Laser Safety Glasses Question

Databyter

Enlightened
Joined
Oct 12, 2005
Messages
525
Location
San Diego
I've browsed a few laser safety glasses sites and have come up with a few more questions than answers. So what better place to come than CPF!

Question number one.

Should I worry about filtering the ir frequencies (808 and 1064 I believe) if I am not going to do any pointer surgury or modification or just get the straight 532 nm and save some money. Mostly I would be pointing in the sky with no glasses needed (astronomy outings) but every once in a while I like to take it out and see the beam in the privacy of my home and marvel at it and check the batteries (my excuse).
I notice the glasses that have all three coatings are not as clear and more expensive so if there is no chance of ir leakage I wouldn't think I would need the extra two coatings..right?

Question number two.

The coatings seem to vary in intensity and have number values as to how much of that wavelength they block. This makes sense because lets face it if they all blocked out 100% of the wavelength you wouldn't see a darn thing. So whats a good tradeoff between seeing your beam in the air and being protected from a reflection. How many layers or what value of occlusion?

Question number three.

Any specific recommendations on a comfortable affordable set of laser safety glasses that incorporate the answers to questions one and two?


Thanks in advance.
 
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nero_design

Enlightened
Joined
Sep 30, 2004
Messages
211
Location
Sydney, Australia
Q #1: I wouldn't worry about filtering frequencies. Much of the IR light is reduced before it exits the resonance crystal. It is my understanding that the only time the visible beam carrying an invisible IR lightwave can properly split is when the laser is fired into a refractive lens of some sort (could be a glass sphere, a prism etc). Otherwise, the two beams are pretty much piggybacked. Of course, never remove the IR filter on your laser... that's always a very bad idea. I understand the desire to "check the beam" and in a sense experiment with the laser at home so depending on the power of your laser, it may be worth investing in a pair of safety glasses if you do anything which might result in an accidental reflection from something (eg. window, mirror, picture frame, watch, glasses, jewellery, television screen, camera, glass shelves, chrome doorknob etc.) Even shiny plastic and glossy printing paper will give you a specular reflection. You make the decision based on the risk and also the power of your laser. Most starpointing lasers are under 30mW and are really only likely to be harmful with a direct application to the eye... or a reflection from a mirror. Anything beyond the 40mW range is outputting very serious power levels and so it is well worth buying glasses to protect your eyes unless you only use it for astronomy.

Q #2: I think you will find about three different grades of laser safety glasses. There might even be more. Indeed, the triple coated models block much of the visible laser light spectrum. Most sold for hobbyists seem to allow enough light to pass through to allow the dot and sometimes even the beam to show. I believe that the primary purpose of the laser safety glasses is to assist in protecting against specular reflections (from a reflective surface). I note that the beam itself, though diminished, will pass through most laser safety glasses if directly aimed through them although the power and heat spot is reduced. So their purpose is more to protect against direct reflections from Class IIIB lasers. Class IIIA lasers are not likely to offer harmful reflections and Class IV lasers are much more powerful & require much more caution in their operation and handling.

Q #3: There's quite a few suppliers online. I have purchased 532nm protective glasses (for green laser wavelengths) from Wicked Lasers myself since they offered a deal at the time with both laser purchase and protective glasses....although you will also occasionally find them on E-Bay and even from numerous laser module suppliers. The ones I have do work and they do so effectively for split beams and reflections of lasers just over the 100mW strengths without trouble. They range from $79 up to several hundred dollars depending on the supplier. Be sure to get glasses rated for the specific wavelength of laser you are using. Experiments like burning plastic and igniting match heads etc demand the use of glasses but in all seriousness, any indoor use of a laser over 30mW has the potential for hazard if the laser light accidentally reflects off another surface. Sure, a laser over 5mW is a Class IIIB and therefore potentially more hazardous than a Class IIIA Pointer but I feel that the potential for self harm is greater for models over the 35mW range (just from my own mishaps). Still, you don't ever want to point one at yourself, even with safety glasses on. For astronomical use of a laser as a starpointer, protective glasses are useless of course and generally entirely unnecessary. But for indoor applications including photography and optical experiments, especially with lasers of higher power, it's essential to protect your eyes from reflections. In such cases, the visible light wavelength is going to be much more of a hazard to you than stray IR light. I note that safety glasses come in several different designs: goggles and sunglasses style with individual or dual lenses. They all seem to have a cherry-red colour in order to properly filter the desired wavelength. Do not confuse "laser enhancer goggles" with "laser safety goggles", even if you find them both on the safety pages of a supplier's website. The enhancers will not protect your eyes at all but will make the beam and dot slightly more visible to the eye.
 
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