Atomic clock

an atomic clock is a clock, whose clock pulse (usually a microwave signal) with atomic Schwingungszuständen is adjusted. Since the frequency of such oscillations is constant and can be determined very exactly, atomic clocks are the so far most exact built clocks. From the measured values of over 260 atomic clockson over 60 institutes distributed world-wide „the office international of the Poids puts et Mesures “ (BIPM) into of Paris (France) „the international atomic time “(TA) as a reference time firmly.

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function mode of oneAtomic clock

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As atomic transition frequently the hyperfine structure - transition F =4, m F =0 → F =3, m F =0 2 S of the 1/2 - initial state 133 cesium becomes - atom uses. This transition has a frequency of 9,192631770 GHz. 1967 became the SI-UNIT second overthis value fixed.

Atomic clock

so long the temperature of the cesium is not extremely low (in the order of magnitude 1 mK), is about equivalent occupied both conditions. In order to be able to measure the transition, one of the conditions must be selected. That takes place either by means of the fact that one an atomic beamby a strong, inhomogenous magnetic field sends, or by optical pumping with laser light.

The second main part of an atomic clock is a microwave cavity, in which transitions between the two conditions can take place. After the reciprocal effect with the microwave field occupation is finally measured at the beginning of out-selected condition.If the frequency of the microwave cavity agrees with the frequency of the transition, one receives a signal maximum.

In newer atomic clocks one works with slower cesium - atoms, in order to increase the accuracy. In „the cesium Fontäne “cesium atoms are first strongly cooled down, so that them only abouta centimeter per second are fast. (In the thermal atomic beam there is about 100 meters per second.) the slow atoms are accelerated then with a laser upward and go through a ballistic flight path (therefore the expression cesium Fontäne), thereby the effective reciprocal effect duration of the atoms can with the irradiated microwaves to be extended, which permits a more accurate frequency regulation. The course uncertainty of a conventional atomic clock amounts to about 1·10 - for 14 (1 second of deviation in 3 million years), a cesium Fontäne however is appropriate with approximately 1·10 - 15 (one second of deviation in 30 million years).

Beside cesiumalso rubidium, hydrogen and other atoms or molecules for atomic clocks are used. In order to achieve larger accuracies, what is worthwhile, in order to be able to accomplish physical experiments more exactly, at present experiments with elements are made, which have suitable transitions with optical wavelengths. Thereby one reachesFrequencies of hundred Tera cycles per second in place of the conventional 9 GHz. In these experiments individual ions in Paul case are stored and a laser is stabilized on a narrow-band transition (usually a quadrupole - or octupole transition). The technical challenge thereby is it, the high-stableTo down-divide laser frequency on electronically measurable frequencies. For this at the institute for Max-Planck for quantum optics a procedure was developed (frequency comb).

Another line of development beside the highly precise clocks pursues the building of more inexpensive, smaller, lighter and more energy-saving clocks, z. B. for the employment in satellites, rockets or drones. Satellite navigation systems such as government inspection department, GLONASS or (in the future) Galileo use atomic clocks in their satellites, in order to increase by their highly exact time the positioning accuracy. In the year 2003 succeeded in building a rubidium atomic clock only the volume of 40 cm 3 takes and an achievementfrom a Watt uses. It reaches a course uncertainty of approx. 3·10 - 12. That corresponds to a deviation from one second in 10,000 years, and thus the clock is clearly more inaccurately than the large stationary atomic clocks, but substantially more exact than a quartz clock. (DetailsQuartz clocks have a deviation from one second in one month, compared to these are this small atomic clock 120,000 times more exactly.)

application

atomic clocks serve for apart from accurate time measurement of expirations also to the exact Zeitbestimmung and coordination between different time systems and - scales. Soapproximately the coordinated world time from alignment of the internationally determined atomic time (TAI) with the astronomical time (UT1 ) ( UTC) results.

In Germany several atomic clocks are with the Federal Standards Laboratory (PTB) in Braunschweig in enterprise, under it also a cesium Fontäne in the rule enterprise. Over a long wave transmitterin Mainhausen Mainflingen with Frankfurt/Main all radio clocks receive, over the transmitter DCF77 their signal in Central Europe. The British counterpart to DCF77 is the transmitter MSF60. By means of Network Time Protocol (NTP) the Zeitimpulse of numerous atomic clocks are made available also in the Internet.

Onefurther atomic clock, however in form rubidium - atomic clock, serves the carrier frequency of the long wave broadcasting station there present in Donebach as oscillator for the production.

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