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From: siegman@sierra.Stanford.EDU (Anthony E. Siegman)
Newsgroups: sci.electronics
Subject: Re: Looking for cheap visible red laser diodes
Keywords: laser diode red
Message-ID: <435@sierra.stanford.edu>
Date: 23 Dec 89 08:55:25 GMT
Sender: siegman@sierra.STANFORD.EDU (Anthony E. Siegman)
Reply-To: siegman@sierra.UUCP (Anthony E. Siegman)
Organization: Stanford University
Lines: 48

Commercially available visible (red) diode lasers are just coming on
the market.  They are being intensively developed by Toshiba, NEC,
Hitachi, Mitsubishi, Sony and Sharp -- all in Japan (naturally).
Toshiba is said to be the only firm making and selling production
quantities at this point.

The wavelength of these diode lasers is around 670 nm (6700
Angstroms), which is readily visible though getting pretty far down on
the red side of the sensitivity curve for the human eye.  The
wavelength of the helium-neon (He-Ne) gas laser is 633 nm (6328
Angstroms), where the eye is considerably more sensitive.  The
original pulsed ruby laser was at 694 nm (6943 Angstroms), still
further in the red.  It will probably be difficult to push diode
lasers to shorter wavelengths than around 670 nm.

Several small U.S. companies are packaging and selling these visible
diode lasers for a few hundred dollars, presumably the Toshiba models
though I don't know that for sure.  I've seen an ad for a diode and
power supply assembly from D. O.  Industries in Rochester, NY,
1-800-828-6778 or 716-359-4000.  Another source is LaserMax, Inc.,
Rochester NY, 716-328-2178.

I have one of the latter units in front of me as I write.  It costs
$295.00 complete and has the diode packaged in a hand-held cylinder
about 3/4" in diameter and 2-1/2" long with a built-in collimating
lens for the output beam.  Power output is 4 mW, and it looks plenty
bright.  Beam collimation is reasonably good -- you can point the beam
into a tree several hundred feet away at night and readily see the
spot reflecting off leaves and twigs.  The kit includes a small
battery pack (4 AA batteries -- probably an hour or two operating
time) which will drive the diode head directly and also a 110 VAC to 6
VDC power supply.  Operating current is 75 to 85 mA.  Spec sheet life
is >50,000 hours at 3 mW output, >5,000 hours at 4.9 mW output.

Whether you can buy diodes direct from Toshiba I don't know.  I'd
expect to see packaged units from Edmund Scientific very soon.

In general, GaAs diode lasers operating at around 800 to 880 nm in the
near IR can be operated either cw at milliwatt power levels, or
operated pulsed with 1 to 10 nanosecond pulses, low duty cycle, with 1
to 10 Watt peak powers and about the same average powers.
Life-limiting mechanisms are partly overheating, which depends mostly
on the average power, not the peak power; and partly facet damage and
internal diffusion, which do depend on peak current and peak power.
Whether these particular visible lasers, which use a GaAlP
(gallium-aluminum-phosphide) alloy can be operated in the high-power,
low-duty-cyle pulsed mode I don't know.  It's not mentioned in the
spec sheet.