[Laser] pulse modulation

[Joe Fitzgerald]

TWOSIG@aol.com wrote:
 For the same amount of 
> power, over the same amount of time, and with the same amount of data transmitted, 
> does the YAG laser have an advantage?  And what is that advantage.  The only 
> thing that seems obvious to me is that a laser (and it would not have to be Q 
> switched YAG ) can be made to send a much more narrow beam of light with a 
> telescope of a more manageable size, than a radio wave.  Is it theoretically the 
> same amount of data that can be transmitted in a fixed amount of time with a 
> specified amount of power?
> 

Theoretically, yes. Shannon's Law states 

c = b log2 (1 + s) 

where c is channel capacity (e.g. bits per second), b is bandwidth and s is signal to noise ratio.  As you stated you can make a very narrow beam in a small package to help maximize s.  And with lasers, you can get tremendous b (short pulses = wide bandwidth).


For some hard core analysis see:

http://tmo.jpl.nasa.gov/tmo/progress_report/42-109/109L.PDF


-Joe KM1P