Attila Kinali wrote:
On Sun, 28 Apr 2013 17:50:06 +1200
Bruce Griffiths<bruce.griffi...@xtra.co.nz> wrote:
Has anyone considered a laser pumped variant like:
http://tf.nist.gov/general/pdf/1009.pdf
Apart from the ECDL laser (can be assembled using readily availalble
parts) it looks fairly straightforward.
Considered, yes, tried, no. From what i've read sofar, this system
has the problem of locking the laser wavelength onto the right
absorbtion line. IIRC the linewidth of Rb in a vapor cell is a couple
of 10kHz to a few 100kHz. Using an ECDL you get a laser linewidth of
less than 1MHz easily, usally in the range of a few 100kHz and less.
Ie. the laser would need to be kept on the absorption line with a stability
of a couple of 100kHz at most. Using just a laser diode (without the
external cavity) with its linewidth of>100MHz makes it actually a
little bit easier to handle.
But the pump laser is then too noisy to allow a low noise rubidium
standard to be implemented.
With a temperature stabilised ECDL locking the laser to the D1 or D2
rubidium absorption feature whilst simultaneously stabilising the laser
beam power can easily be achieved.
But getting the laser to the right Rb absorption line and detecting whether
it's off is still not solved. Most of the papers that i've read that do
something similar use an additional vapor cell to determine the correct
position of the laser.
I'm quite sure that it could be done with a single vapor cell using
some sophisticated control loop that steers both the 6.9Ghz signal
and the laser wavelength, but i doubt it's easy. But then, i didn't
have an in depth look at this.
Attila Kinali
Bruce
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