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

[Bruce Griffiths]

Thorlabs make Rubidium 87 absorption cells.
They recommend borosilicate glass rather than fused silica.
Borosilicate glass is more resistant to chemical attack by alkali metals than fuse quartz.

Thorlabs also make custom absorption cells but the shipping overseas is very expensive due to the 49 billion year half-life of Rb87.
The Australians (https://findanexpert.unimelb.edu.au/scholarlywork/315753-linewidths-below-100-khz-with-external-cavity-diode-lasers) roll their own ECDLs for Rubidium absorption line locking.

Bruce
 
> On 09/06/2023 04:38 NZST Leo Ahluwalia via time-nuts <time-nuts at lists.febo.com> wrote:
> 
>  
> Hi Stephen, I appreciate the advice, and while glass-blowing isn't
> something I've had much experience with, making the glass package
> definitely sounds like a fun challenge.
> 
> Thanks, Leo
> 
> On Wed, Jun 7, 2023 at 8:23 AM Stephen C. Menasian via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
> > 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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