[Laser] Trihedral prism source?

[Pat Barthelow]

Hello Joe, 
 
I once tested various plastic highway reflectors and other reflective materials for use as inexpensive retroprisms for early Surveying EDM equipment.
(Geodimeter, HP, mid-late 70's) 
Both visible light,  red laser and IR wavelengths.
 
We found that the round white plastic highway reflectors worked, with a fair amount of returned signal variation  between styles and brands.


I remenber that, generally, the 3" disks whose molded plastic retroprism arrays, probably about 1mm in size,  were laid out with two halves per disk, worked better (longer range) than the ones with,say, 6 or 8 wedge shaped ones at different orientations,  in the circular disk.
 
Modern Surveying rage poles often carry a very small cut crystal reflector, perhaps 1" face dia and while not ham cheap, are reasonable for commercial use.
 
AGA the glass maker from Sweden  (orig expert in Lighthouse cut glass Fesnel Lenses) used to make precision surveyors EDM corner cubes, about 2.5" face diameter with mutual face perpendicularity of 1/2" second of arc, but a set of 3 was more than $600 US$ back in 1971.
 
Googling, I just found that the industry terminology is 
Highway delineation reflectors, with a large number of suppliers.
 
Some time back, I picked up  a Harbor Freight laser carpenters level, with a 3 mw visible laser, and went to the top floor at night,  of the Montery  Mariott Hotel to see how far I could see the spot, both on the ground and at reflectorized surfaces,
(Verry careful not to illuminate people, especially those driving cars, or airplanes)  such as stop signs, and  reflectorized, glass bead street signs. 
 
I was surprised that even a mile away, the reflection from a glass bead/scotchlight surface sign was easily seen with the unaided eye.  
 
Also, California License plates have a white reflectorized background, and they produced brilliant returns a mile away.

 

There is a good application of thin surface retro-reflectors at:

http://tmo.jpl.nasa.gov/progress_report/42-147/147I.pdf

See figures 2, and 4.

 

best,  Pat, AA6EG  apolloeme at live.com


 

> Date: Sun, 1 Mar 2009 09:56:24 -0500
> From: dmcintyre at att.net
> To: laser at mailman.qth.net
> Subject: [Laser] Trihedral prism source?
> 
> Looking to find a trihedral prism at a reasonable price for some 
> experiments. High quality is not important.
> 
> W4DEX