[time-nuts] Using lasers for data transmission

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 1 May 2016 15:02, "Bruce Griffiths" <bruce.griffiths at xtra.co.nz> 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

It is a long time since I worked with lasers, so my knowledge is both out
of date and my memory not perfect. But I was a long while ago regularly
using and sometimes aligning a picosecond pulsed laser at about 800 nm. The
average output power was 1 W, so a very dangerous class IV laser. It
certainly hurt if one had the beam on ones skin, but it was not
sufficiently powerful to noticeably burn the skin if one did the obvious
thing and moves ones hand away.

But I believe people need to be particularly careful using IR lasers. The
lens in the eye will not focus Iinfra red on the retina,  so that is
probably why you say IR is safer. However one of the protective methods the
eye has is a "blink response". One blinks if one perceives a light source
as bright. Blinking offers some protection to the eye. But since one does
not see an IR laser source, one  does not blink, so IR lasers disable one
of the eyes protective mechanisms.

Hence there are various complications that arrive when discussing laser
safety issues.  I don't have the knowledge to advise on what is or not
safe,  but will warn there are several effects which are important,  and
many people don't realise this.

Laser safety is a nontrivial subject.

Dave.