From: "Suzy Jackson" 
To: "Ken Hunter" ,
        "Jerald F. Wright" 
Cc: 
Reply-To: "Suzy Jackson" 


Ken Hunter wrote:

> Several years ago there were experiments made of bouncing a laser beam
> off of the retro reflectors left on the moon by the Apollo astronauts. The
experiments were designed to measure the
> distance changes between the Moon-Earth. If I recollect properly the
scopes used were in the 12-16 inch category and the
> lasers were fairly low power (like the kind you find in the old Super
Market scanners).

This is incorrect.  I worked for four years at Orroral Satellite Laser
Ranging Observatory, which was originally set up (in 1974) for Lunar laser
ranging.  We used a 1.5m diameter telescope, with a laser that occupied a
bench about 2m long and 1m wide.  It delivered 100mJ pulses of green
(532nm) light in a 100ps pulse (1Gigawatt peak).  That's a far cry from the
1 to 5 watt CW lasers used in barcode scanners and laser pointers.

The newer "eyesafe" systems typically use less energy per shot
(~1mJ) but run at kilohertz pulse rates, rather than the 10 odd Hz rates of
the old systems.  FWIW, one of these stations currently operates on Mount
Stromlo, alongside a number of optical telescopes.

Lasers have very obvious warning signs on them, and are classed according
to their potential for damage, from class 1 to class 4.  Class 1 lasers are
eyesafe, in that you can hold one to your eye and stare into it.  Class 1a
lasers are also eyesafe, in that the power level is high enough (and in the
visible spectrum) to make you blink, and the energy received in the time
before your eye closes isn't enough to cause damage.  Class 2 lasers are
more powerful, etc.  Ours was a class 4.

Laser pointers, whilst potentially annoying, are not a significant eye
hazard, unless they're viewed through a telescope or binoculars.  People
seem to have an irrational fear of lasers, similar to that of microwave
ovens and mobile phones.

Regards,

Suzy

-+-
Suzy Jackson        suzyj{at}bigpond.com        http://www.suzyj.net

--- BBBS/NT v4.00 MP