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Effect of Polarized Lens on Laser Output

Keiferson22

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Hey all, I have a class 3R laser. I am using it to project the line of fire (barrel axis) of a weapon. In order to get rid of all of the messy diffused light associated with the laser spot I have chosen to pass the beam through two orthogonal polarized pieces of film. This has drastically reduced the intensity of the light but reduced the beam width by half which makes it more accurate for my application at very short distances.

Long story short, a safety review board was held to review my activity. A member of the board who is the "laser rep" started that I could not use a filter because I was focusing the beam. I think he misunderstood that the narrowing of the beam was a secondary effect of using the filter.

In my mind it's seems simple, if I can clearly see that the transmission level (intensity) is drastically reduced, then the laser output should be somewhat reduced as well.

Can someone back me up with an equation, law or principal? Or are I dead wrong? Shouldn't the output be reduced to a quarter of the original intensity?

Thanks in advance!
 



Cyparagon

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Two orthogonal polarization filters should block nearly all light, laser or not. The reduced intensity means you can't see all of the dot since the dot intensity follows a Gaussian distribution, and the 'edges' of this distribution will no longer be perceived visually.

Barring some crucial details you may have left out, I think you're technically correct here. But I don't see why polarization filters are the best choice. One issue may be if the filters are not mounted perfectly, the refraction may steer the beam away from the initial target. I also don't see the need for added complexity, as this introduces more potential failure points for minimal return.
 

Keiferson22

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Two orthogonal polarization filters should block nearly all light, laser or not. The reduced intensity means you can't see all of the dot since the dot intensity follows a Gaussian distribution, and the 'edges' of this distribution will no longer be perceived visually.

Barring some crucial details you may have left out, I think you're technically correct here. But I don't see why polarization filters are the best choice. One issue may be if the filters are not mounted perfectly, the refraction may steer the beam away from the initial target. I also don't see the need for added complexity, as this introduces more potential failure points for minimal return.
From what I can tell, at very long distances even, the beam direction seems very unaffected by errors (even large ones) whereby the plane on the filter is not perfectly perpendicular to the beam axis.

This seems to be a good simple solution for my application. Overall goal being to minimize the diffuse scatter around the laser spot so that I can more accurately find the center of the laser spot.

The filters are housed in a special cap that fits over the laser housing.

See images below that show before and after.
 

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RedCowboy

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Why not use a spatial filter ? I like a cleam beam myself and a tube with 2 or 3 spatial filters can help a lot, especially for any wide angle splatter/lens flair.
 

Keiferson22

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Not to be snarky, but I have a solution already. My goal is to just show that it's safe i.e. use physics to show that I'm correct in my assumption.
 

Encap

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You need a Laser Power Meter to determine the real world mW output of a laser. There is no physics that can show safety of what you are doing without knowing the output in mW, wavelength and divergence--nothing you have told on LPF about what you are doing allows or means anything about safety of what you are doing or calculating same---no data other than perhaps a vague general statement that you are using a filter to reduce the output power --no data is no data
Filter or no filter is meaningless safety wise w/o any data/characteristics, Am speaking about just 1 piece---a whole bunch of them ganged together is far less safe in terms of capacity for a laser accident if that is what you are doing. Any laser item for sale or use in the presence of other people, not just you at home, in USA must meet all the FDA requirements/laws/rules/regualtions. There are no loopholes concerning same. See: https://www.fda.gov/radiation-emitt...nment-products/laser-products-and-instruments
Laser Hazard is based upon output power of lasers, wavelength and divergence.

If the output is >5mW what you are doing is not eyesafe/not safe which is why US FDA limits all battery powered hand held laser to <5mW. Other Countries limit to 1mW. Even those low outputs can cause eye damage unde certain circumstance.
FDA laws, rules, and reguations---" 21 CFR 1040.11(b) and 1040.11(c), limit surveying, leveling, and alignment, and demonstration laser products to Class IIIa. This means that pointers are limited to 5 milliwatts output power in the visible wavelength range from 400 to 710 nanometers. "
See: https://www.fda.gov/radiation-emitt...rtant-information-laser-pointer-manufacturers

See laser hazard chart here: https://www.lasersafetyfacts.com/resources/FAA---visible-laser-hazard-calcs-for-LSF-v02.png
See explaination of hazards for each class of laser here: https://www.lasersafetyfacts.com/classes-menu.html

if you want to calculate eye hazard see how to do here: https://www.laserpointersafety.com/safetycalcs/index.html
 
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Keiferson22

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Yes I understand all that and the government has already done a study of this particular laser and all that data is available. This is a non-eye-safe laser. I have glasses for this particular wavelength.
 

steve001

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Yes I understand all that and the government has already done a study of this particular laser and all that data is available. This is a non-eye-safe laser. I have glasses for this particular wavelength.
It seems to me this safety representative misunderstood your incorrect terminology.
What you have done is attenuate the beam intensity. Advise this representative what you did.
 




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