Safety with 50mW 532 nm laser pointer

[GellMann]

Hi all,

I hope it's okay that I'm posting this thread. I'm (hopefully) not just a newbie that hasn't read a thing here and posts an obnoxious and redundant thread - I purchased my first couple laser pointers a couple weeks ago after combing these forums for a couple days to figure out how and what to buy. The first one, described in the title, arrived yesterday, along with a small optics kit, from optotronics. On the sheet that came with it, it says the measured power output is 57mW, so I believe that they tested it because that store was highly recommended here and elsewhere. I ordered the relevant safetly goggles from the Survival Laser Store, and they work like a charm - you can only see the dot through them, and it's quite dim and an orange-ish color.

My first attempt to use the laser was to recreate the double-slit experiment, because I'm a physics grad student and physics is cool, but the laser beam is so small that I'm having trouble creating "slits" small enough and close enough together. But that's not what this thread is about - it's really freakin hard to do this because I have carefully read here and other sources to make sure I don't screw up my vision, and I know it would obviously be horrible to catch a reflected beam or the original beam directly in the eyes, but I also get the impression that it's dangerous to even look at the dot without protection. I know I can look at the beam itself from the side without issue, but I'm working indoors and so most cases looking at the beam would also make me see more of the dot than I'd want to. But I also haven't seen it explicitly, definitively stated that you can't look at the dot if it's in the same room as you. But I've been working under the impression that I shouldn't, which means it's virtually impossible to properly aim the pointer towards a slit, and then check whether or not I can get the diffraction pattern, and so I sit here wondering why I bought this particular laser in the first place!

So my question is, is it a guarantee that, even if I have cleared the area of all reflective objects and know I won't get struck in the eye with the beam, I need to have my goggles on at all times? Because the dot itself is dangerous for my sight? (I wouldn't STARE at it even if I had the goggles off to try and aim the beam properly, just couldn't guarantee NOT looing at it briefly ya know). If so, I'll need to purchase some sort of lab-like setup that lets me do this stuff incredibly precisely, I guess.

For reference, I'm maybe 12-15 feet from the wall I'm shining towards, and do work on a table with beam splitters/reflectors as well.

Also, for laser pointer pens with a push-in button that doesn't stay on, does anyone know of any items that are handy for keeping it still and stable?

Thanks all.

 

[smallfreak]

You are not likely to hurt your eyes, by looking at a diffuse reflection of a 50mW Laser, even at relatively small distances. The power dissipates with the square of the distance —as you certainly know.

You should avoid using magnifiers to watch the dot, as you would again gather much more of the diverging light.

If you use a black target, you can eliminate much of the power and it would never be wrong to use your goggles, as long as you are able to see the spot.

Doing a double slit experiment with visible wavelength requires very tight spacing. You can broaden the beam with a beam expander, but that still requires the spacing to be less than a couple of micrometers to get a good interference. As you know, the fan-angle is a function of the spacing in relation to the wavelength.

You could try to define a gap with two razor blades in about tripple „hair thickness“ and mount a hair smack in the middle which will give you two windows in a suitable distance. And you might have to mask off the center dot at the target to see the faint diffraction pattern from just two slits as compared to a full grating.

 

[Immo1282]

As smallfreak said - "diffuse" or matte reflections of the dot aren't going to do any harm - it may be uncomfortable to look w/o goggles - but it's not going to hurt you unless you get a direct hit/specular (or mirror) reflection. So make sure there's no mirrors/glass/polished metal around where you're working and you should be safe.

Another way to ensure goggle-free safety is to bolt your laser down to a bench - Most accidents happen to experienced people when people lose control of their lasers (drop them, roll off a table etc). By securing it down to a stable work surface - you'll reduce risk further.

If you're enjoying doing a couple of experiments etc. by all means please post an introduction with your rough location (country/state is all that's needed) if you plan to stick around

 

[GellMann]

Thanks for the replies! smallfreak - yeah, the next laser I have coming in should be thick enough in diameter to work with the slit setup I was able to get last night, which I could get to work briefly with the 532nm, though not stable enough to get a picture. I need to figure out what pieces to order to stabilize my laser and setup, like Immo1292 suggests.

And I can do that, Immo1282! I have to get to campus right now but sometime when I'm back on the forum I can write that up.