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Old January 29th 05, 03:11 AM
Larry Dighera
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On Fri, 28 Jan 2005 23:35:34 +0000, 10Squared
wrote in ::

Larry Dighera wrote:

On Fri, 28 Jan 2005 11:53:03 +0000, 10Squared
wrote in ::

Laser device in question has a rated power of 5 mW.


Actually, some are available with over 10 times that power:
http://www.wickedlasers.com/products.php

However, as you assert, they are probably still incapable of
inflicting retinal damage at the distances involved when aimed at an
aircraft in flight.


OK, let's see what happens with their most wicked laser. I see the Extreme
Phoenix with a power rating of 500mW.


Just to be accurate, I believe the Wicked laser diode is RATED at
500mW, but the claimed output is 70 to 80 mW, IIRC.

The quoted beam divergence is 1.2 mrad. Assuming a distance of 1 km,

a = 1.2 mrad
tan a = x / 1 * 10^3
x = 10^3 * m * x tan a
tan a =~ a
x = 1.2 * 10^3 * 10^-3 * m = 1.2 meters

To be conservative, let's use the beam divergence of only .5 mrad, or .5
meters at 1 km:

.5 m = 50 cm
p = 500 mW / (3.141 * 25 * 25 * cm^2)

Your 500 mW laser has a power of about .25 mW/cm^2 at 1 km. Again, much less
than the MPE for constant exposure.


Intuitively, I didn't question that, but thank you for the formulae.

That brings up another point: Who is going to stare at a laser? Brief
exposure is uncomfortable and will cause you to look away quickly, so
MPE equation #2 is probably the one that applies.


So you're saying that closing one's eyes or looking away is reflexive.
What length of time would you estimate it takes for that reflex to
occurr?

What magnitude of laser power would you estimate to be required to
cause retinal damage at say 1 mile for what period of time?