[time-nuts] Cheap Rubidium (heatpipe cooling for)

[Magnus Danielson]

Bruce Griffiths wrote:
> Probably the temperature fluctuations of the absorption cell is more 
> significant than that of the lamp itself.

The lamp itself shifts intensity sligthly, but the three most sensitive 
points to temperature and temperature shifts is the resonator cavity 
(pulls the frequency as it detunes), buffert gas shift change with 
temperature and this balance the wall-shift so shift in temperature 
change the buffer-gas/wall shift balance and shift in temperature will 
cause the OCXO to shift and that needs to be canceled in the loop.

The main effect of the lamp temperature is to shift S/N.

All according to my limited knowledge in the field.

> The effects to consider are:
> 
> 1) The effect of temperature fluctuations of the electronics.
> Probably dominated by the short term temperature fluctuations of the 
> internal crystal oscillator.

The magnetic field applied could also vary. To the best of my knowledge, 
I do not know of a way to servo the magnetic field in the fashion it is 
done for cesium beams. This servo is part of the modernisation that made 
cesiums much more stable.

> 2) The effect of temperature fluctuations of the Rubidium lamp and 
> associated optical filters.

Mainly shift in intensity and also the temperature widening of the 
relevant wavelength. Likewise with the rubidium filter cell absorbing 
the unwanted wavelength.

> 3) The effect of temperature fluctuations on the Rubidium absorption 
> cell hyperfine transition frequency.

Buffert-gas mix vs. wall-shift balance depend on temperature. At some 
temperature the buffert-gas completely cancels the wall-shift. We can 
expect the gas-mixture to shift over time and thus the 
shift-compensation for a certain temperature, so there is a wear 
mechanism in play.

4) The effect of temperature fluctionations on the Rubidium frequency 
resonator.

Resonator cavity frequency shifts with temperature as material expand 
(on rising temperature). The Q of the resonator plays a role in the 
amount of frequency pulling.

These effects is well covered in the literature.

Cheers,
Magnus