[time-nuts] New frequency standard, Mercury better than Cesium?

[Rob Kimberley]

All,

Here is some more information on the work being done at UK's National 
Physical Laboratory on Optical Frequency Standards, and their work on using 
Strontium and Ytterbium.

http://www.npl.co.uk/optical_frequency_standards/introduction/index.html

Regards

Rob Kimberley




----- Original Message ----- 
From: "Magnus Danielson" <cfmd at bredband.net>
To: <time-nuts at febo.com>; <hmurray at suespammers.org>
Sent: Monday, July 17, 2006 9:08 AM
Subject: Re: [time-nuts] New frequency standard, Mercury better than Cesium?


> From: Hal Murray <hmurray at suespammers.org>
> Subject: Re: [time-nuts] New frequency standard, Mercury better than 
> Cesium?
> Date: Sun, 16 Jul 2006 10:28:19 -0700
> Message-ID: <20060716172820.435B3BDF0 at ip-64-139-1-69.sjc.megapath.net>
>
>> >From the horses mouth:
>>
>>   http://www.nist.gov/public_affairs/releases/mercury_atomic_clock.htm
>>
>>
>> This brings up a question I've been meaning to ask for a while.
>>
>> How do you tell how good your best clock is?  I can figure out how good a
>> not-great clock is by comparing it to a better one.  But what if there 
>> isn't
>> a better one?
>
> There are basically two methods that have been in use:
>
> 1) Build two clocks and compare them against each other. This is what 
> Ramsey
>   et al did for the hydrogen masers. Their phase-noise sould be about 
> equalent
>   so you can put down both clocks for the 1/sqrt(2) of the measured phase
>   noise (they contribute the same amount of noise energy with the same
>   distribution in this assumption).
>
> 2) Compare three clocks, all of low phase noise. Make three pairs of
>   measurements for clocks 1-2, 1-3 and 2-3. The noise contribution of each
>   clock into each measuremnts allow for cancelation and the phase-noise of
>   all three clocks may be found.
>
> As an alternative to method 2 you may have a clock with know phase noise, 
> but
> then measure your new clock against it and they subtract out the phase 
> noise of
> your known clock. Whenever you compare the phase-noise of a better clock 
> with
> known clocks, you rarely want to have a phase-noise more than a decade 
> worse
> then the clock you are going to measure, since you will run into the 
> precission
> of the decimals and that takes averaging time.
>
> They can often quite accurately predict the phase noise they get. They 
> have a
> fair idea of the various sources of errors and it is this understanding 
> which
> have led them towards this type of sources. Infact, at one time Thallium 
> was
> competing with Cesium to become the standard and it was judged to be more 
> than
> 2 times more precise, but it was ten judged that microwave design at 24 
> GHz was
> more delicate (and thus harder to stablize and repeat) then down at 9.2 
> GHz so
> it was the wavebreaker then.
>
> I've seen this work going on for a few years now.
>
> Hmm. With ultraviolet lasers you should be able to get the ultimate suntan 
> in
> no time. ZAP! :P
>
> Cheers,
> Magnus - yes, I am on vacation, but keeps track of fellow time-nuts
>
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