[Laser] 820 nm laser safety for laser scatter experiments

[Jim Moss]

Class I is 1mW. (eye safe)
Large pupil size is 7mm diameter PI*r^2 = 38 mm2 (smaller than 1cm2).
Good to use the lower density rules for IR as there is no blink response as in
class IIIa for visible lasers. So use a density of 1mW per 38mm2 or about
3mW/cm2 or less.  With 3x extra safety... 1mW/cm2.

Jim
N9JIM/6

--- "aflowers at frontiernet.net" <aflowers at frontiernet.net> wrote:

> 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 -
> >
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