[Laser] pulsed laser 101

[F1AVYopto at aol.com]

Hello Art
 
>But, I wonder if this type of experiment would allow us to prove the  
>concept before moving up to expensive APD's, and much higher sampling  
>rate A to D converters?

To display a  pulsed LED or long time laser pulse (from 0,05 to 1 
millisecond) you can  use the "time domain scope" from the DL4YHF Spectrolab  program.
 
The  two channels for stereo must be set. 
One of them  stays the signal input. 
The second  must be the "external synchro scope" and must be supply by a 
divided  quartz oscillator. 
Another divided  quartz oscillator with lower dividing range must be used to 
synchronise the  pulsed optical TX. 
Use the  highest sampling rate your sound card can do. 
Use the  scope average function at its max value to display the  pulses. 
But the  results are poor: 
The sound  card anti-aliasing input filter reduce dramatically the useful  
bandwidth. 
The long  averaging needs the two quartz oscillators (TX RX) with frequencies 
as near  as possible one of them. 
The pulses  can be well seen by this way after a few minutes but a well 
adjusted high  speed threshold detector fitted just after the optical front end  
seems often more sensitive.... 
Have good  experiments. 
73  Yves