[Laser] 6 beams in a CCR?

Tue Mar 10 14:19:45 EDT 2009

Hi all,
I assume I have a "nearly" parallel beam. A laser make this. Then a part
of the beam arrives mirror 1 will be reflected to mirror 2 and then
reflected to the 3. mirror (a very small part of the reflected beam can
arrive the second and the 3. mirror, but it is very small). That takes
place if the 1. mirror is overilluminated. For a parallel beam is this
effect an 2. order effect. This last mirror sends the incoming beam
exact in the direction of the incoming beam but lateral moved. The
beampropagation in a not "nearly" parallel beam is more complicated. I
believe, that each ligthbeam arriving one (or more) mirror(s)is reflcted
in the opposite direction if the incident angel of the incoming beam is
"nearly" normal to the entrance surface of the CCR. If the entrance beam
is away from normal incident or divergent, so you can get up to 6
reflected beams, thats right.

73 de Dieter - dl7udp -

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Today's Topics:

   1. Re: Laser newbie conner cube reflection question (James Whitfield)
   2. Re: Laser Digest, Vol 56, Issue 7 (Dieter Palme)
   3. Re: Laser newbie conner cube reflection question (James Whitfield)
   4. Re: Trihedral prism source? (James Whitfield)

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Message: 1
Date: Mon, 9 Mar 2009 17:47:07 -0600
From: "James Whitfield" <n5gui at cox.net>
Subject: Re: [Laser] Laser newbie conner cube reflection question
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Message-ID: <000701c9a111$5b63e880$6401a8c0 at Sony2G4>
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	reply-type=original

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

------------------------------

Message: 2
Date: Tue, 10 Mar 2009 11:14:37 +0100
From: "Dieter Palme" <dieter_palme at online.de>
Subject: Re: [Laser] Laser Digest, Vol 56, Issue 7
To: <laser at mailman.qth.net>
Message-ID:

<!~!UENERkVCMDkAAQACAAAAAAAAAAAAAAAAABgAAAAAAAAAQOWomd8r+kmlQR+dT/CHa8KA
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Hi Dex, you are right. In this distance of the CCR your pointer produces
a beam big enough to illuminate the hole CCR. Therefore all 3 mirrors
are in action in different ways and so you get 3 beams with different
phase relation and you see interferences between the 3 reflected beams.
73 de Dieter - dl7udp -

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Today's Topics:

   1. Laser newbie conner cube reflection question
      (W4DEX Dexter McIntyre)

----------------------------------------------------------------------

Message: 1
Date: Sun, 08 Mar 2009 23:35:01 -0400
From: W4DEX Dexter McIntyre <dmcintyre at att.net>
Subject: [Laser] Laser newbie conner cube reflection question
To: Free Space LASER Communications <laser at mailman.qth.net>
Message-ID: <49B48E65.1040501 at att.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

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

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------------------------------

Message: 3
Date: Tue, 10 Mar 2009 09:46:18 -0600
From: "James Whitfield" <n5gui at cox.net>
Subject: Re: [Laser] Laser newbie conner cube reflection question
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Message-ID: <000b01c9a197$5a64d120$6401a8c0 at Sony2G4>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original

Dieter,

One comment.  I believe that you will have six, not three "beams" coming

from the reflector.

Does anyone have the the calculations for how long a green laser would 
travel through air before the phase of a wavefront would become
completely 
randomized?  How then would the six independently random phase
relationships 
interact?

James
 n5gui

----- Original Message ----- 
From: "Dieter Palme" <dieter_palme at online.de>
Subject: Re: [Laser] Laser Digest, Vol 56, Issue 7

"...Therefore all 3 mirrors are in action in different ways and so you
get 3 
beams with different phase relation and you see interferences... 

------------------------------

Message: 4
Date: Tue, 10 Mar 2009 10:49:52 -0600
From: "James Whitfield" <n5gui at cox.net>
Subject: Re: [Laser] Trihedral prism source?
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Message-ID: <002201c9a1a0$3c0f6150$6401a8c0 at Sony2G4>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original

Jim

I tried to contact you offline.  I do not know if the message got to
you.

I was wondering if it would be possible to get pictures of the 12X12
mirror 
retro-reflector that you built.  Of particular interest is the method
you 
used to adjust the relative angles.

My attempts were rather crude and un-successful.  That probably was due
to 
my lack of imagination to "see" the solution.  I would like to see how
you 
approached the problem.

Thank you.

James
 n5gui

----- Original Message ----- 
From: "Jim Moss" <n9jim-6 at pacbell.net>
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Sent: Sunday, March 01, 2009 12:36 PM
Subject: Re: [Laser] Trihedral prism source?

James,
Agree with your inputs. I use the same items.
I recommend the stick on reflective tape. Pretty easy to use and attach.

I've built the 12x12 setup, and it works well, especially when the beam
has 
expanded to greater than the size of the reflectors, then you get "1"
beam 
back.
For adjusting, I used a screw/nut arrangement to hold the angles. This 
allows easy tweeking of the sides.

Jim
N9JIM

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