[sci.electronics] reflective light modulator

thornton@ssc-vax.UUCP (Ken Thornton) (06/22/87)

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   
/ / /  \   \

ron@topaz.rutgers.edu (Ron Natalie) (06/23/87)

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
                  | /
                  |/

carl@aoa.UUCP (Carl Witthoft) (06/25/87)

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."

carl@aoa.UUCP (Carl Witthoft) (06/25/87)

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."

ron@topaz.rutgers.edu (Ron Natalie) (06/26/87)

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

henry@utzoo.UUCP (Henry Spencer) (06/28/87)

> >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

henry@utzoo.UUCP (Henry Spencer) (06/28/87)

> 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

daveb@eneevax.UUCP (David Bengtson) (07/01/87)

In article <8215@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes:
>> 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

The corner reflector is obviously there so that the Maglev train for 
coffee breaks can tell that it is approaching the end and take approp.
action ( :-) )