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Quick and dirty test for IR emissions from a green laser?

O

OpenTrackRacer

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I've read the NIST paper but it occurred to me to try a different test. I'd like to hear feedback on the validity of this.

My cellphone front camera is very sensitive to IR. A remote control looks like a flashlight. So, I took my green laser and put it against HDE red 405-532nm glasses (which should block all the visible green light). Looking at the glasses (obliquely of course) I can see a dim red dot. The camera pretty much sees the same thing. This leads me to believe that my green laser has an IR filter.

Comments and critiques?

Thanks!
 
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Sounds like fluorescence from the lens of the glasses to me.
 
I agree, fluorescence, I've seen it before.

If you had a filter which passes IR but blocks visible spectrum light, you could shoot the beam through that and either measure the IR with a laser power meter, or use a camera sensitive to that wavelength to see if IR is present. Using such a filter I tested some cheap 532nm laser pointers without IR filters built into them and found about 20-30% of the power they produced to be in the IR spectrum. If you are using a LPM with those cheap 8 dollar China ebay pointers and measure a total of 50mw output, you are probably getting closer to 35-40 mw of green, the rest IR.
 
I did a test with a cheap M301 532 green and my LPM. with out the filter it read 130mw, with the filter it read 80mw! I don't use those cheap HDE glasses for any thing other than testing DPSS greens for IR.
Ed
 
Yeah, I'm not confident in the HDE glasses at all. Got a pair with a cheap 450nm laser I bought off eBay to play with. Getting better glasses delivered today. As for the test, yes the dot visible through the HDE glasses is likely fluorescence (which is not surprising). However, it's just as dim in the camera as it is with the naked eye and there is no halo or other stray light. The HDE glasses do not block IR. That leads me to believe that the laser isn't putting out any IR. If I put a remote control on the other side of the glasses the IR is clearly evident.

It seems like a valid test to me but...
 
OpenTrackRacer said:
Yeah, I'm not confident in the HDE glasses at all. Got a pair with a cheap 450nm laser I bought off eBay to play with. Getting better glasses delivered today. As for the test, yes the dot visible through the HDE glasses is likely fluorescence (which is not surprising). However, it's just as dim in the camera as it is with the naked eye and there is no halo or other stray light. The HDE glasses do not block IR. That leads me to believe that the laser isn't putting out any IR. If I put a remote control on the other side of the glasses the IR is clearly evident.

It seems like a valid test to me but...
Click to expand...


Oh, we're talking about the 450nm laser? I just assumed we were talking about a 532nm laser.

450nm lasers don't require IR filters as they don't emit IR. The only common one you'll fine that does is 532nm, and that's because they are DPSS (Diode Pumped Solid State) rather than direct diode, like 405,450,520,635,650,660.

Diagram of a 532nm DPSS laser pointer:

glpmca1.gif


If you have any questions regarding this feel free to ask.
 
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No, sorry. The glasses came with a 450nm laser but I was using them to test a 532nm laser I've had for years.
 
OpenTrackRacer said:
No, sorry. The glasses came with a 450nm laser but I was using them to test a 532nm laser I've had for years.
Click to expand...


Ahh I see, fair enough.

Sounds like there's no/very little IR.

It's also possible that your camera just can't detect the IR from the laser (808, 1064) but it can see the remote.

Best way to test is with an LPM and IR filter (either block or pass would be suitable).
 
Agreed. Remote controls should be around 870nm or 930–950nm so it's possible. The NIST study was pretty confident of consumer cameras being able to detect IR emissions from unfiltered green lasers at 808nm and 1064nm but it's still a quick and dirty test. I have an old Russian night vision scope that I could take a peek with too. I tried with my thermal camera and it doesn't see the emissions from a remote (too high a frequency for it I expect).

I do have laser glasses that block IR specifically so I can play with those too and see if they make a difference in what the camera sees.

Probably beating a dead horse at this point but it's interesting so what the heck!
 
What do you know. It turns out that I have access to a Coherent LaserCheck and a ThorLabs LPM so I guess I'll play around with those and see what results I get. Much better!
 
Thought remotes were closer to 750nm?

CCDs don't see 1064nm well at all, they aren't very sensitive at that wavelength.

OpenTrackRacer said:
What do you know. It turns out that I have access to a Coherent LaserCheck and a ThorLabs LPM so I guess I'll play around with those and see what results I get. Much better!
Click to expand...

I assume the ThorLabs LPM is thermal? Best use that if it is. LaserChecks are good, but they are optical and must have the wavelength set right, which is not possible to do if you have more than one wavelength.
 
Well, the LaserCheck has a dead battery and they're not user replaceable so that's probably out. Might see if I can crack it and replace the battery myself. Otherwise it's non-serviceable. The ThorLabs has a couple sensors with it. One is photodiode 400-1100nm but 50mW max. The other is fiber coupled and good to 1W but testing with a laser pointer would be difficult. Researching...
 
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