I'm building a laser cutter/engraver using a 40W CO2 laser, and I want to provide a window in the case so I can monitor things when the laser is on.

I have various sheets of transparent plastic, but of course I want to make sure that any stray laser energy doesn't pass through the window and blind me.

I know that the wavelength of the laser output is 10600 nm (invisible infra-red), but I don't know how to determine whether a given candidate material is opaque enough to be acceptable.

I've looked for this information online (assuming that it would be in the specifications provided by the manufacturer), and I've run into two problems with that approach:

  • This information is rarely in the specs I've been able to find
  • In many cases I have scrap/donated material of unknown origin, so rather than rely on specs for what I THINK the material is, I'd much rather TEST.

Can anyone recommend a method of assuring that a given piece of test polycarb, Plexiglas, etc. is opaque at 10,600 nm?

NOTE: Any stray laser energy that bounces up from the bed would be far too diffuse to melt this material. However, it might be strong enough to damage a retina if it passed through undiminished.

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    $\begingroup$ Use a plastic certified for the application. Pretty straightforward for a CO2 laser. Do not roll your own. $\endgroup$ – Jon Custer May 23 '17 at 0:14
  • $\begingroup$ @JonCuster - I assume I'd have to buy a sheet of certified material. OK, what certification and where to look? $\endgroup$ – Scott Smith May 23 '17 at 0:30
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    $\begingroup$ Google for laser supply houses. Pick one. Call and discuss your application. But what they suggest. $\endgroup$ – Jon Custer May 23 '17 at 1:07
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    $\begingroup$ You're building your own 40W CO2 laser cutting system - a Class-4 laser with an invisible beam to boot - and you're having to go online to strangers in order to solicit advice on how design a safe system? This has "bad news" written all over it. $\endgroup$ – user93237 May 23 '17 at 5:05

I want to make this an answer rather than a comment so search finds it.

Don't mess around with high-power invisible lasers if you don't know what you are doing (in fact try and avoid high power invisible laser even if you do!). If you can't work out what OD you need to block 40W of invisible laser power when a couple of 0.001 W can blind you - then you probably shouldn't be asking on the internet.

Instead make an opaque metal cover and a safety switch that kills the laser if it's opened - and put a small cheap $10 webcam inside to monitor it.

However my professional advice is don't - don't do any of this, 40W of invisible IR laser is dangerous and you really don't want to play with this at home.

ps. You also want to worry about the exhaust system and getting rid of the interesting chemicals given off by burning plastics.

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    $\begingroup$ "However my professional advice is don't - don't do any of this, 40W of invisible IR laser is dangerous and you really don't want to play with this at home." - Absolutely agree. $\endgroup$ – user93237 May 23 '17 at 5:06

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