Infrared lasers?

[GooeyGus]

The 1064 made by the laser is collimated sure, but the amount you're actually getting out in that collimated beam is less than 5mW, even on a hugely powerful laser.

This is due to the way a laser cavity works. If all the 1064nm light was making it out, the laser wouldn't lase at all. Almost 100% of that 1064nm light needs to stay in the lasing cavity in order to build enough gain to lase. The coatings on the crystal, or the output coupler, are coated to reflect 99.9% of the 1064nm light back to the source. Therefore you get some 1064nm leakage, but nothing of any power worth mentioning. It's like the HR mirror on an argon laser... coated for 99.9% reflection, even at 5+ watts of output power the leakage out of the HR is only a few mW.

 

[GooeyGus]

GooeyGus, you have done a nice job summarizing what everyone on LPF "knows." I believed it too, until I actually ran some tests. It's clear that you have never done this.

The amazing thing is how very easy it is to run the tests, but apparently nobody bothers because they all "know the TRUTH!"

I find this absolutely fascinating. Its similar to how, not so long ago, everyone knew that the world was flat, despite evidence to the contrary.

The fact is, I don't particularly worry about IR, but I like to know what the hazards are. "What you don't know can blind you."

I've done "the tests".

The bottom line is the green is much bigger deal than the IR.

The stigma around here is ridiculous. Pretty soon people will be running around with 50mW green lasers wearing 808/1064 goggles because they think IR is so dangerous, meanwhile they're blinding themselves with the green.

 

[Warske]

The 1064 made by the laser is collimated sure, but the amount you're actually getting out in that collimated beam is less than 5mW, even on a hugely powerful laser.

Interesting notion. I measured the output power as being 22% 1064 nm IR.

I noticed o-like is quoting between 20% and 27% IR on one of their green lasers that has no IR filter:

...it is around 250-300mW green and 50-80mW IR .

Sincerely
Susie

I'm surprised they would be quoting such a high percentage of IR if it were really much smaller. Maybe they don't know what they are doing either.

This is due to the way a laser cavity works. If all the 1064nm light was making it out, the laser wouldn't lase at all. Almost 100% of that 1064nm light needs to stay in the lasing cavity in order to build enough gain to lase. The coatings on the crystal, or the output coupler, are coated to reflect 99.9% of the 1064nm light back to the source. Therefore you get some 1064nm leakage, but nothing of any power worth mentioning.

By your logic, you get essentially zero power out of any laser cavity. You might want to re-think this.

I've done "the tests".

Good. I was wrong about you not doing them, and I apologize. Perhaps the laser you tested has a built in IR filter. That would explain your results.

 

[GooeyGus]

By your logic, you get essentially zero power out of any laser cavity. You might want to re-think this.

Are you missing something here?

The 1064 gets almost completely reflected back and fourth, yes you have losses which escape, very low mW's.

Your KTP is intracavity. When some of the light is doubled from 1064 to 532, the output coupler (or coatings on bonded crystal sets) are coated to completely reflect 1064nm back to the source to allow gain and lasing to continue. At the same time the output coupler is AR coated to allow the 532nm to pass, giving you a green laser, but reflecting the 1064 back to the source to allow lasing to continue. Make sense now?

In an ion laser, the HR mirror is coated to as close to 100% reflection as one can get, but you still get a few mW of waste beam out the back. At the same time, the OC is still coated for like 97% (or more) REFLECTION. This means the power inside the tube (or cavity) is HUGE compared to what is actually making it out of the laser. This is necessary for lasing to happen. It's the same with a green DPSS, the only difference being that the green light isn't sustaining the lasing, so it's allowed to 'exit'. The 1064 should be reflected as close as one can get to 100% at both ends of the cavity.

If the KTP weren't intracavity then yes you'd have a ton of 1064, but you also wouldn't have hardly any green light because you'd only be making one pass through the crystal.


What exactly did you use to measure the 22% 1064? I hope it wasn't an optical meter set at 1064, because any stray light of any other wavelength will hugely effect that power reading.

 

[Warske]

So...

I don't know if anyone is still interested in this subject, but I dredged this up out of Sam's Laser FAQ. It confirms some of my points, but also adds some interesting ones as well:

http://repairfaq.ece.drexel.edu/sam/laserdio.htm#dioapglp

Some totally invisible IR at 1,064 nm from the vanadate lasing process also leaks through the output mirror and its power may be similar to that of the green output!
...
If you have a green laser pointer and some means of detecting IR, the 1064 nm beam will be almost in the same position and with similar collimation to the 532 nm beam. However, the difference in wavelength will result in a change in effective focus/divergence and there is a 4.5 mR walkoff from the KTP of 532 nm beam with respect to the 1064 nm beam which will result in some discrepency in where they point. The 808 nm beam will be highly divergent/diffuse but may be quite intense next to the output.

Getting back to the OP's original question about the hazards of IR in lasers, this wikipedia article has some graphs involving acceptable exposure levels to different wavelengths and goes into some detail as to why it is set up this way. Interesting reading...

http://en.wikipedia.org/wiki/Laser_safety

 

[Ash]

So. Check this out.
It's a video of a guy shining a 2watt IR laser around a big city (Tokyo?) lighting up apartment rooms, and flashing signs and cars.
http://v.youku.com/v_show/id_XNzcxODAyNDA
WTF? How many people did this guy flash with IR (808nm) and they didn't even know it? I wonder if he caused permanent damage to some unsuspecting unfortunate people. Is this an example of laser irresponsibility?

 

[larrball]

So. Check this out.
It's a video of a guy shining a 2watt IR laser around a big city (Tokyo?) lighting up apartment rooms, and flashing signs and cars.
http://v.youku.com/v_show/id_XNzcxODAyNDA
WTF? How many people did this guy flash with IR (808nm) and they didn't even know it? I wonder if he caused permanent damage to some unsuspecting unfortunate people. Is this an example of laser irresponsibility?

Hey Ash,
I reposted this in the thread "A whole new level of idiot" in Multimedia.
Good find