[time-nuts] Re: Creating a D.I.Y Rubidium Atomic Clock

[Stephen C. Menasian]

Leo,

This is a complex, but interesting, project. The electronics/microwave
part of the project is fairly straightforward and is best left for later
phases of the project. The interesting part of the project is the
"physics" package, which I refer to as "optical pumping". My experience
in this area is a bit dated (5-6 decades ago), when my undergraduate and
PhD work was centered on optical pumping of Rb, Na and Cs atoms as well as
H2+ and Hg+ ions. A lot has changed since then; in particular, many
refinements have been made to create practical miniaturized Rb based
systems suitable for commercial time standards; I am not current on these
changes.

Your first task would be to establish and demonstrate optical pumping of
Rb87 atoms. For this, you would need, at a miniumum:

1) some pure Rb87
2) a glass blowing setup (and some skill)
3) A selection of inert gasses (at least including Ar)
4) Light source (Rb discharge was used then with a circular polarizer;
   intensity pumping via Rb89 (I believe) is often used now.
   Infrared lasers look very interesting to me.
5) A low noise light detector (I used photomultipliers - many more modern
   solid state possibilities exist now.
6) a uniform magnetic field (Helmholtz coils or solenoid) and magnetic
   shielding.
7) A means of controlling cell temperature (Rb vapor pressure)
8) A bit of electronics, including RF power for the lamp. Note that a
   noisy lamp discharge will mask the desired signal.

You should start with the Zeeman transitions, which are much easier to
observe and don't require microwave hardware. If you can't see a Zeeman
transition, there is no hope for the hyperfine transition. Getting
collisional disorientation down to a low enough level might involve
experimentation with various buffer gas formulations and pressures and
cell wall coatings (we used a very thin teflon film).

If you get to the point where you can see the Zeeman transitions, you
will have accomplished and learned a lot. With a little more effort, you
should be able to see the hyperfine transition.

Good Luck!!!

Stephen



 

On Tue, 6 Jun 2023 15:25:47 -0400
Leo Ahluwalia via time-nuts <time-nuts at lists.febo.com> wrote:

> Hello, my name is Leo, and I was wondering about the feasibility of
> creating a simple rubidium atomic clock at home, and good places to
> source parts for this sort of project. I was also wondering what
> instruments and specialized knowledge would be required depending on
> how pre-built the parts are, for example, the prerequisite knowledge
> for creating PLL(s) for both frequency division to provide an output
> and also to modulate the input of the microwave oscillator. Any good
> resources or PDFs would be greatly appreciated, as I am very new to
> frequency analysis and phase manipulation in general. I was also hoping
> to keep the cost of the project soft-line below 500$, though that would
> be assuming a decent level of precision and already possessing basic
> equipment (oscilloscope, multimeter, etc…). Safety is also a major
> concern, as I know while the intensity of the EM waves involved is low,
> the power source may or may not be. This is all of course assuming a
> basic design, where my assumption is that it will involve the
> microwaves being shot at a rubidium vapor cell which is directed
> towards a photodetector. This would then be connected up to the PLL and
> circuitry to both provide a stable standard while also modulating the
> microwave oscillator to offset any external environmental factors. I
> don't have a clear vision of what would truly be the best design for
> both simplicity and cost, though this is what I've found to be a common
> design in what I've looked at online.
> 
> 
> Thanks, Leo
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