IR Filter Question: Perceived Brightness Affected or Not?

There was a discussion brewing in another thread that I had started about a recent laser purchase, and it got to a point where we were going off on tangents about IR filters.

So I decided to create this thread and ask the very same question here to see what kinds of responses it will generate.

The question was:
"So, just to be absolutely clear on this...
Will the IR filter simply just block out the IR and not affect the perceived brightness of the green light in the laser in any way whatsoever?

So basically, blocking out the IR will just limit the burning capabilities of the laser by ~ 70mW, but the brightness when shined will remain the same? "

I would be very interested to hear your thoughts and for you to share your experiences.

I'm not sure where you got the ~70mw figure from.
The IR filter will just limit the burning capabilities of the laser by whatever amount of IR the laser was putting out before you added the filter.

So, if your unfiltered laser was outputting:
- 250 mW of 532nm GREEN
- 50 mW of IR
That laser would register 300 mW on an LPM and have 300 mW worth of "burning potential"

If you then added an IR filter, your laser would output:
- 250 mW of 532nm GREEN
- 0 mW of IR
That laser would now register 250 mW on an LPM and have 250 mW worth of "burning potential"

In both cases, the 532nm GREEN light is 250 mW, and in both cases, that laser will appear the same brightness. Your eyes don't pick up infrared light (for the most part), so the IR doesn't contribute to a 532nm DPSS green laser's perceived brightness. Thus, the absence of IR doesn't take away from it.

One "small technicality" might be that an IR filter (well, pretty much any piece of glass) will have some small incidental effect on even the wavelength it is NOT filtering. So of that 250mW of 532nm GREEN light, you might loose some imperceptible tiny amount of 532nm light simply because you've placed one additional item in the beam's path. But that's a negligible consideration that you'd really never worry about in practice.

hamidxa said:

The question was:
"So, just to be absolutely clear on this...
Will the IR filter simply just block out the IR and not affect the perceived brightness of the green light in the laser in any way whatsoever?

So basically, blocking out the IR will just limit the burning capabilities of the laser by ~ 70mW, but the brightness when shined will remain the same?

I would be very interested to hear your thoughts and for you to share your experiences.

Click to expand...

Assuming your filter does not also block a significant portion of the green light, the green output should remain the same. Remember that there are no perfect optics, so a small percentage of light will be reflected and absorbed by the glass. High quality optics with anti-reflective coatings minimize losses to a very small %.

Also, in my experience, excess IR does not greatly contribute to the burning power of a green laser. Usually the amount of IR that spills out is only a few tens of milliwatts and it is never collimated in a tight beam like the green output.

IR and green have different wavelengths, and therefore will not focus down to the smallest spot at the same distance from the lens at the same time. Hence, that IR contributes very little to the 532nm maximum energy density waist

Thanks for all of the replies everyone.

I was really going after maximum brightness per dollar rather than wanting to invest in burning power.

Therefore, I was really hoping that the 400mW rating of this laser (LZSK - 532nm 400mW Green Laser Pointer w/ Case + Goggles) would have been based solely on the green light emitted rather than be a combination of green + IR, but it's still the best bang for the buck out there that I've found.

On that note, how does the Lazerer 400mW in question stack up against these (300mW ones) from Wicked Lasers?
100mW, 200mW, & 300mW Laser in Red, Green, & Purple | E3 Series Lasers
Green Laser Pointer 1 Watt | S3 Krypton | Spyder III | Wicked Lasers

Are the WL ones considered to be "true" 300mW lasers in the sense that the 300mW rating is made up of Green only (i.e., IR is not factored into their power rating)?

P.S. I got the ~ 70mW IR figure from this review: http://laserpointerforums.com/f52/r...green-laser-pointer-w-case-goggles-67415.html

hamidxa said:

Thanks for all of the replies everyone.
On that note, how does the Lazerer 400mW in question stack up against these (300mW ones) from Wicked Lasers?

Click to expand...

Whoah, whoah and WHOAH. Do not buy a "Wicked laser". They're a complete rip off. If it ever arrives it will die within a couple months. They're a bunch of scammers, and I'm saying this from personal experience