r/Optics • u/LASER-RASTERIZER • 6d ago
So I’ve been toying with one of my lasers
hey everyone, sorry for the long post, I’m hoping some of you can help me understand this better.
I have been building a personal app for converting raster graphics into mopa laser color engravings by vectorizing and mapping to my saved pre tested settings based on the image color and creating the project
and while doing so added some features for converting images to cells of diffraction gratings that I then laser onto stainless steel and it results in a sort of multi color diffraction effect similar to but absolutely not a hologram, I’ve been calling them fauxlogram engravings for lack of a better phrase/word.
dont worry this isn’t an add or me trying to have people try my app, its just back story for my question so you understand where im at and how I got here.
over time I’ve extended the processing methods to where I can sort of control a gradient that gets applied to the way the fauxlogram engraving (I’m calling it this until someone gives me or I find a better name because it’s easier to say than describing the full look) is made, leading to some pretty cool looking engravings that do some pretty wild stuff in the right lighting.
im trying to learn more about exactly why / how this is working because to be honest I sort of stumbled onto it accidentally and just keeping poking around trying various different ways of processing to see how it affects the result.
some changes give awesome new realms of control over the flow of the color changing, and get adopted permanently.
others changes are a disaster that I have to revert
sometimes I don’t know a change was bad until several changes down the road reveal the change wasn’t good for some reason like forcing outputs to be more similar/smaller range of useful control in some not quite edge case scenario, or just what I thought it would change didn’t change the result how I expected.
I would much rather base my changes on more than a gut feeling and caffein, so I don’t waste so much time going down dead ends.
I’ve taken it as far as I can without properly understanding the diffraction effects and involved principles.
the reason I am posting in the optics sub instead of a laser sub is because I’ve done a lot of looking around in the laser scene and no one fully seems to know what’s going on much more than where I’m at with it, or if they have they aren’t discussing it in placed I’m able to find.
One guy who’s work inspired me , has noted that a laser moving at 300mm/sec pulsing 300khz (just magic setting on his laser) equates to a pulse pitch of 1 micron, and suspects this has something to do with the effect, I get the kind of effect this person talks about at slightly different settings that result in a 1.14 micron pitch. Neither of us seem to know if this is the magic behind it.
however, I’ve noticed that with my particular processing the effect is much more pronounced than other similar laser engravings I’ve run into online.
the gist of my process is for every color in the source image (let’s say 20 different colors), I make a copy of my magic “fauxlogram looking setting” to a layer in the design software, then I keep the frequency constant but modulate the speed the laser head moves at proportional to the color spectrum red to violet so that the pulse pitches being generated for each different layer vary from maybe .5 micron to 1.5 micron give or take. based on what color each layer represents, then I sort of overlay a gradient of values 0 through count of layers, expressed as an array of x, y intensities … aka an image/pixel array this image has its brightness mapped to a number up to the layer count and then the diffraction gratings get their layer rotated based on that gradients values , basically switch which of the speed modulated settings layer draws the diffraction lines in that section, going in order from highest to lowest or lowest to highest speed… this becomes visible as a literal gradient in the fauxlogram engraving
sorry I know that was a lot, but I wanted to explain basically what appears as a gradient in the fauxlogram diffraction effect is achieved by switching the speed the laser is using according to a gradient overlay so the pitch is either getting closer together or further apart according to the gradient/image brightness in that area
now where I could use this sub‘s lovely members help is in understanding this phenomenon better so that I can hopefully gain more control over it.
i don’t know if the color is influenced by oxide growth on the metal or if it’s entirely just the shape of the laser dots place on the metal.
I know that if I lower the power just a little bit the color changing goes away and I only can see the gradient in the brightness changed as it still shimmers in the light but doesn’t change color
i know that if I move the central speed much higher or lower than my magic setting with the base pulse pitch of 1.14 micron the effect diminishes almost fully very quickly
i rotate the angle of the parallel lines in the cell ( the diffraction gratings) based on the brightness in the source image, the angle of the gratings definitely seems to impact which angle a light has the brightest and dimmest look on the surface, and speed of laser seems to cover the color change from my observations.
so far I’ve been able to get the gradient to appear as a radial gradient expanding from the center or contracting from the edge, as well as left -right and up-down gradient … think like stripes equidistant where each stripe color shifts by some ammount , this was initially added to be a viewing correction so that parts towards the bottom would appear the same color as parts toward the top, since they are at different angles from each other and the viewer when viewing, so the color reflects/diffracts different because of that, thus shifting the color in the drawing to compensate
when I applied extreme values to the gradient is when it became a creative effect rather than a subtle corrective effect.
so now I would like to be able to get more control over this effect but I honestly don’t understand it enough nor have the vocabulary to effectively search and learn enough to better control it, or maybe it’s one of those things where this is as much control as one can get and I just need to get some better artistic ideas, I’m open to that being the answer if that’s the case.
so I was hoping some of you guys might have a good idea of what is going on here, and be able to point me toward some good entry level and maybe mid level reading resources that might help me better understand and thus better control the effect, or even if you just have some vocabulary that would make my search easier that would be greatly appreciated too!
if this is an inappropriate post here please remove it, I’m just wanting to understand the optical effect I’m seeing in these engravings better so that I can hopefully control it better. I started seeing this sub in my feed after posting some fauxlograms previously so I think maybe the algorithm thinks this is the right place for the discussion.
I’ve attached some video samples of the engravings showing this effect and would be grateful for any details anyone can provide
if it’s helpful I could post some low quality microscope shots of the surface, I’d have to track down my scope but it’s around here somewhere.
if you have made it this far I appreciate it and hope you enjoy viewing and even theorizing or analyzing what is going on in these engravings, and to anyone who can reply with some good info, I wish to thank in advance
https://reddit.com/link/1wzmvcw/video/vsfilj1lnyth1/player
Radial gradient for every shape in the artwork
Moth image superimposed over moth pattern as gradient input
Radial gradient scope over the whole image instead of per shape
3
u/SpicyRice99 6d ago
I did not read the whole thing, but that's pretty cool, OP. I'm curious does the grating hold up to daily wear and tear? If not maybe it eventually need a clear coat?
1
u/LASER-RASTERIZER 6d ago
It holds up surprisingly well, I think it’s just so fine that it can’t really get damaged on anything because it’s like microns deep it feels almost smooth to the touch like it’s just subtle textured that you can barely feel if you rub it in the back of your finger nail if you get what I mean.
I’ve got stacks of test runs that I handle regularly without care and they stay looking good, I don’t have any older than like 6 months or so , so I can’t say to how they hold up over longer amounts of time yet, but so far so good
1
u/SpicyRice99 6d ago
I see, nice. For basic theory I recommend Fourier Optics bu Joseph Goodman, there's a section on holograms near the end. Ditto on more applied theory, try arkiv or libgen
1
u/LASER-RASTERIZER 6d ago
I’ll check it out, it’s difficult finding stuff about fauxlograms compared to holograms so far , there are similarities but not much actual overlap in technique from what I’ve found, still useful info and usually if a source is into hologram they are also into other related stuff, so I’ll be checking these out, thanks
1
u/SpicyRice99 6d ago
No problem, you can find the PDF on libgen btw .
Also, I'm still not entirely sure what you are defining "fauxlograms" as...
1
u/LASER-RASTERIZER 5d ago
Neither am I to be totally honest lol
Like the images/videos attached where the viewing angle changes the perceived color in a manner where the color appears as changing gradient based on viewing angle… but the real test is kind of famously “you know it when you see it”
When I show them to people who aren’t familiar with actual holograms , they call it a hologram because that’s the closest thing in their memory/awareness to its appearance they are familiar with, that’s kind of where the naming came from because I got sick of correcting people when they ask me how I make the hologram/holographic engravings, faux + hologram/ holographic = fauxlogram/fauxlographic
It’s just been easier communicating the concept with one word + imagery of the results showing the movement perceived from lighting or viewing angle change vrs explaining to people the exact make up of the engravings which are just tons of cells of parallel lines between .08-.04mm line interval (could be different, this is what works good on my laser setup) where luminance maps to the angle of the diffraction gratings and color maps to laser speed and thus physical pulse pitch thus perceived color that results from the diffraction from the pattern indented into the metal
It’s not some super strict definition though, in my mind it’s anything that people who don’t know properly confuse as a hologram, iridescent markings that show movement and change color to multiple hues qualify in mind, though I haven’t seen many other mechanisms used to make engravings like these via different methods, but to me if it’s reminiscent of but not an actual hologram or 3d light wavefront reproduction, I’d consider it a fauxlogram in this context… probably more accurate to call these diffraction based designs or some such thing , but so far not people I’ve used the term fauxlogram with just sort of get it when they see the imagery and hear the term side by side, so that’s kind of the story/explanation/definition I’m operating on
1
u/SpicyRice99 5d ago
They just look like diffraction gratings with slightly different parameters to me. You probably don't even need pixels, you could do it continuously.
2
u/LASER-RASTERIZER 5d ago
You are 100% correct, It doesn’t need pixels/cell groupings, they just make the effect much more dramatic and visually interesting, I started out initially where you are suggesting I could probably go, and evolved to where things are at now through experimentation. Now I would like to learn why simply grouping the grating carriers into cells transforms it so much compared to not grouping into cells, among other aspects, so that hopefully I can manipulate the visual effects more specifically and more efficiently.
I feel like I’d have saved 6 months if I knew anything about visual optical phenomena when I started playing with this stuff , then again it’s been a blast exploring without any understanding or bias, I’m happy I started this way, but it’s time to start working towards understanding instead of experimenting.
1
u/mr-rogee 6d ago
This is really cool. I've been dabbling in something similar, but with photography. An AFM (or maybe confocal microscope) would let you see the microstructure. Then maybe you could model it with rigorous coupled wave analysis (RCWA). I've played around with inkstone for this purpose in the past.
For learning more about this topic, I've found this channel to be helpful: EMPossible thats an RCWA video, but the channel also has more videos on introductions to gratings, diffraction, etc.
2
1
u/Technical_Island_851 5d ago
These are stunning. Would this technique work on non-ferrous metals? Imagine the patina on an oxidized copper surface 😍
2
u/LASER-RASTERIZER 5d ago
Thanks. I think it may work to some extent on other metals, but I’ve only done testing and experimentation with stainless steel, I think there would be different optimal settings but the process in theory should work to some extent I think as long as the metal isn’t so soft that it can’t achieve the same type of structure it should work to some extent.
Took a lot of settings experimentation to develop the exact repeatable effect with stainless (I probably have some 800 business card sized blanks in stacks all over the house from testing to get here with stainless), I’d probably need equivalent to tweak the settings for copper or brass or another metal, and I’ve still got a lot more exploration to do on stainless before I move to other materials eventually like copper or brass or titanium, I will eventually get there but I prefer to fully explore a material before moving on
I’ll definitely post online once I get to other materials but not going to lie I’m still a long way from ready to branch out so I don’t think I’d even say “follow me to find out” just yet because I’ve got so much more on my plate prior to getting to that point
1
u/Technical_Island_851 5d ago
Wow! Would love to see all the mishaps and experiments too if there are that many. It’s such a cool project, can’t wait to see more 👏🏼
1
u/LASER-RASTERIZER 5d ago
I’ll try to post some picture of the scrap piles in a way that lets you see the good, the bad, and the ugly at some point, right now though there is no way to capture a picture of much of them without revealing how terribly messy and cluttered my house is at the moment lol
I started a subreddit called MOPA_LASER_RASTERIZER that I will be using as a sort of video log of sorts so that I have a place I can spam with the pictures and notes and videos of what I discover along the way, it also will double as a place for users of the app I’m doing this with can discuss and seek assistance, but right now I’m pretty much the only user, I suspect it will stay that way because it’s a convoluted app that requires the stars to align for a user to be in the target demographic of laser owners with tenacity and curiosity to figure it out… so the subreddit will probably always just be me posting stuff there as a log lol
Might be a good way to follow along, very empty right now though. I’m not good at social media-ing or social anything lol
1
u/Technical_Island_851 4d ago
Already joined 😏
I’m totally new to lasers but I use 3D printing and CNC via FreeCad and work with various metals in my projects. Is a laser such as the one you use with the app you’ve created way above the pay grade of someone looking to try it out? Have you significantly modified any hardware to achieve this? Thanks
2
u/LASER-RASTERIZER 4d ago
My laser was around 3500$
I could have got something that would have been fine for this kind of stuff for around 1200-2K$ I think, but I can’t be sure because I have only used my setup, but I’m only using 30% of the power of my laser to do this work, so I assume a laser 1/3 as powerful could do it at 100% power
But I can’t say for certain.
So it does take an initial up front investment, but it’s not huge, and if you really want to get into it , it’s doable. I bet there is a good used market toobecausr enthusiast upgrade and get multiple lasers and then move on to other ones, though I would be weary of buying used.
You need at a minimum probably a 30 watt mopa fiber laser (1-2K$) (I use 100watt at 30% power), need lightburn (100$),
Has to be a mopa so you get the high variability of frequency and pulse duration settings, normal fiber lasers (q-switched) have less options or are set at a specific freq or pulse duration often., and this whole effect requires kind of honing in to the setting that produces the pattern that causes the diffraction to occur
You may have a shared space in your community with lasers you can use after taking safety training and paying member fees , look for any makerspaces or hackerspaces in your area with fiber lasers on the equipment list, might be most affordable way to test the waters
Edit: no hardware mods at all, I saved money buy buying an import from China with zero after sales support, an equivalent laser from a US company would have been twice what I paid
1
u/Technical_Island_851 3d ago
Thanks so much for the info, I will take a look at mopa fibre above 30 W. I’m wondering if I can get one that will fit my cheap CNC? Is your app available on git? Thanks 🙏
2
u/LASER-RASTERIZER 2d ago
Yes, the project is called mopa-laser-rasterizer, but it’s not really one you can clone the repo and run locally as it’s baked into needing aws infra and services as that was how best to keep it cheap and usable by non technical people. the readme in the repository has the links to the site and documentation though so it’s a good way to find it without me pissing mods off by posting urls.
1
1
u/timstrumentality 5d ago
Wow, I wonder if this could be used in watchmaking, as an alternative to Guilloche.
1
u/LASER-RASTERIZER 5d ago
On thin metals intricate designs can warp the material as the process is intensely hot but rather fast so usually it’s cool enough to touch a couple seconds after finishing the piece… even so, I’m still often dealing with warping depending on the thickness of material and intricacy / sparseness of the design.
At .8mm thickness material it wouldn’t be much warping over the distances involved in watches, and at lesser than .8mm the metal itself is already pretty flimsy and almost malleable itself, so I’d assume the warping would be a non issue in a proper manufacturing setup.
As a watchmaker I’d assume you would probably be well equipped for figuring out a solution to prevent any significant warping
1
u/Padrepapp 5d ago
Before anything, that is just really cool and awesome!
I would definitely try to pinpoint if the effect comes from the gratings or a possible thin oxide layer making interference. Not sure where you are located, but if you have a local university, they might have a White Light Interferometer (sometimes called coherence scanning interferometer). This could give you an exact measurement for your grating pitch, peak to valley, grating orientation. If they have an ellipsometer, they could answer the oxide question.
If not, you could reach out to some WLI/Ellipsometer manufacturers, try looking for optical engineers working at these companies on LinkedIN, and reach out to them, if they would be willing to measure your samples.
1
u/Padrepapp 5d ago
could you try and make a really high groove density grating with high power? I wonder if you could try only making an oxide layer with the laser, and see if you see the color effect with no grating present, but the sample being blasted with the laser.
1
u/LASER-RASTERIZER 4d ago
I also do a lot of oxide based color engravings without involving diffraction gratings, those just stay a static color or occasionally may be iridescent , but without all the movement. Most of the time it’s a really nice looking engraving
If you look through my post history you will see a “lifecycles” series of posts which are mixed oxide color and diffraction grating based color engravings showcasing the lifecycle of various animals / plants / fungi
They are really fun to do
The thing though is … the actual diffraction gratings ARE coming from the laser settings themselves, the diffraction grating is created from the laser pulsing at its 350khzand then moving at 400mm/sec…. That is what generates the diffraction gratings themselves.
The parallel lines in the cells of the engraving are not the gratings themselves but the carrier of those gratings, each parallel line is a field of microscopic gratings caused by the pulse pattern and speed of the laser.
What my processing does is just modifies the manner in which those lines of diffraction gratings are drawn, selecting which of the 30 laser settings to use (starting with the above described freq and speed combo but then adjusting speed so the gratings are clos the the original color in the image that carrier is meant to represent) when lasering each part of the image basically, shifting the speed and thus pulse pitch/grating size based on where in the artwork it is and the input gradient passed in to control it.
Changing anything other than the laser settings won’t change the diffraction gratings themselves
So it’s not something I can separate while still keeping a like comparison.
I can do the test but instead of not using diffraction gratings I could not do the additional processing of the image, in that case it’s still a iridescent mark that looks cool but it’s much more static and any movement just sort of blurs out into a softly blurred color image rather than something so, for lack of a better word, staccato, if that makes sense?
The moment I change the laser settings from this baseline though it might as well be a completely different experiment .
But maybe it’s just as useful of an experiment to use laser settings that don’t produce this amount of iridescence as the starting point and run it through the same image processing and see if the result reveals any more useful information… I hadn’t really thought of doing that before, thanks a bunch for the idea :)
1
u/LASER-RASTERIZER 4d ago
This is a great idea
I know the pitch the gratings are instructed to be, but no idea on the depth or any blur/slope , or how physically accurate the pattern produced by the laser actually hitting the material are
There definitely is some amount of oxide formation, but there is also definitely physical pitting on the material too as well as microslag /dross on the surface.
I suspect it all contributes to the effect, but I’d love to find out.
I know if I reduce the pulse duration to be incredibly short (higher power per individual pulse but less time powered on), the effect goes away or at least reduces substantially, same with if I reduce the power itself but in different ways/amounts
When I look at 1000x magnification it’s still nowhere near close enough to see the actual gratings, but I can see the individual parallel lines that carry the gratings
I’ve seen some SEM images another laser operator took of a similar configuration minus the extra manipulation that I’m doing to the source image prior to lasering https://github.com/benkrasnow/MOPA_Laser_Diffraction_Gratings
I think where mine would differ is there would be less uniformity since I’m changing the laser speed according to the supplied gradient input and this operator was operating at a constant speed, by varying the laser speed the pitch of the pattern is changing as it gets closer to the edge of a shape (or the artwork in its entirety, depending on the scope I use when applying the gradient)
But I would love to see some of these engravings under better magnification, I hadn’t even thought of approaching a university or nearby professional just to run it by them
Do you think someone would really be willing to analyze it for / with me?
11
u/[deleted] 6d ago
[removed] — view removed comment