[time-nuts] CCD lock detection (was: DIY Physics Article)

Chris Albertson albertson.chris at gmail.com
Wed Feb 22 18:57:01 UTC 2012

The trend with Rb clocks is to try and make then smaller and cheaper.
If all you need to do is detect the amount of light a one-pixel sensor
is enough.  If you divide the sensor into multiple pixels you just get
more noise because fewer photons fall on each pixel.   So a
photo-transisor is ideal as a detector.   Also another big problem
with CCDs is that you have to shift the charged pixels out to an
amplifier one pixel at a time so there is a small delay, the
photo-transistor outputs the light level without delay and the
associated shifter complexity.  And in the end what do you do with all
the pixels other then take an average?

I think the next generation of Rb physics packages will use a laser as
the light source and have the laser, Rb cell and detector all in one
glass envelope.  I've seen one like this that is just tiny.  But as I
recall there was a problem using a laser, something about noise


Chris Albertson
Redondo Beach, California

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