New technique makes atomic fountains clocks more stable

March 19th, 2009 - 4:44 pm ICT by ANI  

Washington, March 19 (ANI): With the aid of a new method developed by scientists in Germany, the output frequency of the atomic fountains clocks has become more stable.

At present, Caesium fountain clocks are the most accurate clocks in the world, furnishing the second accurate to 15 places after the decimal point.

Until they reach this accuracy, caesium fountain clocks, however, need a certain measurement time.

This time has now been considerably reduced with the aid of a new method developed at the Physikalisch-Technische Bundesanstalt (PTB), which makes the output frequency of the caesium fountains more stable.

For excitation of the caesium atoms, the PTB physicists make use of a novel microwave source.

They replace the oscillating quartz by a microwave oscillator, which has been stabilized with the aid of a laser to such an extent that its noise becomes insignificant for fountain operation.

For this purpose, techniques were applied which have originally been developed for optical atomic clocks, which are regarded as the atomic clocks of the future.

Now, these previous competitors can complement one another, and the technology of the optical clock leads to a considerable improvement of the established caesium clocks.

Caesium fountains are more accurate than normal atomic caesium clocks, because in fountains, the caesium atoms are cooled down with the aid of laser beams and come ever slower.

Thus, the atoms remain together for a longer time so that the physicists have considerably more time to measure the decisive property of the caesium atoms which is required for the generation of time: their resonance frequency.

When a maximum of atoms has changed into an excited state, the frequency of the exciting signal is measured - those approximately nine billions of microwave oscillations which must elapse until exactly one second has past.

In this way, the second has been defined in the International System of Units, SI.

Realization of the second is achieved the more accurate, the finer the frequency of the microwave signal is tuned to the resonance frequency of the atoms and the lesser the microwave signal varies around the optimal value.

This noise is considerably reduced with the aid of the new technique. (ANI)

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