[Laser] APD diodes in Geiger mode

[KY1K]

Also, don't get too excited about the Geiger mode. It does little to 
enhance the actual ability to hear a weak signal. IMHO, it is nearly 
useless, it is nothing more than a gate that allows output during the 
period of interest.

If one points any APD at the Moon, they will get many periods of 
'false positive' indications because anyway you look at it, there are 
going to be many photons coming from the Moon whether it's 
illuminated with our laser or not.

By making the gating timing very brief, we can slightly increase the 
likelihood that the photon burst heard is due to our laser. But, you 
also need to evaluate how many false positives you get if you use the 
same gating timing with the laser transmitter turned off::> This 
issue is a point often overlooked when people use gated APD's or PM tubes.

Regards,

Art




>>Does anyone have any experience with Geiger mode silicon diodes or 
>>with silicon APD's operated in Geiger mode?  (not all APD's will 
>>work in Geiger mode)
>>
>>
>I have a little.  I got mine from Advanced Photonics 
>http://www.advancedphotonix.com/ around 6 years ago in an effort to 
>build a reciever for AMSAT OSCAR 40, but my project kind of died 
>when the spacecraft died.  Save your pennies, they go for about $200 each.
>As I understand it, the "Geiger mode" APD's are simply selected out 
>of the regular APD batches the quietest ones.
>-Joe KM1P