[Boatanchors] RE: 2X2 question

[J. Forster]

Mark Foltarz wrote:

> Yes, my mistake on the mercury in the 2X2. It is a hard vacuum tube.
>
> For some reason I was fixated on the 866 and the thought that the 2X2 was an
> 866 jr.  I had four of those in my Drake powers upply for my ART-13.
>
> But in regards to the early HeNe laser failures, I think that was most likely
> bad seals where the optics are glued to the main tube body as opposed to
> diffusion through glass.
>
> Thoughts?
> de KA4JVY
> Mark

Lasers fail because of He diffusion through glass. Period. Consider the
following:

1.  I have a number of HP 5501A lasers. (They are used in the HP Interferometer
systems) After a number of years (say 10) the laser power falls to unusable
levels. These are not $29 supermarket bar code scanning lasers, but $5000+ Zeeman
split, frequency stabilized units. HP agrees it's the He leaking through the
glass

2.  Liconix makes HeCd lasers. They have a He reservoir to replenish the He lost
to the tube by sputtering of the Cd. If the laser is NOT used for a couple of
years, it fails due to excess He leaking INTO the tube from the high pressure
reservoir.

3.  I was using an EMR photo multiplier in a He atmosphere. It failed in about a
month, due to He leakage into the tube.

4.  When I was doing cryogenic research, we has special glass dewers for liquid
He. Someone forgot to purge the He out of the dewer one night and ruined it.

Helium diffuses through glass. PERIOD.

-John