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Optical diffraction patterns made with a MOPA laser engraving machine [video]

166 points by emsign 1y ago

hnthrowawayacct 1y ago
This guy always has an unreal amount of engineering lift for hobby videos. A treat to watch every time.
- JKCalhoun 1y ago
  Yeah, a YouTube treasure. For anyone new to his channel, you have a back log of amazing experiments to binge on. I believe he works at Alphabet (tangent?)—somewhere in the Bay Area.
  - quux 1y ago
    IIRC he works (worked) for Verily, and previously was at Valve working on their VR hardware. He's also mentioned having a business pre-Valve that made MRI safe controllers for users to interact with computers while inside an MRI machine.
- ThrowawayTestr 1y ago
  What a 10x engineer does in his free time
- egeres 1y ago
  It's a completely different level, he has my favorite combo, incredibly detailed videos with fresh and complex engineering ideas
  - jayrot 1y ago
    Also, really the holy grail of YouTubers — he’s not concerned with clicks or retention. He has a day job, he’s not trying to do this full time or make a career out of it. I’ve been following him for years. Legitimately just an insanely smart person doing projects on his own time he thinks are interesting and that he thinks other people might be interested in too. It’s kinda crazy when it’s as simple as that with no ulterior motives or incentives.
mikkupikku 1y ago
Pity it won't work for chocolate holograms.
- alganet 1y ago
  Why not?
  - ThrowawayTestr 1y ago
    Because chocolate doesn't form oxides
    - ggm-at-algebras 1y ago
      You need a mechanism which forms interference fringes. Chocolate blooms, so you might be able to etch the bloom. Otherwise, it's skim an edible oxide layer over the chocolate to etch.
    - alganet 1y ago
      I thought the oxides were just for color variation. Maybe I misunderstood that part.
  - rainbowzootsuit 1y ago
    Colors are from oxide layers and dont create a geometric structure that can be molded. He explains in the video.
    - ginko 1y ago
      I wonder if you could etch the oxide layer away to leave the metal pits.
      - kragen 1y ago
        Maybe, but stainless may not be the best material for that, because the oxide layer formed is largely chromia, and chromia is a motherfucker, which is why stainless doesn't rust. Etching chromium off the chromia sounds practically difficult but probably feasible; etching chromia while leaving metals sounds hard. Maybe molten sodium hydroxide? Instead, you could choose a different metal whose oxides are easy to etch. Magnesium is probably the extreme case here, with an oxide that instantly vanishes in the weakest of acids, but if someone gave me a US$7000 fiber laser, I would try to keep the laser beam away from thin pieces of magnesium. But mild steel, for example, forms oxides that etch pretty easily with acids. I think copper oxides also etch easily with either acids or bases, too, and the copper itself is more resistant to etching. Really, though, if you're molding silicone or chocolate, you don't need the high strength, flexibility, conductivity, etc., of metals. Maybe etch your grating into a material chosen for other properties. Glass, for example, is perfectly isotropic and has no grain structure to introduce into your cuts, and it has a low TCE. It sticks to silicone, but not to chocolate. Fused quartz is a glass with a near-zero TCE. I assume but don't know that the MOPA laser can ablate the glass surface. Other amorphous solids might be more amenable to easy laser shaping and not stick to silicone. Sugar glass, for example.
brcmthrowaway 1y ago
Could this be used to make a diffraction grating on PMMA?
- tecleandor 1y ago
  I don't think so, but corrections are welcome. It's also mentioned in another comment and (I think) the video about how it wouldn't work in chocolate. As it works creating oxide layers, not a diffraction structure: If you try it directly on PMMA it won't create a diffraction structure, but a kinda slightly melted surface. I don't know if etching would be possible with enough precision on PMMA. If you do it on steel and use it as a mold to pour (?) PMMA, as people do with chocolate and diffraction grates on plastic, there's no structure to transfer.
mjb 1y ago
That's much better results than mine! I notice a similar 'holographic' effect when coloring titanium a couple weeks back, and experimented with getting them dialed in along the same lines as this video. I didn't have nearly as much success, despite the underlying physics being similar. My guess is that the much lower thermal conductivity of titanium causes a lot more smudging than on stainless, which makes the grating effect less pronounced. One interesting thing I noted with Ti is that satin finished Ti (media blasted with 500 grit glass media) won't take a color from electrocoloring, but will from MOPA laser coloring. Not nearly as nice as polished Ti, but still there. Given that they are such similar processes (growing a set thickness oxide layer), its somewhat surprising to see different results. I guess I'm going to have to experiment on some polished 304.
- kragen 1y ago
  Maybe you're melting the metal surface flat before the oxide forms on top of it?
kelseyfrog 1y ago
I'm confused by the authors description of holograms and my own understanding. He starts to go down a path of holographic "pixels," but whai I know about holograms is that the holographic image doesn't have such a concept - the image is delocalized. There have been some successful attempts at handmade holograms[1] that I wonder how the video creator could adapt. 1. http://amasci.com/amateur/holo1.html http://amasci.com/amateur/holo1.html
- somat 1y ago
  I suspect that the idea is that the simple way to etch a hologram in the surface is to have a set of holographic picture elements(pixels) where each element hologram would get etched for each pixel in the source image. It also sounds like this was a minor side experiment and found not to work as expected so not much further effort was put into it.
- rcxdude 1y ago
  I think he's thinking like lenticular images which are often described as 'holograms', since the apparent color changes with the viewing angle like with the lenticular images.
neilv 1y ago
YouTube wouldn't show me this video using Firefox, even with uBlock Origin disabled: > Sign in to confirm you’re not a bot > This helps protect our community. Learn more > Sign in But it would show me the video using Chromium, without an account configured.
- bayindirh 1y ago
  Probably it authenticates your browser via the Chrome validation header [0]. Remote attestation, anyone? [0]: https://github.com/dsekz/chrome-x-browser-validation-header https://github.com/dsekz/chrome-x-browser-validation-header

166 points by emsign 1y ago

hnthrowawayacct 1y ago

This guy always has an unreal amount of engineering lift for hobby videos. A treat to watch every time.

JKCalhoun 1y ago
Yeah, a YouTube treasure. For anyone new to his channel, you have a back log of amazing experiments to binge on. I believe he works at Alphabet (tangent?)—somewhere in the Bay Area.
- quux 1y ago
  IIRC he works (worked) for Verily, and previously was at Valve working on their VR hardware. He's also mentioned having a business pre-Valve that made MRI safe controllers for users to interact with computers while inside an MRI machine.
ThrowawayTestr 1y ago
What a 10x engineer does in his free time
egeres 1y ago
It's a completely different level, he has my favorite combo, incredibly detailed videos with fresh and complex engineering ideas
- jayrot 1y ago
  Also, really the holy grail of YouTubers — he’s not concerned with clicks or retention. He has a day job, he’s not trying to do this full time or make a career out of it. I’ve been following him for years. Legitimately just an insanely smart person doing projects on his own time he thinks are interesting and that he thinks other people might be interested in too. It’s kinda crazy when it’s as simple as that with no ulterior motives or incentives.

mikkupikku 1y ago

Pity it won't work for chocolate holograms.

alganet 1y ago
Why not?
- ThrowawayTestr 1y ago
  Because chocolate doesn't form oxides
  - ggm-at-algebras 1y ago
    You need a mechanism which forms interference fringes. Chocolate blooms, so you might be able to etch the bloom. Otherwise, it's skim an edible oxide layer over the chocolate to etch.
  - alganet 1y ago
    I thought the oxides were just for color variation. Maybe I misunderstood that part.
- rainbowzootsuit 1y ago
  Colors are from oxide layers and dont create a geometric structure that can be molded. He explains in the video.
  - ginko 1y ago
    I wonder if you could etch the oxide layer away to leave the metal pits.
    - kragen 1y ago
      Maybe, but stainless may not be the best material for that, because the oxide layer formed is largely chromia, and chromia is a motherfucker, which is why stainless doesn't rust. Etching chromium off the chromia sounds practically difficult but probably feasible; etching chromia while leaving metals sounds hard. Maybe molten sodium hydroxide? Instead, you could choose a different metal whose oxides are easy to etch. Magnesium is probably the extreme case here, with an oxide that instantly vanishes in the weakest of acids, but if someone gave me a US$7000 fiber laser, I would try to keep the laser beam away from thin pieces of magnesium. But mild steel, for example, forms oxides that etch pretty easily with acids. I think copper oxides also etch easily with either acids or bases, too, and the copper itself is more resistant to etching. Really, though, if you're molding silicone or chocolate, you don't need the high strength, flexibility, conductivity, etc., of metals. Maybe etch your grating into a material chosen for other properties. Glass, for example, is perfectly isotropic and has no grain structure to introduce into your cuts, and it has a low TCE. It sticks to silicone, but not to chocolate. Fused quartz is a glass with a near-zero TCE. I assume but don't know that the MOPA laser can ablate the glass surface. Other amorphous solids might be more amenable to easy laser shaping and not stick to silicone. Sugar glass, for example.

brcmthrowaway 1y ago

Could this be used to make a diffraction grating on PMMA?

tecleandor 1y ago
I don't think so, but corrections are welcome. It's also mentioned in another comment and (I think) the video about how it wouldn't work in chocolate. As it works creating oxide layers, not a diffraction structure: If you try it directly on PMMA it won't create a diffraction structure, but a kinda slightly melted surface. I don't know if etching would be possible with enough precision on PMMA. If you do it on steel and use it as a mold to pour (?) PMMA, as people do with chocolate and diffraction grates on plastic, there's no structure to transfer.

mjb 1y ago

That's much better results than mine! I notice a similar 'holographic' effect when coloring titanium a couple weeks back, and experimented with getting them dialed in along the same lines as this video. I didn't have nearly as much success, despite the underlying physics being similar. My guess is that the much lower thermal conductivity of titanium causes a lot more smudging than on stainless, which makes the grating effect less pronounced. One interesting thing I noted with Ti is that satin finished Ti (media blasted with 500 grit glass media) won't take a color from electrocoloring, but will from MOPA laser coloring. Not nearly as nice as polished Ti, but still there. Given that they are such similar processes (growing a set thickness oxide layer), its somewhat surprising to see different results. I guess I'm going to have to experiment on some polished 304.

kragen 1y ago
Maybe you're melting the metal surface flat before the oxide forms on top of it?

kelseyfrog 1y ago

I'm confused by the authors description of holograms and my own understanding. He starts to go down a path of holographic "pixels," but whai I know about holograms is that the holographic image doesn't have such a concept - the image is delocalized. There have been some successful attempts at handmade holograms[1] that I wonder how the video creator could adapt. 1. http://amasci.com/amateur/holo1.html http://amasci.com/amateur/holo1.html

somat 1y ago
I suspect that the idea is that the simple way to etch a hologram in the surface is to have a set of holographic picture elements(pixels) where each element hologram would get etched for each pixel in the source image. It also sounds like this was a minor side experiment and found not to work as expected so not much further effort was put into it.
rcxdude 1y ago
I think he's thinking like lenticular images which are often described as 'holograms', since the apparent color changes with the viewing angle like with the lenticular images.

neilv 1y ago

YouTube wouldn't show me this video using Firefox, even with uBlock Origin disabled: > Sign in to confirm you’re not a bot > This helps protect our community. Learn more > Sign in But it would show me the video using Chromium, without an account configured.

bayindirh 1y ago
Probably it authenticates your browser via the Chrome validation header [0]. Remote attestation, anyone? [0]: https://github.com/dsekz/chrome-x-browser-validation-header https://github.com/dsekz/chrome-x-browser-validation-header