writes:

On Tuesday, September 10, 2013 5:04:12 PM UTC-4, Samuel M. Goldwasser wrote:
writes:



On Tuesday, September 10, 2013 3:02:50 PM UTC-4, wrote:

On Tuesday, September 10, 2013 12:58:55 PM UTC-4, tm wrote:



snip previous stuff


Thanks all. I'll pop it open and hook in a rocker switch or something like that (when no students are around, of course). Maybe I'll get lucky and the tube will still work. Otherwise, I'll talk to some friends in labs about a Helium soak.

Well if that doesn't work. What's a HeNe do, that you can't do with a red diode laser? ~$10 or so.

Actually quite a lot.

Hi Sam, What kind of things? We sell both a HeNe and a diode laser with our interferometery apparatus.
http://teachspin.com/instruments/moderni/index.shtml

The HeNe has a fixed wavelength.... and as it warms up you can watch the coherence length 'swish' around as the different longitudinal modes cross over the gain curve. But that seems like a bit of an esoteric difference for the 'normal' high school laser application.

What else do you have in mind?

There's a lot one can do with respect to the longitudinal modes, though
perhaps that is a bit of a stretch for an intro to lasers in high school.

But one can do some nice interferometry experiments with not much additional
equipment.

In fact, I see you your Web site that you do some of these things.

A Fabry-Perot with a common random polarized HeNe laser is a work of art. ;-)

The beam quality is also a lot better than most diode lasers (divergence,
beam profile).

With some you can put another mirror in front or in back of the laser
(if accessible) and get 1 or more of the other HeNe wavelengths.

I can go on and on.....

Contact me directly via repairfaq.org if you'd like.
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George H.

If it is less than about 30 years old, the tube is hard-sealed and
doesn't really leak. An ML855 could be function like new

Bypasss or replace the switch and see what happens.

Just be careful of the line voltage and high voltage inside!