[time-nuts] Using lasers for data transmission

[jimlux]

On 5/1/16 3:22 AM, Bruce Griffiths wrote:
> The solution with high power is to use a beam expander so that the unaided eye cannot collect a power greater than the safe limit. Using near IR beams also helps.
> Bruce
>

IR is a problem for eye safety, because IR doesn't trigger the blink 
reflex, so you can inadvertently "stare into the laser with the 
remaining good eye".


If you want to stay below, say, 1 mW/square cm, and you're running a 20 
mW laser, you'd want 20 square cm of aperture.  That's about 5cm diameter.

You should bear in mind that if you're doing "mountain top to mountain 
top" type applications there might be someone looking at you with 
binoculars or a telescope, which makes their "light gathering aperture" 
much larger, and increases the risk of injury.