Would Glass protect against IR?

[Tw15t3r]

I've heard and read around here and there that glass blocks quite a bit of IR. Like mythbusters walking pass an IR detector with a sheet of glass allowed them to pass without triggering the alarm.

So my question is that for all those here who are bespectacled, would we be safe from IR from green lasers especially? (assuming your spectacle lenses are glass and not plastic)

 

[Grix]

Aren't the IR optics made from glass?

 

[Tw15t3r]

I dunno... Most of us use Aixiz modules which use acrylic lenses isn't it?

 

[Things]

Glass will not block regular IR we all experience, glass only starts becoming opaque to IR at >9000nm or so.

 

[Tw15t3r]

Oh... wow that means those motion detectors must be using far infrared region.
And that also means that I gotta be very careful with my green laser since there's gonna be more than just green light hitting me.

Is the diffraction from the IR much larger than the green that I should be worried about getting hit by IR when near the green dot?

 

[ndrew2505]

just dont shine it at anyones face and youll be ok. most times the ir leakage is negligible unless its a super awful quality laser.

 

[Things]

Oh... wow that means those motion detectors must be using far infrared region.
And that also means that I gotta be very careful with my green laser since there's gonna be more than just green light hitting me.

Is the diffraction from the IR much larger than the green that I should be worried about getting hit by IR when near the green dot?

Nope, the only way you should be worried about IR is if you are pointing the laser at your face, but in that case I would be more worried about the visible light ...

 

[Benm]

Glass only blocks far-IR indeed.... like found in CO2 lasers. With a powerful one you can melt holes through glass, or engrave it if you time the exposure right.

 

[HIMNL9]

Careful, that also not all the glasses blocks IR, also far IR ..... any organic based ones, yes ..... CR resins for optics, too ..... acrylate, not too much ..... also pure optic crystal don't block them too much .....

Anyway, you're speaking about near IR, 808nm, so no, glass don't block them, at least if isn't treated specifically for do it, or if is not green or blue colored (but also in these cases, is better to check, cause not all the colorants used in glass making blocks ALL the wavelenghts out of the visible spectrum).

To be sure, about IR blocking (and also about IR emitted from green DPSS modules), if you have a webcam, a b/w camera, or also just an old digital camera, they see IR as pink/white (or white, in case of a b/w telecam) so you can see if a particular glass block or not IR ..... and for see the IR that come out from a green, use a IR filter for take away all the visible, then look at the laser out with the camera.

BTW, just cause professional IR filters are absurdly expensive (and after all, you don't need a big one, just one that fit in front of your camera lens), you can get cheap but almost-professional grade IR pass filter, from unexposed diapositive film.

Just ask your photo store to develope for you an UNEXPOSED (this is important, the film MUST be never used, unexposed) DIAPOSITIVE film, specifying to the lab that it's intentional (otherwise, maybe, they just throw it away and say you that the film was wrong) ..... after the developing process, the diapositive film must look totally black and completely opaque to visible light, but if you look through it with IR, usually you see it transparent, or at maximum a little bit dark, like, 5 or 10% less than without it (this depend from brands and developing processes)

I always used diapositive from ilford, agfa and kodak without problems, for IR pass filters, but none can control the developing process ..... i obtained the better results with "provia" films and new developing bath, 98% IR transfer / 99,8% visible blocking, on an optical test machine ..... and if you need it more big than the 35mm size of the common films size, just use a "120" size diapositive film (the ones used in 6x6 photocams)

Only one advice ..... just cause it's completely black, don't use it for look directly at the sun, or inside a DPSS module, or similar, don't even think to do it ..... it block ONLY the visible part, and the IR part can still damage your eye the same !

 

[Tw15t3r]

Wow! Thanks for all the info HIMNL9! The visible light filter sounds like a very good way to test IR leakage. I guess I'll go get it when I get a meter. Then I'll know how much IR leakage I'm getting.

 

[HIMNL9]

Just take care to not focus the beam at the filter, cause photo film is basically plastic based, and as any other black plastic it can melt

Anyway, at that cost for the filter ..... and if you know a photo shop, you can always ask if they can gift you the discarded piece of film that usually come with the dia, when the lab send them back after the develope process ..... i mean, the "queue" part that remain inside the film holder, and that when they develope it, appears all black ..... here, most of those labs always send back also this part, with the prepared diapositives, for show to the client that the roll was totally developed, and usually it become discarded when the client get his diapositives ..... also if is a little piece, for an experiment is good the same

 

[PlasmaCube]

Glass only blocks far-IR indeed.... like found in CO2 lasers. With a powerful one you can melt holes through glass, or engrave it if you time the exposure right.

Just as a side note, technically CO2 lasers emit long-wavelength infrared, or mid infrared, depending on who you ask. Far infrared is usually defined as 15000nm and up, and CO2's operate at around 10600nm.

 

[Laser_Ben]

 

[Slipstream]

How did you answer :
Would Glass protect against IR?

with your post? :evil:

 

[Tw15t3r]

Looks like whatever that thing is that is graphed blocks out visible light, which could be what HIMNL9 said: A developed, unexposed, diapositive film.

 

[HIMNL9]

^ i'm not sure about the UV part, with the dia, cause til now i only used them for IR applications (nightvision survey, fake money detectors, and so on) ..... must try the UV part too, when i have time.

Anyway, that graph say "MIRON-GLAS", i suppose that is some sorta of glass filter, also if i've never heard that name.