[Laser] Re: another lunar experiment

[F1AVYopto at aol.com]

>Is it not true that a collimated beam will  deliver the transmit power - 
>reduced only by absorption, and not by  inverse distance^2 - to a "spot" 
>on the lunar surface?  When the  spot then reradiates that energy, 
>essentially omnidirectionally,  inverse-distance applies as the power is 
>disbursed over an  ever-increasing-by square spherical surface area.  
>Isn't the  best-case round-trip attenuation then 1/distance^2, and a more 
>practical  path loss somewhere between 1/distance^2 and 1/distance^4?
>If an  Earth-borne mirror can reflect a solar beam that's less than the 
>lunar  disk at that distance, why would not essentially all of that 
>energy be  delivered to the lunar surface on the outbound path?

You are fully right  :
If the beam width is smaller the moon disc and if the receiver field  
intercepts all the circular spot on the moon, the 1/D² law do not apply on the  
direct way.
The 1/D² law applies only on the returning way.
The moon has a  very poor albedo (max 0,2 in the Tycho area) and the 
reflective properties are  lambertian.
The returning light is dispersed on a half spherical beam which  gives a 
fantastic loss. 
Yves F1AVY