20 – 20W MOPA Fiber Laser: Photo Engraving on Slate (58:26)

The Fiber Laser Learning Lab Series with Russ Sadler

In this Series, Lotus Laser have lent Russ a 20W MOPA 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.

They have been designed for high speed marking and the technology has been well tried and proven. There are limited “tricks” that the pulsing laser technology can perform. You enter predefined parameters for each marking “trick” you wish the machine to deliver , then stand back in amazement. Most correspondents tell Russ that they have bought their machine direct from China and received a machine and EZCAD software, preloaded with a few default parameters. No other instructions beyond the EZCAD manual are forthcoming.

Russ states “I am neither a teacher or expert in this field so you join me in my learning adventure with the warning that I have a simple but inquisitive mind and will probably make mistakes on my way to discovering the truth. I WILL oversimplify and maybe distort the scientific detail in my quest to build a simple picture of why and how this technology works. I am not trying to reverse engineer anything, just to break through the seemingly impenetrable ‘techno cotton wool’ that surrounds this amazing piece of science.”


In this session, Russ is investigating the performance of the fibre laser to engrave slate, compared to that of a standard CO2 laser machine. Even though the spot size is smaller and the speed is higher on the fiber laser, the results were disappointing. Until that is, Russ finds the secret sauce!

Previous VideoNext VideoSeries Menu

Video Resource Files

There are no more resource files associated with this video.

20W MOPA Fiber Laser: Photo Engraving on Slate
20W MOPA Fiber Laser: Photo Engraving on Slate

External Resource Links

Lotus Laser

MOPA 20 watt fiber laser

EZCAD Software

There are no more external resource links associated with this video.

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate

Click the “Show More” button to reveal the transcript, and use your browsers Find function to search for specific sections of interest.

0:01 welcome to another fiber laser learning lab no i’m not in the wrong place

0:07 and you’re right this is not a fiber laser machine but today um we’re going to do a little

0:15 bit of an investigation because i had a problem just recently as i mentioned in my other series my

0:21 stepdaughter is busy building a small business um with this with this

0:26 particular machine and uh she’s been engraving some slate

0:32 and i thought hang on the fiber laser does slate very very quickly this machine does it

0:39 moderately quickly now that i’ve pimped it up but surely we must be able to do a much

0:45much quicker job on the fiber laser machine i’m lost for words really because

0:51the fiber laser machine has got a spot size of about 0.06 or better

0:58this has got a spot size of about 0.1 so technically

1:04i should be able to run this slate on that machine over there much faster

1:10and with better quality i’ve been doing a little bit of fiddling behind the scenes fish very quickly

1:19and i can’t succeed now question is why can’t i succeed and that’s what we’re going to have a

1:25look at today first of all we’re going to have a quick run on here and see what the quality is and what the dot is that

1:31i can produce on this machine for dithered engraving and then we’re going to take a look at why

1:36i can’t achieve the same results on the fiber laser because i know that i can engrave slate on the

1:42fiber laser it does a fantastic job of engraving text but text is not the same as precision

1:49dots and that’s what i’m trying to establish just what it is i mean i’ve tried all

1:55sorts of parameters on the fiber laser machine so the only way to check it is to find out what dot i’m able to

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

2:02produce so first of all let’s just have a look at the results i get from this machine

2:12there’s 254 dots per inch or 254 pixels per inch on the image


2:34no [Music]

2:40i think you’ll agree that’s a pretty good image now i don’t need to run that image on

2:46both machines what i really need to do is to check the quality of the dots that i’m producing

2:53on this machine with this lens at this focus so we’ll just change the program and we’ll

3:00just run my little dot test [Music]

3:07okay it’s as simple as that so just so you can see where it is look there is

3:12the little dash and dot pattern here’s what it looks like at 50 times

3:19magnification there’s a scale on this side here which is in point one of a millimeter and if i move that down

3:26onto there we can probably just about see 0.1 of a millimeter

3:33so these dots are about 0.1 of a millimeter diameter now they’re 0.2 millimeter pitch so it begins to make

3:41sense that we’ve got dots there that are about 0.1 and 0.1 allows me to generate a picture

3:48at 254 ppi or 254 dots per inch

3:56now if we move off the dots we’ve got single dots there same sort of size and then we’ve

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

4:03got these dashes now the various size dashes we should find that the dashes are 0.1 wide

4:10and it’s much easier to see them we can see that they’re roughly 0.1 but

4:15what you can’t see there at that magnification is actually what’s going on

4:21there we go i think we might have found something there now first of all you can see right along the center there is a sort

4:28of a groove okay it’s not uniform all the way along but that is the very high

4:34intensity part of the gaussian focused beam and on the side here

4:41what we’ve got is something that probably i would imagine is like a

4:48an eruption from a volcano we’ve purged out the middle and we’ve

4:53blown it up onto the sides but what we need to do is just go in and

4:59look at that at a higher magnification and then you’ll see what’s actually happening now first of all we’ve got our

5:05deep groove and if we look in the bottom of the groove there’s a hint of what’s

5:10going on down there but when we come up to the top of the groove just there

5:20can you see all these bubbles that are existing along the side here

5:27now those bubbles do not exist in the background and they’re obviously

5:33also a different color so what’s going on

5:38well this is slate and slate started off its life as sediment in the bottom of an ocean

5:46sediment sand silicate of some sort anyway

5:55it gets compressed into a very dense material it gets subducted below the earth’s

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

6:01crust compressed so some fantastic pressures and then over millions of years it works

6:07its way back up to the surface of some sort of mountain or hill and gets thrust up above the sea level

6:15and that’s how they managed to dig slate out of the sides of mountains

6:21but the essence of it is it starts off life as a sort of a sandy silicate material and what do they make

6:28from sand and silicates glass what we’ve actually done here

6:34we’ve fused the material together and we’ve produced a glassy structure and that’s what those bubbles are those

6:41are bubbles in a gooey glassy material that we’ve created when we heated the

6:48surface up so that’s not a white powder that’s actually

6:53a completely permanent glaze gray glassy structure

6:59now there’s a classic example of a single dot and there you can see the bubbles of the

7:06glassy structure within that dot here we are on the fiber laser machine

7:11and we know that one micron wavelength light is basically not going to pass through

7:17this material it’s opaque and opaque basically means let me give you that simple analogy that i mentioned

7:24to you before that when a stone falls from the sky it’s completely harmless

7:30the only time it’s dangerous is when it hits you on the head and at that point when it collides with

7:36something solid you get an energy transfer okay the same applies to a light wave

7:43when the light wave comes down here only when it hits this solid surface will something happen

7:49and one micron waves are adequate to vibrate the molecules in the surface

7:56of this material and cause them to heat up so

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

8:01we know that the light is going to work on here can we get the energy concentrated in

8:08such a way that we can do my little dot test for example

8:14technically we should be able to do it because the focus on here is better than the focus

8:20on the continuous wave laser machine now that’s really the clue that gets me

8:28started on what the parameters should be for this machine now this is a 20 watt fiber laser and as

8:35i mentioned before we used about 20 watts when we were doing the

8:41test here and this little pattern just here

8:48so here’s the little dot program and what we’re going to try and do is to simulate the same conditions that we had

8:55over on the glass tube co2 laser so we’re trying to achieve that with a speed of 400

9:02power 100 percent the frequency here doesn’t really matter because we’ve got it set to a thousand but it’s going to

9:08be ignored because what i’ve done i’ve set the pulse width to one nanosecond now one nanosecond is a

9:15special code for this machine which basically switches on continuously as cw mode which is

9:21equivalent to the glass tube laser so we’ve got an equivalent set of conditions here

9:27for the 10.6 co2 laser and now we’re going to see if we can simulate the same sort of results on this fibre

9:35laser we’ve got a little pattern what we need

9:41to do is go and look at that under the microscope to see what we’ve got well here we are at 50 times magnification

9:47and we’ve got a scale here which at 50 times magnification shows that we have got

9:52a line which is roughly 0.1 millimeters wide so it’s doing roughly the same sort of

9:58job as the co2 laser it’s not getting any better i hoped it might be a little bit better

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

10:05but in fact let’s just have a look at the dots as you can see the dots are there but they’re pretty

10:11indistinct they’re merging into each other because the power down the center here

10:18has exploded so much that the glass that’s been created around the edge of

10:23the volcano has spilled over and joined the next dot it gives the impression

10:30that i’ve actually got too much power there at 20 watts and maybe i’ll be able to

10:36control these dots much better if i start reducing the power so this is a very good start previously

10:44any work that i’d done on this machine just by eye had been based on

10:50using one of the pulse widths that were available on this machine i hadn’t used this continuous wave mode

10:59well at 80 you can see we’re getting we’re still getting the glassy effect we’re getting slightly better

11:06separation of the dots they’re not spilling over quite as much as they did before

11:11and that’s 80 percent so let’s take a look what 70 looks like

11:20it’s getting a little bit better we’re seeing a little bit of better

11:25separation 70 percent let’s try 60

11:31still rather messy isn’t it they’re not really dots there are holes there but there are not clean dots

11:39let’s try 50 percent still a bit messy we need to go back and just remind

11:45ourselves so that’s what the co2 laser was doing

11:52i mean they’re not exactly 0.1 dots but they’re getting close they’re about 0.12

11:58because they’ve definitely got a gap between them but also they haven’t got a hollow

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

12:04center so maybe we could back off on the power even more or possibly

12:12lift the focus right up by maybe 10 or 12 millimeters so that we’re only using the tip of the

12:21high energy part of the beam so we’ve still got another couple of

12:26things we could try

12:42i think you can already see at those settings there is no comparison

12:49fiber laser is relatively rubbish in relation to the co2 laser

12:56the previous one was done at 100 power and 2000 millimeters a second

13:02because i don’t think the speed has any effect on it at all the pulses are still there

13:07at the same power regardless of the speed this is not like metal where you’re trying to build up the heat

13:13you just want the power per pulse and as we switch the beam on the power

13:19is there instantly we’re going to run this now at 30 percent power and see what effect that has

13:35we’ll give it one last shot at 60 power and we’ll go back to 400 millimeters a

13:41second just so that we can say we’ve given a fair comparative shot there is no point

13:46in coming onto this machine and doing it at 400 millimeters a second because i can do it on my other machine at 400

13:53millimeters a second so there’s no advantage to going down this route

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

14:03well yes it’s better [Applause] and if you didn’t have anything to

14:09compare it with i suppose you’d think that was quite good but when you see what the co2 laser

14:14can do this is still rubbish as we mentioned earlier just look at the definition of hairs

14:21all the fur on the co2 one what have we got on this one

14:29nothing just a bit of a blur now just in case you think i’m giving up too easily

14:36um i’ve also tried playing with the focus so those people that think they’re putting the uh putting the thing out of

14:42focus when they lift it up by two or three millimeters are sorely mistaken because look i’ve raised the

14:48head up in other words i’ve put the focus down below the focal point

14:54but this is not a reflective material so let’s not get too concerned and i’ve actually dropped the focus 22

15:01millimeters below the focal point by the time i get to here and yeah it’s it’s a very slightly

15:09blurred but we’ve still got sufficient power in the center of the beam to actually put a reasonable mark on

15:17this slate food for thought focus is not what you

15:22think it is stop it’s another day

15:27i’m older i’m grayer i’m fatter and i’ve had a thought i was just about

15:35to say that this machine can’t do this sort of work

15:40and then i it just doesn’t make sense it’s got all the capability to do the

15:46job but somehow or other it’s not giving

15:52i think in reality it’s me not understanding i suspect we have a little bit of a

15:58problem here number one i understand what I’m trying to achieve

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

16:05you might not so therefore what i’m going to do i’m going to take a break here and

16:12we’re going to go back to the beginning and try and explain to you the basic theory behind photo engraving

16:20on these laser machines because in essence it’s quite simple when you

16:26understand it but it’s a bit like riding a bike if you lift your feet off the ground

16:32you’ll fall over you need to do a bit more than lifting your feet off the ground many years before photography became available

16:40newspapers could only print text black ink on white paper this became a

16:47problem when they wanted to put pictures into their newspapers the only way that they could generate

16:54pictures was like this they had to get copper plate scribed and filled with ink

17:03so they could get their black ink onto white paper now that’s an artist’s job a very

17:10skilled job to do that so it was quite a few years before they managed to

17:16solve this problem and create ways of breaking up that picture from

17:23a continuous analog scale which went from very dark brown nearly

17:29black to almost white it’s a sepia

17:34it hasn’t got a complete black and white color range but it’s got a very wide color range

17:40there are just gradual changes of tone across the whole of the picture so somehow they had to

17:45break that image down into black and white now there are many many early attempts but eventually they

17:51came up with a process called half tone printing half tone printing allows you to break that picture down

17:58into a into a selection of dots this whole principle of half tone

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

18:04printing relies on your brain being fooled and filling in the gaps between the spaces

18:13it does basically a color mixing of black and white into various shades of

18:19grey within your brain so depending on the size of the dots

18:24that you’ve got in the black the black gradually changes to a sort of gray

18:31and then the gray the mid grays here change to white as the black gets less

18:37and less that is a very crude representation of what the half tone printing principle is

18:45the problem with that when we try and apply it to our laser system we’ve got small black dots and we’ve got

18:51big black dots now the only thing that we can do with the laser machine is make

18:57dark spots or we can burn something into the surface of a material we can

19:02only create one color generally now a couple of the large industrial type laser machines base their photo

19:10engraving software on this principle but it has a major weakness

19:16you can’t produce different size dots on a laser machine sounds pretty obvious

19:22doesn’t it but before we get on to the details of that this picture here

19:28although it’s an analog picture has been reproduced in modern times to go onto a computer so

19:34therefore it is no longer an analog picture and if we zoom in on this you can clearly see

19:42that it’s not completely analog it’s digital it’s made up of little

19:48square blocks called pixels and this is the modern way in which photographs and

19:55images are stored and used now isn’t that amazingly detailed what

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

20:00i’m going to do is we’re going to analyze this picture to try and illustrate several points first of all i’m in

20:07photoshop here and it gives me the opportunity to find out exactly how this picture is constructed

20:13if we take a look at the top here we’ll find that the picture contains a total of 21.7

20:18million pixels of those little squares that we just saw now you can’t see any squares on

20:25there can you if i zoom in there we go look you can see the pixels there at the moment it says this

20:32resolution of this picture it looks a stunning quality picture is

20:38300 pixels per inch i wonder what happens if i change that resolution to 10

20:46pixels per inch do you think the picture is going to get

20:51better or worse there we go

20:57trust me i’ve changed it i’ve cancelled it and we’ll come in and we’ll look at the image again image

21:04size 10 pixels per inch 21.7 million pixels still

21:12the same number of pixels that we started off with the only difference is if we look here

21:20at the width of the picture it’s now millimeters 8790

21:29millimeters eight meters wide and five and a half meters tall

21:36let’s just change that back to 300 where it was ah where is the eight meters gone

21:43it’s now 293 millimeters the very important point i want to make

21:48here is that pixels are not fixed elements a pixel can be as big as your

21:56imagination i could have a pixel that is a meter square

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

22:03you would see that picture from 10 miles off probably

22:08it would still have 21.7 million pixels but the pixels would be huge if you got

22:16up close to it you would not be able to see what the image was the bigger the pixels

22:21the further away you have to be to see the image so by that understanding if you’re only going to

22:28look at it at arm’s length you need a high resolution image but if you’re looking at as a billboard for example

22:34you could find that the pixels on a billboard might be one millimeter square if you walked up close to it so that’s

22:41important feature number one pixels are as big as you want them to be okay we will come back to that one

22:47shortly because that’s an important feature when it comes to deciding what we’re going to do with our images here

22:54we’ve got a colored image now we can’t work with colored images on our laser machine because

22:59we’ve already decided we’ve only got two opportunities we either burn or we don’t burn

23:06we’re effectively doing the same as an ink image black or white

23:13white is nothing and black is ink on a background

23:19so the first thing we’ve got to do with this image if we want to use it for laser printing is we’ve got to

23:26take away the color and turn it into something called grayscale okay discard the color

23:33information and now we’ve got a grayscale image now grayscale is an interesting point

23:40because unlike cpr images they run from black

23:45to white and there are no steps in between it’s all completely gradual with

23:52the grayscale system black is defined as number zero

23:59and white is defined as two five five well there’s 254 shades of grey between

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

24:05black and white so there’s a total of 256 colors in the range every one of these has a

24:12different color a different shade of grey each one of these little squares has got a different number attached to

24:19its color and every one of those pixels is mapped into something in machine memory in your

24:26computer memory although we’ve got individual blocks pixels there on that screen

24:32we can’t work with them because we can only produce black and no black i.e white

24:40there is a different sort of half tone printing it’s something called stochastic half tone which is basically

24:47random half tone this is patterned half tone printing where you’ve got a

24:52regular pattern and different size dots now stochastic half tone printing is exactly

24:59the opposite to that and let me just show you i’m going to first of all take this

25:05image and i’m going to turn it away from being a grayscale image into being something called a bitmap image

25:12now the resolution i’m going to leave it at 300 at the moment pixels per inch and we’re going to use

25:17something here called a diffusion dither we just say okay

25:22i’ve just destroyed the image well no i haven’t not really what you see there is something called

25:29an aliasing pattern it’s the mixing of the pixels that are in the background of the image

25:35with the pixels that are on the screen that you’re seeing as i change the magnification look it goes back to normal so if i zoom

25:43in now we’ll see what’s happened

25:50every one of these pixels that we can see here is either black or white we can now work

25:57with this on our laser if we just consider one of those lines across there look we can scan across there and

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

26:05here we are we can turn the computer on and we can burn a black line we can turn the computer off nothing on black line off nothing

26:13on off on off and that’s the way the image is sent down from here

26:20to your computer just a series of on off signals that correspond with the

26:26morse code that you see on the screen so it’s really very simple

26:31the problem is the size of that pixel what is it well remember what i said

26:38that pixel can be as big or as small as you want if i made that pixel for instance 100

26:45millimeters square could i print it with a single dot

26:51no obviously so in essence what we’re saying here is the size of the dot that we can produce

26:58with the machine it controls the resolution of our image the

27:05resolution of our image is controlled by the size of that pixel that single pixel there so

27:12if the smallest dot that i can produce is naught point one millimeters

27:20there will be 10 of those dots in a millimeter

27:26and there will be 254 of those dots in an inch so therefore what i’ve now

27:32got to do i’ve got to come back to this image and i’ve got to set the image size to

27:41254 now it won’t change anything on this screen

27:47but what it does it changes the physical size of the pixels and it will actually change if we take a

27:54look again and if we look again you’ll see that first of all it’s changing the number of

27:59pixels and the resolution is 250 poor 254

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

28:05but the size of the image now is 219 by 346. now

28:12if we don’t want an image that size then we’ll have to change it

28:19so now i could if i wanted to click these boxes to constrain the image and let’s just say i wanted an image

28:25that’s 100 millimeters wide 120 millimeters wide 120.

28:32there we go so i’ve got 120 wide 75 millimeters tall and it’s still got

28:38254 pixels per inch i have not changed the resolution of the picture

28:45okay and you’ll notice the number of pixels has now dropped even more

28:54and that’s an image which we can print because a we can produce dots that are

29:000.1 millimeters diameter and b it’s a size that we can get onto

29:07the machine okay so what you’re looking at here is a

29:12very crude representation of my little dot test pattern

29:19now it’s been very carefully designed this test pattern for several good reasons first of all i want to be

29:25able to visibly quickly check the size of a dot estimate the size of a dot

29:31so i’ve made my pixels here not 0.1 millimeters wide the gap between the pixels is also 0.1

29:40millimeters wide so that’s effectively a black pixel a white pixel black pixel white pixel

29:48like that so all these are black these images that i’ve got on here the

29:54way your laser interprets these is very simple it comes along here and it gets to this

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

30:01point just here and it switches the laser beam on and it draws a burn line until it gets

30:09to here and then it switches off because when there’s white

30:15there’s no laser beam on off on off the same applies to

30:22all of these they’re all on for black and off for white but there’s a fundamental

30:27problem here we can’t first of all manufacture square pixels

30:32with our laser we can only produce round burn dots and there’s another problem

30:38when the laser comes up to this point here it says switch the beam on which it does

30:43instantly but of course we’ve got a round dot it gets to this point and it says switch

30:50off but again we’ve got a round dot here here on

30:58off on off now it might not seem too much of a

31:03problem to you along there because there’s still dashes but hang about that dot

31:11is half a pixel hanging off the end and we’ve got one pixel gap here so if

31:19i’ve got half a pixel there half a pixel there half a pixel here

31:24and half a pixel here like that with my dots

31:33then how much gap have i got between the pixels

31:38um that’s a problem because remember how the brain is working it’s looking at the overall color of the

31:44background which is white and it’s looking at the overall color of the foreground which is black

31:50and it’s mixing those two together in your brain so the more white in the image

31:57the lighter the gray you will see and the more black in the image the

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

32:03darker the image will be do you see the problem we’ve lost our

32:09white between the pixels so we’re automatically when we’re doing

32:14photo engraving where we’ve got lots of these pixels sitting very close together we’re automatically going to create a

32:21dark image and that is why you will find with every single piece of photo engraving software

32:29there is a fairly significant chunk of lightening or brightness control involved to try

32:36and enhance the image and reduce this effect i have to admit to being

32:43slightly very slightly involved with some of the early development work in another piece

32:48of software called light burn very clever guy

32:53designed the software and he’s done a fantastic job of replacing virtually every part of rd works and

33:00making it five times better than it ever was with all sorts of extra features

33:06he identified this problem and decided that the right thing to do would be to delay the start

33:14of the beam so he shifted the start of the beam along and finished the beam half a pixel

33:21early and half a pixel late so that now

33:26you get the start and the finish of your pixel at the right place the problem is

33:33when you subtract half a pixel off of there and half a pixel off of there

33:38you’ve got no pixel so you get no dot and that was a fundamental fault

33:45with his logic everything that was a single pixel

33:50disappeared and it changed the quality of the image

33:56completely the opposite way to what was intended you will always have this issue and you will always have to

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

34:02lighten your picture now this 0.1 dimension for this pattern has been very carefully chosen based on

34:10what we could possibly achieve on a co2 laser with the lens system there you can get

34:16less than 0.1 dot under certain circumstances with certain materials but in general

34:21the smallest dot you’ll be able to burn will be 0.1 and therefore the best resolution that

34:29you can create your image at is 254

34:34ppi which is a 0.1 resolution pixels per inch

34:41equals 25

34:460.4 millimeters so if we’ve got 0.1 it means we’ve got

34:5310 of these pixels per millimeter so if we multiply 10 by 225.4 we get

35:00254. so that’s how we arrive at these numbers now good quality photographs are

35:06typically 300 pixels per inch

35:12the essence of what we have to do to copy that photograph is to make sure that we have dots

35:20that are 0.1 so we can get 254 dots per inch so that we can immediately

35:27copy every pixel with a dot that’s a very key part of photo engraving you can’t

35:35make the dots bigger than the pixels because if you do they will overlap like this and they will occlude

35:43the background which is the thing that’s giving you the impression of light and dark you

35:49change the density and the color of your image

35:55i did say that it was very simple and i did say that it was very complex this is the

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

36:01complex part this is the simple part very simple one dot equals one pixel

36:09so look at the other way around decide the size of your dot and that will tell you the resolution of

36:15the image that you can reproduce pixels do not overlap on the screen

36:21therefore you cannot have dots overlapping on your material

36:27now i did say that i would come back to this image here which as you can see it quite small you

36:32can see that it runs from black grey through to white and we did say that some of the big companies use this

36:40idea for their photo engraving it’s quite economical on code

36:47but it’s not particularly pretty as an end result it gives reasonable results but not

36:53quality results in my personal opinion there are people that claim they can print

36:58a thousand dpi now a thousand dpi

37:03means we’re going to have a pixel or a dot size of .025

37:10that’s about the thickness of a human hair that’s pretty incredible nobody in the

37:16normal world can produce dots that small with an industrial laser machine or even one of these hobby laser machines

37:24the best you’re going to be able to do is probably 0.05 which is probably close on 500 dots

37:30per inch but let’s just assume that they think they can do a thousand

37:36dpi well if this is a if this is one dot you won’t see it

37:42three or four dots then you might see it because what happens is it’s going to take a huge amount of time

37:48at a thousand dpi because what happens is you’ve got a thousand dots across this way

37:54and therefore you must have a thousand dots down that way because this is a square pixel

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

38:01and a thousand lines this way is going to take absolutely ages to scan backwards and forwards these

38:08blobs will be built up from these very very small dots that they supposedly can put down

38:15so it’s going to take a huge amount of time to scan across this image but very very quickly we’ll just zip

38:22back to this lovely image here which is the grayscale image now it is

38:27possible to try and work with a grayscale image depending on the material that you’re

38:34working with for example an organic material such as wood or leather has got a

38:43scorching range from very light scorching to burnt dark brown

38:51so there is a color range that you could exploit to try and match the 256

38:59shades of grey that are in this image and what that means is instead of

39:04putting dots down dot dot dot all of the same intensity what you would

39:10try to do is every time you moved across a dot you change the power

39:16in the pulse so it is possible to do grayscale engraving as well

39:25but it’s nowhere near as clean neat and efficient from everything that

39:32i’ve tried and tested as proper dithered binary engraving

39:39but i thought i’d just mention that hey that’s not the be all and end or what we’re trying to achieve

39:45but of course on things like slate where we’ve only got one color gray

39:51and a background which is dark grey if you’re using acrylic you produce

39:57white on a clear background so what i’m saying is there are many

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

40:03materials around which are what i call binary materials they’ve only got two natural colors

40:08anyway it’s only the organic materials where you’ve got a possible color range that

40:14you can exploit to produce grayscale engraving right back at the machine

40:20let’s try and make some sense of what we have observed earlier under the microscope now i was trying to

40:27run at 2 000 millimeters a second because as i said to you this machine is incredibly

40:33fast at the way in which it builds up its pulses unlike the co2 the pulses will happen

40:39instantly to travel one millimeter takes roughly half a millisecond

40:45and that’s just a starting point to make life mathematical life nice and simple a little bit later on

40:52we’ve got a two nanosecond pulse now that means we’re going to get a

40:58pulse every roughly micro second i know it’s 850

41:03rather than a million pulses a second but hey let’s not argue too much about that amongst friends for rough maths it’s good enough

41:10to say a million pulses a second now our pixel is only 0.1 millimeters

41:17wide it might only be 0.1 millimeters wide but as far as this machine is concerned

41:23it’s a long line it’s a line that is 0.1 millimeters long so how long does it

41:30take to travel 0.1 millimeters the answer is

41:350.5 milliseconds divided by 10 because there’s 10 of these in a

41:41millimeter so that means it takes 50 microseconds

41:46to travel one pixel but we’re producing a million pulses a second so therefore it’s

41:54burning 50 times across that 0.1 millimeter pixel but we’ve already

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

42:01determined from our observations under the microscope that when we fire the laser at this slate

42:09it produces a little volcano which produces when i say a burn spot i mean a damage

42:15zone of 0.1 millimeters that’s a rather familiar number 0.1 millimeters that’s the size

42:22of a pixel but hang about we’ve just talked about that 0.1 pixel

42:28with a 0.1 dot means it’s going to stop and hang over the end of each pixel

42:35by half a dot and isn’t that what we observed we observed all the dots joining up

42:44so we’re never going to win with this approach because we’re always going to have this

42:51half a pixel overlap it doesn’t happen on the co2 machine for various reasons the most obvious is the

42:58fact that we don’t get this first half dot overlap because there’s

43:03always a delay in the pulse build up something that i’ve noticed a long time ago and never had any occasion to use it

43:10want or if you like be curious about it is something here called drill mode now that sounds

43:19interesting doesn’t it drill mode i’m wondering if i’ve got any control

43:25between drill mode we’ve got 0.1

43:30milliseconds set by default milliseconds that sounds like

43:38years in terms of the response speed for this machine

43:44so yeah i thought well maybe 2 000

43:51yeah 2 000 millimeters a second how long a pulse do i actually need

43:57and i played with the numbers and i finished up with something like .0005 or something like that

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

44:03some some stupid number of milliseconds

44:08did it work no absolutely nothing

44:14[Applause] back to the drawing board that was a dead end

44:21not wishing to give up on this i felt that somewhere on this machine there must be some way

44:29of doing what i need to do drill mode seem to offer the most

44:37likely possibility so i went to the manual and tried to understand how

44:45drill mode worked now the good news is

44:53it’s something to do with scan mode which is great so it’s not mode on its own

44:58you can actually use it with scanning and here it is 0.1 default

45:06milliseconds select this mode to define in microseconds

45:17hang on that said milliseconds

45:25now it begins to make a bit more sense i was putting such a short pulse in that

45:32i was getting nothing out so if it’s actually micro seconds

45:37i was putting in like nano seconds of pulses which are not going to do me any good at

45:44all because they’re not repetitive they’re just once

45:50well how once are they

45:57select this mode to define in micro seconds how long the laser is kept on for each point

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

46:04of the image that is marked i wonder what that means that sounds

46:10very chinglish to me

46:15and then we come on to the obvious some materials require longer and shorter exposure times to achieve good marking well yeah

46:26increasing the drill mode time will sometimes create a deeper but lower resolution mark hang on

46:34lower resolution prolonged drill mode times will

46:39significantly increase the overall time required to complete the mark so

46:46that seems to imply that there’s no relationship between speed and drill mode

46:53i can specify two thousand millimeters a second but i’m not gonna run at two thousand millimeters a second i’m going to run

47:00at and here’s where i think the trick comes in look

47:08fixed dpi well i’ve already got the dpi fixed for my images

47:13i’ve fixed in x 254 because that’s the image i’m fixed in y

47:20254 because that’s what my image is

47:25so i think with a nearest bit of luck when i now interpret

47:32this this is what i think i’m going to get

47:42i think by specifying 254 ppi which is a fixed interval in x and 254

47:50ppi fixed increment in y i’m actually defining my pixels to sit

47:57on a grid like this and if

48:02my pixel sits on the intersect of one of these grids and is black remember what black does

48:10black turns the beam on so if i specify a duration time

48:15for drilling i’m going to get

48:20at that intersect a drill hole and then i’m going to get another drill

48:27hole there and there and there and that means when i get a

48:33single pixel i’m not going to get a lump out at the end i’m going to get a drill hole at the intersect point

48:42wow now this is looking very very i’m getting quite excited now is it too

48:48good to be true let’s give it a try i presume that the

48:53pulse and frequency numbers are still relevant to the

48:59drilling pulse itself so if i specify a two nanosecond pulse i’m going to get a pulse every

49:05microsecond just one two nanosecond pulse so if i

49:11specify one microsecond i’m only going to get one two nanosecond pulse

49:18and hopefully it’s going to be one two nanosecond pulse right in the middle of a pixel well as i’ve said to you

49:24before ah this is not a tutorial this is you looking over my shoulder

49:32and either falling flat on my face or succeeding so let’s push the button and see what we

49:41[Applause] get

49:47something silly for a minute because i think i’ve got to go the wrong way i think i

49:52want to go shorter time period but i’m going to go a longer time period just to prove a

49:59point [Applause] to starting

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

50:06wow yes you see it took a lot longer

50:13so it’s not speed related it’s duration of pulse related


50:25you will absolutely love this when you see it under the microscope

50:30now we’re going to go the other way

50:37[Applause] 1.5 straight to point one let’s do that just

50:44go too far right down to point one micro seconds

50:54now that was quick to be honest what i can see here is really exciting

51:02[Applause] certainly quick again

51:11and look at those under the microscope now because they are far too interesting for me to keep to

51:16myself here’s what 10 micro seconds of drilling

51:22looks like now do you believe that this process produces glass is there any more

51:28proof that i need look at it

51:41in fact i accidentally touched that with the microscope and look i’ve cracked the glass okay now let’s take a look at

51:48the next one which was one microsecond

51:54okay now look we can see the set of holes along the dashes there

52:02they’re literally just piercing holes they’re not running along continuously

52:08wow you see at one micro second we’re starting to see the dots but

52:14they’re still squirting out enough glass so that they overlap

52:19we’re going to go down to 0.5 microseconds

52:27and the dots are a lot cleaner

52:36now we’re getting a bit of separation between them look

52:42we’re still squirting out too much from the little volcanoes

52:49so we’re still putting too much energy in let’s go and look at the point

52:56one microsecond everything is getting a lot neater isn’t

53:01it look we can see every one of those pulses along the dashes here

53:09i mean it clearly indicates that we have got drilling taking place at the coordinate intersects

53:17as my drawing indicated wow look at those they’re lovely dots

53:23aren’t they well now i say they’re lovely dots there is a problem with them actually

53:33they’re nice size and they’ve got a nice white edge to all those dots they’re

53:40lovely and separated they will produce a great image i’m absolutely sure about that

53:46in fact i’m sure it’s going to actually beat the quality of the image that i get from the co2 laser

53:55but and there is a butt

54:01look at this can you see that there

54:06a black hole it’s a donut but it’s not a white doughnut it’s a

54:11black doughnut now remember the way in which the whole of this principle

54:19of photo engraving works it’s the relationship between white

54:25and black so here we’ve got a background

54:30and here we’ve got if you like a white foreground but we’ve also got some black background

54:36showing you no no no i know it’s not the background but it doesn’t matter what it is it’s black

54:42so it’s adding to the blackness of the image

54:48so it’s actually going to downplay the quality of the result that we get

54:53it’s going to be a slightly dimmer result now i don’t

54:59i didn’t realize that when i was looking at them under the magnifying glass but we also did a

55:05couple of other trials and i might have to go and do something did i do i changed the power didn’t i to a different different power setting

55:14yeah no that’s not going to work is it because look i’ve got even bigger black holes in there

55:20[Laughter] now i know this is a very minor detail

55:25that probably most people wouldn’t even bother to think about but it is an important part of viewing

55:32these images it’s something that i’ve become very very aware of and those holes are just unacceptable

55:38there’s all black and no white decreasing sorry by increasing the pulse length i’m just making the hole bigger and the

55:45squirt the white glassy effect less so let’s just move on to the next one

55:53which was a 2 nanosecond pulse but at 80 percent power

56:02now will that reduce the central black part well

56:10it certainly looks as though it’s having an effect but has it made them so

56:20and looking at those you know i think they are less than 0.1 in fact i can see they’re less

56:27than 0.1 they’re probably somewhere in the region of about 0.08

56:32one inch is 25.4 millimeters 25.4

56:38divided by 0.08.08

56:43equals 317.5 i might set the resolution to 300 and

56:49see what we get well i’m extremely pleased with that result and

56:57yeah okay egg on me face i thought it was going to fail it hasn’t it’s come up trumps so let’s

57:04go and do the real test which to see what the image comes out like in comparison

57:19well that’s probably about half the time that it takes to do on the co2 laser

57:25even though i’ve got my co2 laser well pimped up and i thought it was doing

57:31very well this is doing a superb job it’s really quite interesting that

57:36when you look at the actual door mouse itself it seems to be slightly darker than this

57:44one which one do i like it’s very difficult to choose between

57:50them to be honest this one’s slightly whiter dots in the

57:55center of the little spots that’s what i think is making this

58:01one darker but it’s still a lovely image

58:07well i think we’ll finish on that happy note should we i think we found the secret of um

58:13engraving slate on the fiber laser drill mode thanks for your time and

58:19patience and um I’ll see you on another adventure next time bye for now

What Next?

Did you enjoy this post? Why not check out some of our other posts:


Last updated April 25, 2024


The information provided by n-Deavor Limited, trading as Laseruser.com (“we,” “us” , or “our”) on (the “Site”) is for general informational purposes only. All information on the Site is provided in good faith, however we make no representation or warranty of any kind, express or implied, regarding the accuracy, adequacy, validity, reliability, availability or completeness of any information on the Site.


The Site may contain (or you may be sent through the Site) links to other websites or content belonging to or originating from third parties or links to websites and features in banners or other advertising. Such external links are not investigated, monitored, or checked for accuracy, adequacy, validity, reliability, availability or completeness by us.



The Site may contain links to affiliate websites, and we receive an affiliate commission for any purchases made by you on the affiliate website using such links. Our affiliates include the following:

  • makeCNC who provide Downloadable Patterns, Software, Hardware and other content for Laser Cutters, CNC Routers, Plasma, WaterJets, CNC Milling Machines, and other Robotic Tools. They also provide Pattern Files in PDF format for Scroll Saw Users. They are known for their Friendly and Efficient Customer Service and have a comprehensive back catalogue as well as continually providing New Patterns and Content.
  • Cloudray Laser: a world-leading laser parts and solutions provider, has established a whole series of laser product lines, range from CO2 engraving & cutting machine parts, fiber cutting machine parts and laser marking machine parts.
Item added to cart.
0 items - £0.00