[time-nuts] LED instead of discharge lamp for Rb vapor cell standards

Attila Kinali attila at kinali.ch
Wed Feb 21 12:49:28 EST 2018


Has anyone ever tried using a LED instead of a discharge lamp for Rb standards?
There are quite a few and very cheap 780nm IR LEDs available. They usually
have a line width in the order of 20nm to 50nm (FWHM). This means that they
still need the Rb85 filter, but they would not produce all those spectral lines
that the discharge lamp has, thus one could get rid of the (not so cheap)
optical filter that Corby uses for the super-5065. 

The one thing I am not sure about is the filter efficiency of Rb85.
Because now the light isn't two discrete lines from the Rb87 lamb
of which one needs to be masked, but a continuous and wide spectrum.
So the Rb85 "notch" filter might not get rid of all the unwanted light
and some of this might depopulate the excited state of the Rb87
that are in the RF cavity.

As a side-effect, you also get easier regulation of the light intensity
of the LED, thus potentially less instability due to light-shift variation.
Beside the LED operation being much simpler than that of a discharge lamp
and overall less heat dissipation.

			Attila Kinali

It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson

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