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" <[EMAIL PROTECTED]> To: <[email protected]>; <[EMAIL PROTECTED]> Sent: Monday, July 17, 2006 9:08 AM Subject: Re: [time-nuts] New frequency standard, Mercury better than Cesium? > From: Hal Murray <[EMAIL PROTECTED]> > Subject: Re: [time-nuts] New frequency standard, Mercury better than > Cesium? > Date: Sun, 16 Jul 2006 10:28:19 -0700 > Message-ID: <[EMAIL PROTECTED]> > >> >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 > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
