NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/sci/physics/22378

Internet Message Format | 1993-01-09 | 4.4 KB

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From: [e-mail] (Steve Warner)
Newsgroups: sci.physics
Subject: Re: Lasers/collimated light in RGB?
References: <[e-mail]>
Message-ID: <[e-mail]>
Date: 8 Jan 93 09:20:09 CST
Organization: Not an Organization
Lines: 62

A
=>First, is it at all possible to do an outdoor laser show during the day,
=>perhaps using a huge thin smoke filled enclosure with a clear front face?
=>If it is possible, how much extra power would be needed from the laser(s)?
==*  John, generally the large shows you see, in stadiums and such, use
lasers rated in watts. These shows usually take place at night, to promote
the "laser beam shaft" effect. These large multiwatt lasers are "serious"
machines, which do require water cooling, are quite hazardous, and need
special permits from the CDRH to operate. (Center for Devices and
Radiological Health administration). Daytime conditions (especially bright
sunlight) will wash out the "beam shaft" effect, But you will be able to see
a scanned "image" drawn with the laser...especially if the beam is a visible
blue/green type. Your eyes are most sensitive to the blue/green spectrum.

=>Is it possible to use some semi-opaque material such as a thin cloth and
=>put the laser(s) behind the projection to make it more visible during
=>the day?
==*  I've seen translucent screens used successfully in both indoor and
outdoor laser image generation.

=> Next, beam dispersion is apparently around 1mrad for HeNe and
=>Argon lasers.  This is of course very slow dispersion, but if one wanted
=>to transmit the beam a long distance and retain the entire cross-section,
=>can collimating lenses correct for the problem or do they make the
=>problem worse?
==* Beam dispersion is a function of cavity length. Short cavity lasers tend
to loose their coherency more quickly as the beam travels from the laser
source,...and long cavity lasers tend to remain tightly packed and coherent
over longer distances. Collimation optics help tremendously...normally a
simple telescope type of arrangement. Be sure to collimate the beam BEFORE
you run it into the scanners tho, or the refraction of the optics will deaden
(clip) your scan widths. To give an example of the effect of a typical
collimator: a "long tube" 1.2mR HeNe beam will disperse to a width of about
10 inches at about 900 feet. The same beam when collimated using a standard
telescope will expand to only 2 inches at 900 ft. (info taken from The Laser
Cookbook, Gordon McComb, Tab Books, 1987 pg 127)

    I've been into the laser hobby for many years now and have found many
sources of info, parts and materials in my travels. The "surplus" market is
ablaze with goodies for the workshop tinkerer. I was able to pick up a broken
Argon laser head (American 60) and regassed it with fresh argon. Total cost
on the head was under $500 and its proven to be a beautiful 1/2 watt, air
cooled, multimode (multiple wavelength) argon ion laser. A real work horse.
In a similar sense, all of my HeNe, diode, and solid state
(flashlamp/crystal) devices have all been made from parts available on the
surplus market. One of the best sources has been Chad Anderson of Meredith
Instruments (5035 North 55th Ave, Glendale AZ.  84301 [phone]).
Also if your interested in "Red" beams, don't forget to check out surplus bar
code scanning machines available from many suppliers. I've seen 2-3mw lasers
go for as little as $45. High power "red" (670nm) diode lasers are also
available now. I just recently built a 10mw x/y scanner using the Toshiba
TOLD9215 diode (Unicorn Electronics) which fits in the palm of your hand.
(laser, power supply, scanners and electronics) Altho a tad more expensive
than HeNe, its performance is outstanding for its size. Brightness can be
compared to that of a 5-6mw HeNe.
    Wall plug efficiency of "most" gas lasers is pretty dismal. Off hand I'd
say Less than 1-2% in most cases.
    In reference to laser image design, the best system I've seen is the
Pangolin Laser Software for the Amiga computer. Their top of the line
generators are capable of 3d animation...very nice stuff...as well it should
be. Cost of their LD400 system is 8 grand. I do have a demonstration VHS tape
of this system...if you'd care to view it.