Date: Fri, 08 Feb 2002 09:09:08 -0500

Author: Jim Stango

Subject: Re: Laser Purchase


The Metrologic 1 milli Watt Helium Neon Lasers sold by Cenco are also a
nice laser to use for interference and diffraction experiments. With ours,
we removed the threaded optical mounts and replaced them with adhesive
magnetic strips so that we can easily attach and adjust slits, gratings,
and apertures. The "Red" lasers work well in a dark classrooms and/or
small auditoriums, but with large auditoriums (or wide slit separations) you
may want to use .5 to 1 milli Watt
"Green" Helium Neon lasers. They are usually much more expensive, but
since our eyes are more sensitive to greens then reds, interference and
diffraction patterns are much easier to see. I would try to stay away from
the Metrologic "Green" Diode Laser Model ML815. Ours constantly mode
shifts, which can be instructive in itself, but for displaying interference
and diffraction effects it is useless.

Jim Stango
University of Pittsburgh

- Original Message -----
From: "Curry, Robert"
Sent: Thursday, February 07, 2002 6:02 PM
Subject: Re: Laser Purchase

> The Uniphase He-Ne lasers (sold by Edmund) with the "random" polarization
allow you to
> demonstrate an interesting property. Turn one on, put a polaroid analyzer
in the beam, and
> rotate the analyzer until the beam is extinguished. In a moment the beam
will reappear. In
> another moment it will disappear again. Rotate the polaroid 45 degrees
and the beam will
> remain constant (nearly).
> What happens is this: As the laser tube warms up, the resonant cavity
expands, producing a
> sequence of resonant modes, each of which is polarized perpendicularly to
the ones before
> and after it. By rotating the polarizer until you get complete
extinction, you have put the optical
> slits parallel to one set of modes and perpendicular to the other.
> Bob Curry