether we can make this happen okay now look i’ve

35:55drawn a line here which is 20 millimeters long and here are the parameters i’m going to

36:00set for it we’re going to set it a thousand millimetres a second [Music]

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

36:0650 percent power now remember 50 power isn’t 50 percent power is fifty percent

36:12average power where i’ve got fifty percent high thirty watts and fifty percent low zero watts

36:21okay so i’ve still got thirty watts here for fifty percent of the time that’s the important thing to remember

36:28when you see these numbers i can go in here to advanced settings now so i’m going to set the modulation

36:33now by ticking this and i’m going to choose instead of 500 hertz which gives me one millimeter

36:41pulses i’ve chosen 250 so that it gives me two millimeter pulses

36:48this line is not very long and i’ve asked for a thousand millimeters a

36:53second now i haven’t messed around with the accelerations on this machine at the

36:59moment so it’s going to accelerate quite slowly and it’s not like scanning this it won’t

37:05accelerate and then produce a line and then decelerate this is not scan this is cut so what we shall see on this

37:13here is likely to be a start off from zero which means we should have quite a deep

37:20cut because the speed is zero remember even though we’ve got long pulses we shall also have

37:28slow speed which means we should get a deep cut to start with and as this speeds up and

37:34gets towards the middle of the line and hopefully by the middle line it will have reached a thousand millimeters a second and then

37:41it will slow down again so we should see deep cuts maybe

37:46some nice two millimeter pulses in the middle and then we should see some deep cuts again at the end

37:56and there we go it was as interesting as that so this image is basically the line tipped up at 45

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

38:03degrees so that i can see what’s happening you’ve got a reflection internally

38:08within the perspex of the image so the one at the top is the reflection the one that we’re

38:15looking at is the bottom image and there you see we’ve got our acceleration from zero

38:21where we’ve got a lot of cut depth gradually the cut depth gets shorter as we accelerate and then we move up to

38:29some sort of speed which is not a thousand millimeters a second and look we’ve got some pulses but those

38:36pulses are only three quarters of a millimeter apart so they’re not running at the correct

38:41speed and then we slow down again and you can see the depth getting deeper

38:47and we get to the end of the cut so that was pretty unsuccessful really wasn’t it apart from proving the point that the

38:54cut depth is dependent upon velocity now to ensure i get a thousand millimeters a second

39:00i’ve done two things first of all i’ve been into my vendor settings and set raised the limit from 500 to 1000

39:06millimeters a second so that when i get to this layer here i can actually use a thousand millimeters

39:12a second now i thought i was doing that when i did the single line but i think i might have made a mistake

39:19always admit to my mistakes because hey that stops you making the same ones maybe

39:25so there’s nothing wrong with this now scan because i’m going to use scanning and i’m going to put lines that

39:32are one millimeter apart so i’ve got about four or five lines in there one millimeter apart

39:38that should give us an idea of whether or not we’ve got good separation and good response time um

39:47if they did the line test look what i put in there 250 that’s not 250 hertz look what it

39:56says here 250 kilohertz there we go so my two grow cells let me down again

40:03they didn’t quite spot the fact that it said kilohertz so if we want 250

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

40:08in fact we’ll go to 500 which is what we originally thought we’d do which will be 0.5 kilohertz

40:17500 okay just check that it’s accepted 0.5

40:25yeah it’s happy to accept 0.5 so we should have one millimeter space one millimeter line if we’ve got all our

40:32calculations right and if the material responds

40:37at a fast enough rate it’s not going to be very exciting but hey let’s go for it

40:48look what we’ve got i think we have to be pretty impressed

40:53with that haven’t we because not have we got a thousand millimeters a second out of the machine so it tests the

41:00machine accuracy because we’ve got exactly one millimeter gap and one millimeter spacing

41:06across there it also tells us that we’ve got an incredibly fast

41:11response time switching the pulses on and off

41:17and the our acrylic is not as dead as i thought it was going to be if we try and go deeper we might not

41:24have completely square corners but i’m pretty impressed so far the only way that i can make that pulse

41:30deeper is to compromise on the speed

41:36so if i run at half the speed i should get twice the depth but still get one millimeter spacing we’ll now run

41:43this at 500 millimeters a second

41:50it’s under the microscope to see what’s happening but i can assure you that it’s very very interesting now

41:57these are the pulses at a thousand millimeters a second

42:02and you can see that i’m looking through the edge of the material and tipping it up okay so

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

42:09we’ve got you can see the depth of the pulse there and it’s looking

42:16pretty good so there’s the depth but when i tip it up you get a

42:22reflection but even so they’re looking pretty crisp

42:28now when we halved the speed here’s what we got

42:35they’re quite sharp edged pits they’re not quite as rounded as i expected them to be they’re

42:41sharper than i expected them to be but they do look shorter now why would

42:47that be what did i not think about so if i halve the speed from a thousand

42:54to five hundred millimeters a second my one millimeter per millisecond

43:00is going to change down here to 0.5 millimeters per millisecond

43:11so therefore i’m only going to see a one millimeter

43:25because i’m going to have half up half a millimeter up and half a millimeter down so if i keep the frequency the same

43:31i’ve got a half the distance which is what this is telling me but in addition

43:37to halving the distance what it’s also done has doubled the depth

43:42because we’ve kept the pulp because we’ve kept the pulse on longer so if i want to go back to two

43:49millimeter spacing i’ve actually got to change the frequency to

43:55250 hertz not 500 hertz i hope this little demonstration of my

44:00mistake shows you how heavily related that speed frequency

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

44:09mark space ratio are intertwined together i ran exactly the same tests on a piece

44:15of poplar plywood all the same settings

44:21then on a piece of mdf and then on a piece of glass all very interesting and actually quite

44:27a lot better than i thought they were ever going to be having started off asking the question

44:34am i going to be disappointed i think we’re coming up with a slightly better answer there is no magic

44:41there’s a lot of complexity but i’m quite actually excited again for the future so on that

44:47happy note i thank you for your time because my head hurts i don’t know about yours

44:53and I’ll catch up with you next session bye for now