[Laser] pulsed laser 101

[Art]

Greetings all,

I've had a most enlightening week, and I need some suggestions on 
pulsed lasers.

In a nutshell, I got into an email discussion with a highly 
experienced DSP person regarding very deep FFT sound card analysis 
for extremely weak laser signals. In the course of examining the 
ultimate limiting factors in FFT, the person suggested that I might 
be able to receive weaker signals using pulses, with the receiver and 
the transmitter synchronized and by using averaging to add the 
results of each repetition together (rather than tossing out the 
previous samples as Is done for FFT).

Obviously this requires a wideband optical front end and short 
pulses. And, the wideband front end will let in much more noise than 
a narrow band front end like most of us use.

But, by adding the time synchronized results of each cycle together 
(averaging), the desired signal will slowly 'grow' out of the noise.

I was considering FFT with .001 Hz (or .0001 Hz) bins as being the 
ultimate weak signal mode........

But, after this email exchange, I began to wonder if this time 
synchronized (both rx and tx) with averaging method would provide 
better weak signal reception (better than deep FFT)? In terms of the 
receiving system, the pulsed laser receiver is much easier to 
fabricate for sure!

But which method is likely to provide better ability to dig out weaker signals?

Also, does anyone have suggestions on how to produce very short 
pulsed lasers at 850 nM (to coincide with photodiodes best 
sensitivity)? Regarding the pulsed lasers, I can only think of the 
old stud mounted pulsed diodes, but perhaps there is another method 
that is practical.

All comments appreciated.

Art