Andrew Back writes:

On Saturday, 8 March 2014 21:04:52 UTC, Samuel M. Goldwasser wrote:

I should note that if the color of the discharge truly looks correct,

it should lase despite the problems with keeping it lit.



However, it's hard to tell from digital photos whether this is the

case. The proper color is bright unsaturated red-orange, sometimes

refered to as "salmon" color. short of spectral analysis of the

discharge glow, comparing it with a known healthy red HeNe laser

tube would be best. IF it's too pink or weak, then it's probably

leaked.

I've been looking at a low cost spectrometer solution:

http://www.science-surplus.com/products/spectrometers

Do you know which grating might be best for this sort of task, and
perhaps also using with Ar lasers?

If the SP specs are to be believed, the tube voltage is way low, which

is another symptom. That really is the only way the tube voltage can

be low with the proper current. It's not a power supply fault.

This I don't quite get -- how can the tube drag the voltage down if
the current is correct? My guess was that the current would need to be
too high.

The VI relationship of a gas tube is highly non-linear and also depends
critically on the gases present. Add in low-excitation energy gases
like N2 and O2, and the voltage is lower at the same current. This
isn't a fixed resistor!

As far as the spectrometer, I've heard that they work well but the
resolution isn't that great. I use a Verity monochromator. It's more
of a pain to use being manual with a micrometer. But with a set of
narrow slits, it can easily small fraction of a nm.

--
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