reflective light modulator

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7 total messages Started by Ken Thornton Mon, 22 Jun 1987 16:29

#7566

Author: Ken Thornton
Date: Mon, 22 Jun 1987 16:29

13 lines
912 bytes

Is there a material whose reflectivity can be modulated electronically?

This could be used in a telemetry system on a missile to modulate a
laser beam aimed at the missle from the ground with the material
formed as a corner reflector.

Earl Kirchner
(I'm borrowing use of this account)
-- 
     /\          
  /\/  \/\   
 / / /\/  \ Ken Thornton  {decvax,ihnp4}!uw-beaver!ssc-vax!ssc-bee!thornton   
/ / /  \   \

Re: reflective light modulator

#7567

Author: Ron Natalie
Date: Tue, 23 Jun 1987 14:15

11 lines
864 bytes

How about liquid crystals?  Seems like you ought to be able to place
a sheet in front of the corner reflector which would also keep dirt
off the mirrors as well

          LCD-material
                  V
                  |\
Beam              | \
----------------> |  > <- corner reflector
                  | /
                  |/

Re: reflective light modulator

#7568

Author: Carl Witthoft
Date: Thu, 25 Jun 1987 11:37

31 lines
2001 bytes

In article <845@ssc-bee.ssc-vax.UUCP> thornton@ssc-vax.UUCP (Ken Thornton) writes:
>Is there a material whose reflectivity can be modulated electronically?
>
>Earl Kirchner
>(I'm borrowing use of this account)
This is klugey, but quick:
IF you happen to have a polarized beam or at least a well-collimated and
coherent beam, 
	1) put a retro behind a pockels cell. Whack the drive voltage to
adjust cell transmission, and retro will reflect light back thru system. 
This has problems w/ holding appropriate xmsn. Forget it.
	2) If an acousto-optic cell is useable, then you can control the
diffraction efficiency of the cell and place the retro optics in the diffracted
beam path. Thus, if cell is off, R=0 ; if on R --> 1 .

What might be interesting,too, if you have a grad student to beat on, is
investigating some piezo-electric material in an evanascent (sp) wave
setup. My weird idea is: in "off"state, piezo is "far" from second prism
element, and total internal reflection takes place. In "on" state, piezo 
expands and contacts the second element, so transmission takes place.
Hmmm.. has anybody ever done anything like this?


-- 

Alix's Dad ( Carl Witthoft @ Adaptive Optics Associates)
{ima,harvard}!bbn!aoa!carl
{wjh12,mit-vax}!biomed!aoa!carl
54 CambridgePark Drive, Cambridge,MA 02140 617-864-0201
" If you're not afraid you're going to die on your windsurfer,
the wind isn't high enough to have a good time."

Re: reflective light modulator

#7569

Author: Carl Witthoft
Date: Thu, 25 Jun 1987 11:40

26 lines
1589 bytes

In article <12862@topaz.rutgers.edu> ron@topaz.rutgers.edu (Ron Natalie) writes:
>How about liquid crystals?  Seems like you ought to be able to place
>a sheet in front of the corner reflector which would also keep dirt
>off the mirrors as well
>
>          LCD-material
>                  V
>                  |\
>Beam              | \
>----------------> |  > <- corner reflector
>                  | /
>                  |/

Can this work? I'm worried about two things: 1) polarization changes
as beam bounces off corner cube, and resultant mess w/ polarization sensitivity
(if any) of LCD, 2) I hear LCD's can't run DC, so need to pulse the beam
on&off at some rep rate, which may not be acceptable.

-- 

Alix's Dad ( Carl Witthoft @ Adaptive Optics Associates)
{ima,harvard}!bbn!aoa!carl
{wjh12,mit-vax}!biomed!aoa!carl
54 CambridgePark Drive, Cambridge,MA 02140 617-864-0201
" If you're not afraid you're going to die on your windsurfer,
the wind isn't high enough to have a good time."

Re: reflective light modulator

#7570

Author: Ron Natalie
Date: Fri, 26 Jun 1987 20:05

9 lines
973 bytes

Well, I don't have a corner reflector around (there used to be one
in the office down the hall, but down the hall is 150 miles away), but
intuition tells me that a corner reflector should not change the
polarization of the forward beam with respect to the reflection.

Yes, you're going to have to provide a low AC modulation (HZ) or so
but you can generate that with a little oscilator like a 555.

-Ron

Re: reflective light modulator

#7571

Author: Henry Spencer
Date: Sun, 28 Jun 1987 02:36

14 lines
1281 bytes

> >How about liquid crystals?...
> 
> Can this work? I'm worried ...
> ... I hear LCD's can't run DC, so need to pulse the beam
> on&off at some rep rate, which may not be acceptable.

The excitation signals to LCDs can't be DC (or an AC signal with much of a
DC component) for any length of time without damaging the LCD.  But as I
understand it, this does not imply that the LCD's optical properties pulse
in time with the signal.  LCDs don't care about polarity, and their response
time is quite slow, so the AC signal produces pretty much a DC result.
-- 
Mars must wait -- we have un-         Henry Spencer @ U of Toronto Zoology
finished business on the Moon.     {allegra,ihnp4,decvax,pyramid}!utzoo!henry

Re: reflective light modulator

#7572

Author: Henry Spencer
Date: Sun, 28 Jun 1987 02:37

7 lines
923 bytes

> Well, I don't have a corner reflector around (there used to be one
> in the office down the hall, but down the hall is 150 miles away)...

Quite a hallway you've got there, Ron!
-- 
Mars must wait -- we have un-         Henry Spencer @ U of Toronto Zoology
finished business on the Moon.     {allegra,ihnp4,decvax,pyramid}!utzoo!henry

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