[time-nuts] homebrew maser

John Miles jmiles at pop.net
Tue Aug 31 23:49:19 UTC 2010

That's a great article.  It almost makes the job seem doable.

It is going to be expensive, though.  If someone can build a working maser
for less than $10K in materials and bespoke fabrication services alone, I'll
be impressed.  An obvious question is, what's the so-called "minimum viable
product" that can actually produce a population inversion in a cavity and
demonstrate maser action?  Do you need any magnetic shielding at all, beyond
a couple of Helmholtz coils?  Maybe not.  Do you need to coat the bulb at
all if you don't care about line width?  Maybe not.  How exotic does the
collimator need to be if you don't care much about service life?  Probably
not very.  You definitely don't need a multilayer vacuum system.  What
corners can be cut to get a rough prototype running?

Control electronics is trivial, and not even worth thinking about until the
physical details are nailed down.

Once you start talking about cutting corners just to get a maser up and
running, though, there's another obvious question worth considering: what
about starting with an ammonia maser?  This was the first molecular
oscillator.  Experience optimizing the (numerous) operating parameters in an
NH3 maser would no doubt be helpful in later work with an H maser.

Ammonia molecules have a dipole moment and can be state-selected
electrostatically.  There is no need for either a dissociator or a storage
bulb, just a basic electrostatic lens and cavity in a vacuum.  Townes's
original 1954 paper makes no mention of magnetic shielding.  But at 24 GHz a
high-Q cavity is small and manageable, so if you do have to enclose it in
mu-metal it's not going to cost a fortune.

Further, with stabilities in the 1E-12 range, a 5065A-class rubidium
standard or a well-optimized GPS clock can be used as a reference for
tweaking and debugging an NH3 maser.  If you do manage to build a hydrogen
maser, OTOH, you are going to need to build at least two of them to get any
idea where your performance floor is.

Just one possible thought...

-- john, KE5FX

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Bruce Griffiths
> Sent: Tuesday, August 31, 2010 1:23 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] homebrew maser
> PTFE wall storage bulb wall coatings haven't been used for some decades,
> FEP (or the Russian fluoropolymer ) is better in that a smoother coat is
> achievable see:
> http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&
> AD=ADA509340
> <http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf
> &AD=ADA509340>
> A sual hexapole state selector is probably a little more effective than
> the cruder method used in the Russian masers.
> Bruce
> Mark Sims wrote:
> > Same general idea,  but an image intensifier plate would
> probably not work well.  They are usually thinner and are cut at
> a bias so the electrons ricochet along its length.  You might be
> able to mount one so that it cancels the bias angle.
> >
> > They are made by stretching a bundle of hollow glass tubes that
> have been filled with solid glass rods of a different
> composition.  The original bundle can be very large (like over a
> meter) and is shrunk down to like 100 fibers per millimeter.  It
> is then sliced and polished.  Often the slices (or the pulled
> bundles) are joined into a bigger plate.   Then the inner solid
> glass is dissolved out with a strong alkali. The hollow tubes are
> coated with a photoelectric material.
> > The image from the tube is inverted using a "twister"...  a
> coherent fiber optic rod that has a 180 degree twist.
> >
> > ---------------
> > Do you know if the collimator is made from an uncoated
> microchannel plate?
> > If so, an old, broken Gen II image intensifier might be a viable source.
> >
> >
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