[Laser] comments about Moon pictures

[Joe Fitzgerald]

One neat trick you can use for lasercom in space is to use a Q-switched 
YAG laser.  The Q-switch allows one to dump the energy stored in the 
laser cavity in a very short burst (on the order of a nanosecond) at 
very high power (multiple kW), even if the laser would average only 
though the average power consumption of the laser is 10W or less.  This 
makes the detection problem a lot easier.  Information transfer is done 
by pulse position modulation.  For example, take some time interval like 
a second, and break it up into 256 intervals.  Fire your laser during 
one of those intervals to send your information.  When you demodulate, 
just figure out which 1/256 second time slot the laser fired in, and you 
get 8 bits from that single pulse.    This is essentially the scheme 
NASA is planning to use for Mars-Earth downlink in the coming years.

-Joe KM1P