Path: utzoo!mnetor!uunet!husc6!bbn!mit-eddie!ll-xn!ames!killer!convex!authorplaceholder
From: ellert@convex.UUCP
Newsgroups: sci.electronics
Subject: Re: HELP with LASRS and GRAPHICS!!!!
Message-ID: <61700003@convex>
Date: 14 Apr 88 21:52:00 GMT
References: <4333@cup.portal.com>
Lines: 41
Nf-ID: #R:cup.portal.com:-433300:convex:61700003:000:2353
Nf-From: convex.UUCP!ellert    Apr 14 16:52:00 1988


There is something called an A-O modulator (probably acoustic-optical) that
when properly driven will deflect the beam a few degrees.  The device
consists of a crystal of some presumably exotic material which is driven by
a high frequency oscillator/amplifier.  The beam is directed *through* the
crystal and logic or video signals input to the high frequency driver cause
the crystal to refract the beam differently causing it to deflect a little.

The only one I have seen used a 40 mHz (!)  driver, was physically very
small (2 or 3 cubic inches), used a LOT of power (got real hot during
operation), and was capable of modulation well into the video range,
although the deflection was a mere 7 mm @ 1 meter.  At this distance, the
beam can be moved past a hole or slit for digital modulation or across a
variable gradient filter for sorta analog output.

These are available from Meredith Instruments for $100 or so.  

There are some laser head/modulator assemblies floating around the surplus
market that were removed from large FAX equipment.  The assembly includes an
AC HV laser power supply, a 1.5 mW precision multi-stepped-capillary bore He-Ne
laser tube (current modulates better than straight bore...), intensity
feedback, and a modulator board.  All that is missing is a +/- 15 vdc power
supply to run the modulator.  Seems like both analog and digital response
was good out past 80 kHz.  I have seen these at flea markets and some
surplus catalogs for around $150.

The only really CHEAP laser modulator I am aware of (and it probably does
not work) is a polorization rotator...  Saw this at the International
Science Fair in 1971:

The beam from a high spectral purity, polarized laser is sent down the air
core of a long (6 feet) coil wound with a single layer of small wire with a
polarizing filter on the output end.  The high-current modulation signal was
applied to the coil, thereby rotating the polarization of the beam.  This
rotation caused a beam of varing intensity to exit the polarization filter
on the end.  I have not seen this actually operate, however the project did
win it's regional competition back when there was a relatively higher level
of technology demonstrated by high school students - so maybe it does work a
little.   Probably only a few percent modulation, though.

leigh   (214) 952-0598  (214) 492-5794