[Laser] Freespace Laser Surplus Device Source

[F1AVYopto at aol.com]

Dans un e-mail daté du 17/05/2007 17:30:31 Paris, Madrid (heure d'été),  
aa6eg at hotmail.com a écrit :
>Add or subtract the "movement" whether done  
>electronically or mechanically,  and you know what fraction of a  wavelength 
>you are located, but don't know the total integral number of  wavelengths.  
>Do this for 3 carefully chosen frequencies, and you  can determine the 
actual 
>line length.

Pat,
This technique has  great advantages because the rather low frequencies laser 
modulation (20 MHz),  the continuous wave mode and the low peak power.
This ranging technique is  certainly very efficient on a fixed target.
I think it is not used for Moon  ranging because the librations movements.
The moon ranging needs picoseconds  ultra high power laser pulses.
The RX bandwidth must to be extremely large  and a cooled avalanche 
photodiode in Geiger mode is mandatory.
The aiming must drive the laser spot on one of the Apollo  reflectors.
On the moon the spot must be less than 10 Km in diameter.
In a 120 cm telescope 1 photon is received for 10^20 sent !
For 100 laser shots less than 5 good echoes are received !
We have an  EME project with a VLF modulated 2W infrared laser and two 30  cm 
telescopes.
The goal will be only to detect a bounced signal evidence  after a very long 
FFTDSP computing time.
The RX will be a cooled (-40°C)  K3PGP RX with a narrow band optical 
dielectric filter to reduce earth-light in  the dark area out crescent.
Because the small 30 cm TX telescope and the infrared CWM laser diode  
junction structure, the "spot" on the moon will be a thin rectangular area  (about 
120 x 10 Km) and so it will be not possible to use efficiently the Apollo  moon 
ranging reflectors.
We expect the best IR albedo areas (0,2 versus the  Clementine LIDAR maps) 
near the Ticho ejectas will be sufficient to bounce a few  photons each second 
to the RX telescope...
If the moon is a lambertian reflector our calculations give a small  
detection probability after more than one hour of FFTDSP integration in 1/100  Hz.
We have some chance to succeed because we do not know it is impossible !  (HI 
x 3 ! )
73 Yves F1AVY