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

[Magnus Danielson]

Hi Leo,

The physical package is wrapped such that essentially no ambient light 
comes in, the other design requirements drive the design that way 
anyway, both magnetic shielding and RF cavity, so I consider there being 
no need to do additional dim outs.

You do not want to dim the photodetector itself fromt he light through 
rubidium. You already face a signal to noise problem there that will 
affect the stability.

The Varnier and Audoin "The Quantum Physics of Atomic Frequency 
Standards" Vol 1 and 2 is very relevant too. These books are somewhat 
older, but great in depth reference. The Riley Rubidium Frequency 
Standard Primer is more modern, gives great orientation, but for some 
aspects do not go into more depth than necessary, which is fine, it is 
an excellent starting point that cover most issues, so read that first, 
and then dwell into Varnier and Audoin.

Cheers,
Magnus

On 2023-06-08 18:45, Leo Ahluwalia via time-nuts wrote:
> Hi Magnus, I'll definitely have to take a look at the resources Tom, zfe,
> and Andy sent my way. To my theoretical knowledge, the attenuation of the
> photo-detector is a possibility - to avoid having to dim out the room where
> the apparatus is contained - and I was wondering if you or anyone else had
> experience working with something of that nature. I appreciate the advice
> on the setup, it definitely cleared up some things for me.
>
> - Leo
>
> On Wed, Jun 7, 2023 at 9:27 PM Magnus Danielson via time-nuts <
> time-nuts at lists.febo.com> wrote:
>
>> Hi Leo,
>>
>> So, the setup is very straight forward. You put the Rb-lamp, the filter,
>> the Rb resonance cell all lined up in a straight path and at the far end
>> of that you have a photo-detector. The resonance cell you want to keep
>> magnetically shielded, which is typically done by one or more (I have
>> clocks with 3) layers of mu-metal. You have a coil, called C-field coil,
>> through which a DC current creates a magnetic field that separates the 5
>> Rb resonances so that only the (1,0)->(2,0) absorption occurs, which is
>> detected by a thad lower intensity of the pump light.
>>
>> Look at Tom's email and I strongly suggest you get "Rubidium Frequency
>> Standard Primer" of William J. Riley which has a lot of info in it
>> covering a lot of the things that goes into it. This includes a lot of
>> photo of the actual inner parts of the rubidium clocks. There is more
>> material to gather, but already that book will answer a lot of things
>> for you and summarizes a lot of stuff in a very condensed and straight
>> forward way.
>>
>> Cheers,
>> Magnus
>>
>> On 2023-06-08 00:38, Leo Ahluwalia via time-nuts wrote:
>>> I appreciate all of the help so far, and assuming the procurement of a
>>> rubidium vapour cell and rubidium lamp (and of course all the other
>>> components), I was wondering how exactly the optical pumping setup should
>>> be achieved (to make sure all the components are "hooked up" so to
>> speak),
>>> and whether there was already a standard way of achieving it along with
>> the
>>> installation of the magnetic shielding?
>>>
>>> - Leo
>>>
>>> On Wed, Jun 7, 2023 at 6:27 PM Bruce Griffiths via time-nuts <
>>> time-nuts at lists.febo.com> wrote:
>>>
>>>> That just leaves the Rubidium lamp.
>>>> An ECDL (external cavity diode laser) locked to the appropriate Rubidium
>>>> transition is much easier to build. There are several ECDL designs in
>> the
>>>> literature. Mostly these are Littrow designs. A Cateye resonator design
>> is
>>>> another option. All the components required are readily availble.
>>>> VCSEL's should be avoided as those without polarisation mode
>> stabilisation
>>>> gratings on the output face randomly mode hop between a pair or
>>>> orthogonally polarised modes.
>>>> A well designed but relatively simple ECDL can have a much narrower line
>>>> width than a typical DFB laser.
>>>>
>>>> Bruce
>>>>> On 08/06/2023 06:37 NZST djl via time-nuts <time-nuts at lists.febo.com>
>>>> wrote:
>>>>> The Rb capsules are available on ebay, eg:  124012486501
>>>>> the classblowing part is done?
>>>>>
>>>>> On 2023-06-07 07:50, Richard (Rick) Karlquist via time-nuts wrote:
>>>>>> On 6/7/2023 5:03 AM, Stephen C. Menasian via time-nuts wrote:
>>>>>>
>>>>>>> 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;
>>>>>> At HP we had really skilled glass blowers, with specific experience in
>>>>>> making Rb glassware.  We had to use an exotic grade of glass that was
>>>>>> only one step removed from fused quartz.  It had a part number that I
>>>>>> don't remember.  Very difficult to work with.
>>>>>>
>>>>>> The Rb lamp (one of three pieces of glassware) is very tricky to work
>>>>>> with.  We used a resonant coil driven at 95 MHz at several watts.
>>>>>> The trick is to "strike" the plasma and make the lamp light up;
>>>>>> you can at least see visible light when that happens. I spent a
>>>>>> lot of time fooling with it.  We never got it to work as
>>>>>> well as the 5065 lamp.
>>>>>>
>>>>>> BTW, one of the Rb isotopes is slightly radioactive.  Might be
>>>>>> hard to get as a hobbyist due to regulations.  The physicist I
>>>>>> sat next to had a tank of it illegally stored in his cubicle.
>>>>>>
>>>>>> Rick
>>>>>> N6RK
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