[Laser] Trihedral prism source?

[James Whitfield]

May I suggest you first look at your local auto parts or hardware store?  If 
you look at the reflectors for mounting on vehicles, you will notice that 
they are sheets of many trihedral prisms joined together, each about 1/8 
inch on a side.  The most common reflectors are round, but they are also 
available oblong.  I believe they come in 3" and 4" sizes.  As I recall they 
are available in "clear" as well as red and "amber", which I think of as 
yellow.  In the experiement I have done the yellow seem to give a brighter 
reflection of the red laser pointers and LEDs that I use, but I would have 
expected the clear or red ones instead.  The effect might not be "real" if 
you can measure such things with an instrument instead of just the way 
things "look" to my eyes.

Depending on your application, you might be able to use the reflective 
characteristics of street signs.  I use the STOP sign down at the end of my 
block for a lot of testing.  There is also a smaller sign across the street 
from it that is green with the street name in white letters, which work 
nicely if I need a smaller, uncolored target.  They are made with 
retroreflector beads, but are not trihedral prisms.

Another option you might consider is assembling three square mirrors, each 
perpendicular to the others.  It is not a particularly easy task, at least 
not for the attempts that I have made with 4 inch mirrors from a hobby and 
craft store.  A rather makeshift attempt had limited success when I put I 
put the three on a plastic picture frame cube and used duct tape to secure 
them in the right shape.

I have thought of a version made with 12" mirror tiles mounted in a wooden 
frame made from 2X14 lumber.  I know that it will need some means to "tweak" 
the relative angles, but I have not figured that part out.  I can tell you 
that if you shine a light into it, out will come six (6) trianglular shaped 
reflected beams.  The goal of alignment is to get all sixe to come together. 
I had thought that a preliminary alignment could be done with a flashlight 
inside my basement shop / "optical range", and then critical alignment done 
outside with a laser pointer for the light source.

If you prefer to shop for a commercial prism, try a web search for the terms 
"retroreflector" and "corner cube".  The least expensive one I know about is 
on Surplus shed, Item number L3755 for $17.50, but it may not be suitable 
for your purpose.

I hope this will help you.


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 01, 2009 8:56 AM
Subject: [Laser] Trihedral prism source?


> Looking to find a trihedral prism at a reasonable price for some
> experiments.  High quality is not important.
>
> W4DEX