Goggles for CO2 Laser?

So I finished a modest CO2 laser build, nothing special, and of course I bought goggles for it, and I always wear them and everyone always says to and I definitely have seen the horror stories from the 445s and other visible light lasers and such but I just have to ask: why are they needed for CO2 lasers?

I could be completely wrong in my logic, but I just kinda figured that far IR light wasn't able to blind you because it doesn't focus on your retina, as of course is why you can't see it. Is the only danger solely from actually scorching your eye with the laser? I just wanted to know if the small reflections are actually dangerous? Or is it just for accidental "somehow I managed to stare into the beam without first burning other body parts"? I will of course always wear the appropriate goggles for whatever laser I'm using, but I was just super curious.

Thanks guys!

You are correct in that the outer layers of your eye will absorb the far IR light, however CO2 lasers being the high power they are, you need to be really careful of reflections. The wavelength will reflect off anything even remotely shiny. When I was aligning my laser cutter, the laser was constantly hitting the dull aluminium parts and reflecting off. Once I even walked past and felt warmth on my face! (With goggles on of course). Better safe than sorry.

Light in the 9-11 micron wavelength range, including 10.6 microns produced by a CO2 laser, is very efficiently absorbed by water. Since your eye is mostly water, this means the light is absorbed at the surface of your eye. The damage threshold for CO2 beams is drastically higher, since you do not get the increase in irradiance that happens with visible light focusing onto the retina. This is an impressive difference since a 1mm diameter visible beam on the surface of your eye can focus to a few microns on your retina (1,000,000 times the irradiance).

You are still subject to injury if a beam hits you directly in the eye. For starters, the laser is a lot more powerful than your typical visible laser. You can't see the light at all, so you get no visual cue to look away. The damage will be different: rather than losing vision in a particular location for a visible/near-IR beam, your vision will be degraded over a wide region (more like a cataract).

Since the required glasses are totally clear and very cheap, there is absolutely no reason to not wear them.

The transition of your eye from clear to opaque is somewhere in the 1.2-1.4 micron range. 1.5 microns is considered "eye safe" for military applications.

Ah ok thanks guys, it was never a question of not wearing them I just wanted to be better informed. Good info to know.

and yeah I had similar experiences aligning my laser, thought everything was aligned perfectly when I suddenly noticed smoke rising from my shoe Those pesky invisible wavelengths