For a space-borne hydrogen maser frequency standard, it is severely required to reduce the size and weight without degrading its excellent frequency stability. To meet these requirements, a small sized microwave cavity with high quality factor is necessary. In this paper, TE011 mode of a small sapphire loaded dielectric cavity for a space-borne hydrogen maser is analyzed and its design principle is discussed. The analysis shows that the frequency stability is optimized when the ratio of the outer diameter of the dielectric tube to the inner diameter of the cavity cylinder is about 0.5. The weight of the physics package is minimized when the diameter and the height of the cavity cylinder are equal to each other. The diameter or the volume of the cavity cylinder is determined by the frequency stability required in the application program.
Two field operable hydrogen masers were developed for the VLBI joint experiment conducted by the cooperation between RRL and NASA. They are now playing an important role as the time and frequency standard of the K-3 VLBI system, which has also been developed by RRL.
A cesium frequency standard based on the atomic fountain configuration has the potential of improving the accuracy of primary frequency standard. For the first step toward a realization of slow vertical atomic beam (that is an atomic fountain), we have succeeded to decelerate the horizontal cesium atomic beam by laser cooling with the Zeeman tuning method. Then those slowed atoms are confined with a magneto-optical trap by four laser beams in the tetrahedral configuration. By using these trapped atoms, one can launch them upward with the upstream laser pulses.< >
Frequency-stabilized and spectral-linewidth-narrowed laser diode systems are being developed for optical pumping of a cesium atomic clock. Frequency stabilization and reduction of spectral linewidth were carried out by utilizing optical feedback from a Fabry-Perot interferometer. Saturation absorption and fluorescence spectroscopy results are presented. It is shown that the long-term stability of optical locking is not sufficient for a practical atomic clock.< >
Microwave Rabi Resonances of Cs atom are observed by using optical pumping and optical detection with a laser diode. In case of Δ F=0, π porahzed pumping light, mF=0 atoms remain in the same magnetic sublevel. This result leads to the realization of pumping all Cs atoms into a mF=0 single magnetic sublevel by the, use of two lasers.
The Majorana effect on the hydrogen maser and the cesium (Cs) beam frequency standard is studied. In the hydrogen maser, the Majorana transition is used to the state selection successfully to eliminate the atoms in the [F = 1, mF = 1] state. As the result, a good performance of the hydrogen maser operation is obtained. In the Cs beam frequency standard, the remarkable phenomena due to this transition are described, such as the change of beam detection current, the change of the pattern in the low-frequency Zeeman transition, and the change of the velocity distributions.
Summary The results of the operation of the hydrogen maser with a ne'v. state selector are described. In the first part of this report, the measurenent results of the magnetic inhomogeneity shift of the maser frequency by the use of a new state selector are described. In the next part, the results of the long-term continuous operation of the masers by the automatic cavlty tuning method are described. Maser structure and Electronics 'The structure of the maser, H3 or H4, is shown in Fig.1. It is of the loboratory type. This apparatus consists of the two ion pumps, the atomic source system, the double focuslng state selector, the four-layer magnetic shields, the microwave cavity and the storage bulb. The shielding factor is about 15000. The loaded Q of the cavity is about 45000 and the cavity temperature 1s controlled within the limits of 10.01 C. the cavity autotuning electronics are shown in Fig.2. The system shown In the upper part of the figure is the phase-locking loop for controlling aMHz quartz crystal oscillator. The system shown in the lower part is the electronics for the automatic cavity tuning1. The beat priod of the two maser frequencies is measured to detect the cavity offset by varying the atomic flux between the two levels. The detected signal is used to correct the cavity frequency. The frequency stability of the free running maser is about 3 x at the averaging time of 500 seconds and that of the autotuned maser is about 1 x at the averaging time from 100 seconds to 1 day. The system of the maser electronics and that of
