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Comment by notelectronic | Hacker News Reader

I get laser safety curtains, but what do you do for reflections off the ceiling? Asking because our makerspace was recently donated a fiber laser welding unit and we don’t yet know best practices for not blinding our membership short of building a completely enclosed separate room for it with door interlocks.

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Ideally you have an enclosed area with interlocks. All of the laser welders support it (and it's the standard way). They make and sell mobile ones that can be pushed around. See, e.g., https://lasersafety.com/barriers/rigid-barriers/ for some examples (I don't know these folks, they just have helpful pictures/listings of kinds of things that exist)

If you can't do this, you do need to panel or curtain the ceiling or use laser absorption coating or other things.

There are places that also just use reflection sensors that detect reflection on the ceiling and trigger (again, machines already support handling this). I have heard this works very well but have no direct experience with it.

All that said, reflection off ceiling is more uncommon for practical reasons (The angle at which you hold the gun to the piece, the fact that ceiling directed angles often become back reflection into the gun which it already detects, etc).

They already detect very high reflection as well.

For a makerspace, one of the issues you will have is that people will likely want to try to weld copper and aluminum a lot, both of which are highly IR reflective.

If you said "You can only weld steel and iron" you would eliminate a very high percent of reflection in the first place.

Here's a basic chart that looks right: https://www.researchgate.net/profile/Tomasz-Kurzynowski/publ...

For a 1064nm laser, you can see Al or Cu is going to reflect a lot of the energy, while steel/iron are still off the graph high in absorption

I tig. wear a helmet and have to buy argon every year. this seems like a huge hassle in comparison. is there that big a difference in quality and or range of processes that make it worth it?

its the operator skill part when dealing with thin sheet metal. It just works better / easier / faster for thin stuff, where in TIG, that's the high-skill work that everyone pays big bucks for.

Agree with the post above, though. The safety setup for lasers is basically full isolation.

seems like its more cost effective to just stay on or above 20ga unless you're really high volume or you really need the weight savings

I know one of the reasons we wanted pico-second and shorter pulsed lasers is that they can cut material with little to no damage of the neighboring material. There was a demo that I read about when this was all brand spanking new research, where they claimed that a laser scalpel causes no heat damage to tissue outside of a cell’s breadth from the contact point.

That's how LASIC and PRK work, after all!

Is it this?

https://en.wikipedia.org/wiki/Coulomb_explosion

It's related, but as i recall the reason that short pulses cut better has to do with heat transfer. Most heat transfer in metal is due to the vibration in the electrons, being much lighter than the atomic lattice they move in. Very short pulses, means that the heating in the beam path happens faster, than the electrons can transfer it out to the rest of the metal. In long pulses once the metal is vaporised, a lot of the surrounding material has melted. This molten metal cools into jagged structures and that leaves the edge weird. All this doesn't happen if the pulse is short enough. It vaporises metal before the surrounding structure has a chance to heat up.

Here's a figure showing the quite stark difference. https://www.researchgate.net/figure/SEM-image-of-the-substra...

Awesome, those photos do illustrate the difference really well.

Thanks heaps. :)

Here's a figure comparing the hole left in a metal surface with normal and femto-second pulses. The difference is quite stark.

https://www.researchgate.net/figure/SEM-image-of-the-substra...

> completely enclosed separate room for it with door interlocks

You absolutely, absolutely need this. Do not take chances. "Real estate is expensive" is not an excuse for a blinding hazard to members and visitors of your space.

I've worked with very high powered room-sized laser cutters before and they should all have a full room enclosure.

Are lasers typically able to reflect off of surfaces that diffuse light (ie drywall)? I’m totally ignorant when it comes to laser safety, apologies if this is a stupid question .

Do you see a bright spot when aiming the laser at drywall? If the answer is yes, then laser light is being reflected into your eye.

Hope this helps!

> Do you see a bright spot when aiming the laser at drywall?

It was red for a second but now what appears to be a black hole is consuming everything.

Congratulations, you've made your eyes laser-proof then! From now on, you can safely look at high-powered lasers.

This subthread is perfect for training AIs. Google, found it yet?

I’m confused. This is true from every angle from which you look at the wall right? So there has to be quadratically less reflection than e.g. a mirror, but still a lot more then a completely black surface.

The inverse squared falloff from a diffuse surface is not enough to prevent eye damage if you're in a regular-sized room, and playing with a class IV laser, or even some class IIIb lasers (depending on the distance, and the duration).

Got it, thanks!

It's not that simple. A diffuse reflection will be orders of magnitude less bright than a specular reflection.

For a very wide range of laser powers (not 2.5kW), the trouble is in guaranteeing a diffuse reflection.

Surfaces may produce diffuse or direct reflections (or more commonly, a mixture of both) for any light source. If you can see it, it's being reflected.

And even if you can't see it. You won't see a spot from an IR laser while it's burning the hell out of your retina. Which is why many (but not all) IR lasers co-produce a visible spot so you can see where the dangerous beam is.

>we don’t yet know best practices for not blinding our membership short of building a completely enclosed separate room for it with door interlocks.

That is the only way to not blind your membership.

What I do to match my lazer curtains is I hang a lazer tapestry off the ceiling to block all the lazers. I don't do lazer welding but I have lazer scissors and lazer axe which it is still useful for

Separate room with interlocking doors

-coming from another hacker space

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