[Laser] 820 nm laser safety for laser scatter experiments

[aflowers at frontiernet.net]

Kerry,

You can do a rough calculation knowing the diameter of the pupilto be
1cm^2.  Even at full dilation I don't think most human pupils would be
quite this big.  Obviously a beam larger than this cannot have all of
it's power focused onto the retina.  Most lasers don't have equal power
distribution over the entire diameter, but you may want to look for the
highest power density in a 1cm^2 cross-section of the entire beam. 
That should get you in the ballpark.

A good way to do this might be to take a relative power measurement with
a 1cm^2 photodiode hooked up to a power meter.  Measure a known power
from a laser pen or better yet a 5mw source at the same wavelength. 
You know all of that energy is striking the active surface.  Then place
it in front of your higher-power expanded beam and look for the highest
reading.  This should get you in the ballpark.

Andy K0SM/2





Quoting Kerry Banke <kbanke at qualcomm.com>:

> Can someone on the reflector give  a quick tutorial on laser safety
> for
> doing 820 nm laser scatter experiments?  How large does a laser beam
> of a
> specific power need to be expanded to be considered eye safe?
> Thanks - Kerry N6IZW -
>
> _______________________________________________
> Laser mailing list
> Laser at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/laser
>