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Magnus Danielson wrote:
From: Dr Bruce Griffiths <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] HP 10811A/B OCXO OP/SRV manual is
onlineathparchive.com AND HP 5501B manual.
Date: Wed, 08 Nov 2006 11:25:44 +1300
Message-ID: <[EMAIL PROTECTED]>
To measure the Allan variance you need at least 2 (preferably more)
stabilised lasers and a mixer (photodiode) plus a suitable amplifier to
produce a beat signal for analysis.
The beat frequency may be as high as 100 MHz with a pair of 5501s
(frequency/wavelength accuracy of 0.1ppm) so the photodiode and
associated amplifier will need adequate bandwidth.
It seems like three 5501s, optical splitters/joiners and a fairly normal
counters should allow for a three-cornered hat and then should the Allan
variance and friends be possible to measure.
Cheers,
Magnus
Since the 5501 and similar laser heads use Zeeman splitting to produce 2
superimposed orthogonal linear polarised beams with slightly different
frequencies, polarising optics (beamsplitters, etc) will be needed to
separate the 2 orthogonally polarised beams. The frequencies of the two
orthorgonally polarised beams are symmetrically disposed about the laser
doppler gain profile peak. However the difference between the 2
frequencies (a few MHz) isn't precisely controlled and it varies from
laser head to laser head.
The laser frequency is stabilised by adjusting the cavity length so that
the 2 orthogonally polarised beams have equal power.
Bruce
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