[Laser] Laser newbie conner cube reflection question

[James Whitfield]

Dex

I am not so experienced that I would want to try to "explain" what you are 
seeing.  This might give you a little more insight.  I suggest that you get 
a simple mirror, front surface would be good but, I think a second surface 
mirror will give you a similar result.  Make sure the mirror is larger than 
the "dot" produced by the laser pointer at the distance of the mirror.

Compare the reflection that you get with the standard mirror to what you get 
from the corner cube, and then compare than to the "dot" you get directly 
from the laser pointer at an equivalent distance.  ( If it is 250 feet from 
the laser pointer to the mirror and then 250 feet from the mirror to your 
observing surface, then the "direct" distance should be 500 feet.  Scale 
things down if you need to. )

My guess is that you will get the same concentric circles on all three 
conditions, direct, flat reflection, and corner cube reflection.

Another "experiment" you might try is to make a "mask" of stiff paper with a 
hole that matches the size and shape of the corner cube.  Set it in front of 
the flat mirror to see if that produces the same size and shape reflected 
dot as the cube.  You might also get the same result if you shine the laser 
through the mask ( at 250 feet from the laser ) on a view surface 500 feet 
from the laser.

Best Wishes.


James
 n5gui





----- Original Message ----- 
From: "W4DEX Dexter McIntyre" <dmcintyre at att.net>
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Sent: Sunday, March 08, 2009 9:35 PM
Subject: [Laser] Laser newbie conner cube reflection question


>I now have a trihedral prism, conner cube or retroreflector (are there
> any more names for the device?)  Using a 5 mw green laser pen with the
> reflector set approximately 250 feet away I get an interesting
> reflection. The reflection is about an 8 CM diameter from the 4 CM
> diameter cube with very noticeable concentric circles.  I tried to
> photograph the display but was unable to get the exposure right to see
> the circles.
>
> http://w4dex.com/laser/laser_250ft.jpg
>
> I'm guessing this is created by phase cancellation but so far I haven't
> been able to confirm this with Google.
>
> Dex