writes:

On Wednesday, September 11, 2013 3:57:18 PM UTC-4, Samuel M. Goldwasser wrote:
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. ;-)
Hi Sam, Thanks for the response. You're talking about sending the
laser into a F-P and looking at the output? A flat mirror F-P
(Etalon), a confocal curved mirror F-P, or something in between?

Generally, a confocal FP is best since it greatly simplifies alignment.

For the HeNe, the mirror Radius of Curvature (RoC) of both mirrors needs
to be less than about 50 mm so that the Free Spectral Range (FSR, or
mode spacing of the FP) is larger than the gain bandwidth of the
HeNe red transition.

One of the FP mirrors is then mounted on a piezo transducer (PZT) and
the FP is scanned rather than the laser. The PZT can be the beeper
element from a digital gizmo or less than $2 from Digikey.

More info at: http://www.repairfaq.org/sam/laserlia.htm#liasfpi

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