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ArcticMyst Security by Avery

focused green laser

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Jun 14, 2014
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hi all this is my first post, and i have a question.

im new to lasers, and i recently got myself a 5mw green laser for star pointing. when i was playing around with it, i attached a small lens to it and i was able to focus the beam to a very narrow point, i roughly estimated the beam to be anywhere between 0.1 to 0.2 mm, i cant get more accuracy.

when i plugged in the numbers, the power density at that point is about 3100 W/cm2, thats about the same as a 150mw laser with a 1.1mm beam width....

so the question is, is that a high enough power density for me to use goggles?
 





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Jun 20, 2013
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It should be 125mW/cm^2 and no, you shouldn't need goggles unless it was pointed at your eye.
 
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What is lpd? and "P"?
I also made a mistake.

I'm assuming .2mm is the dot diameter
So:
(.01cm)^2 x pi = .000314cm^2
.005W/.0003143cm^2 =

15.9W/cm^2 or .159W/mm^2
So 159mW per square millimeter
 
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that does make sense, but thats quite a bit higher than 125mw that you originally calculated, is that enough power to use goggles?
 
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Don't forget there is also a power loss passing through the additional lens.

Alan
 
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that does make sense, but thats quite a bit higher than 125mw that you originally calculated, is that enough power to use goggles?

I forgot to convert from mm^2 to cm^2
so the 125mW/cm^2 should have been 125mW/mm^2
 




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