From: wellison@kuhub.cc.ukans.edu
Newsgroups: sci.electronics
Subject: Re: Lasers/collimated light in RGB?
Date: 30 Dec 92 19:15:33 GMT
Organization: University of Kansas Academic Computing Services


<My first posting was truncated.  Here's how it should have read.
<
<In nightclubs I have recently seen light effects which apparently
<use bright red, green, and blue lasers which are modulated with 
<mirrors (I think) to do interesting things like project color 
<images on a wall.  The red could be a simple He-Ne laser, but what 
<about the green and the blue?  I know these light sources can be 
<made with expensive and sophisticated lasers, but how could this 
<be done as simply and inexpensively as possible?  Is it possible 
<that these really weren't "lasers" and were instead some sort of 
<collimated and color filtered bright light sources? 
<
<I'm also curious how the light sources are modulated to get fairly
<decent resolution at high refresh rates.  Just guessing, in one 
<setup I would say the resolution was at least 100 x 100 on the wall,
<maybe a lot better, with a refresh of around 60 Hz.  This may be 
<implemented with a set of really fast stepper moters, but I'm not 
<sure.  Anyone know how these tricks are done?  Thanks in advance.
<
<John Lange (jlange@zippy.radian.com)

Actually, there are several ways that the RBG light system works. The most cost
effective would be to use a high powered HeNe (around 20mW) and a multi-lined
Argon laser which produces blue-green (488Nm-514Nm) at the same time. By using
a diffraction grating in front of the argon laser and shifting it's position
relative to the beam axis, the blue line and green line can be separated. Now
you have red (the HeNe), blue and green beams. Next, color modulation is done
by either using AOM's (Acustical Optical Modulators which cost big bucks !) or
a 'Z' axis galvo mirror in the beam paths to select the desired color. The
graphics are done by a set of X-Y axis scanning mirrors. These (along with the
'Z' axis mirror) are basically precision stepping motors (or called 'GALVOS' in
the trade). Scan speed is around 300Hz. The picture is drawn by point vectoring
the laser beams where you want them. In other words, you draw a line from point
to point, then another line and so forth. At some point, you will have a
retrace line, which is unwanted, so the 'Z' galvo acts a a blanking mirror for
the retrace. Commercial shows use a PC to generate the patterns and drive the
scanning circuitry, however, some use audio tape with pre-programmed frames,
which drives the scanners. Each part of the picture is a frame. Each frame has
to be drawn and sent to the scanners. The speed at which the frames are sent to
the scanners determines how the picture will move.

A more expensive method which is used at rock concerts and outdoor displays
uses a 'White Line' laser. This type of laser is a Krypton gas laser (no, not
superman krypton either ;-). These lasers produce the three basic colors (RGB)
at once and they are tuned to the desired color by a etalon prism. But the cost
$35,000 and up ! Some shows use a meduim powered multi-line argon (5 watts) for
blue-green and a meduim powered krypton laser (1 watt) for yellow through red.
Just the cost of those two lasers cost as much as a three bedroom house and
that's not counting the scanning equipment to go with them !

Fortunatly, laser shows for the night club scene and the hobbiest can be built
anywhere from $500 to several thousand dollars. The hobbiest can build a nice
little show of his own using a set of galvantic scanners (these are like 8 ohm
voice coils from a speaker and cost $95 a pair with the dichoric mirrors), a
3mW HeNe laser and power supply (about $250), and an amplifier/oscillator to
drive the scanners. The oscillator produces lissajous and quadratures or the
amp can be coupled to the right and left speaker outputs of your stereo to move
the laser in beat with the music. Several companies sell these parts and
complete shows as well. They are:

MWK Indutries
197 Lewis Court
Corona, CA. 91720
1-800-356-7714
1-714-278-0563

Meredith Instruments
P.O. Box 1724
Glendale, AZ 85301
1-800-722-0392
1-602-934-9387

Design Images
P.O. Box 292125
Lewisville, TX 75029
1-221-9711

They sell shows ranging from $325 complete to >$7,000. So the wallet decides
here ;-)

-=-= Wes =-=-