Takao Morikawa

The New Generation System of Japan Standard Time at NICT

NICT has completed a new generation system for the realization of Japan standard time. There are various renewals in this system. One of the big changes is the introduction of hydrogen masers as signal sources for UTC(NICT) instead of Cs atomic clocks. This greatly improves the short-term stability of UTC (NICT). Another big change is the introduction of a newly developed 24ch dual-mixer-time-difference system (DMTD) as the main tool for measurements. The reliability of the system is also improved by enhanced redundancy and monitoring systems. The new JST system is in regular operation since February 2006.

Accuracy evaluation of optically pumped primary frequency standard CRL-O1

In cooperation with the Time and Frequency Group of the National Institute of Standards and Technology, the Communications Research Laboratory has developed an optically pumped primary frequency standard (PFS) which is named CRL-O1. The accuracy of CRL-O1 has been evaluated and reports have been sent to the Bureau International des Poids et Mesures. The results of the evaluations have been published in Circular T. We estimate the biases of the frequency shifts and the so-called type A and type B uncertainties. The combination of type A and type B uncertainties is about 7 × 10−15. The evaluated frequency of CRL-O1 is in good agreement with that of other PFSs.

Atomic Collimation with a Single Laser Pulse

In this letter we describe a new method of reducing one or two components of atomic velocity using an optical dipole force. The optical dipole force produces a harmonic potential transverse to the Gaussian optical beam. If the initial atomic position is close to the center of the beam, the transverse velocity component becomes almost zero after a quarter period of harmonic oscillation. If the laser is switched off at this moment, a very small transverse velocity component can be obtained. The use of a far-detuned laser reduces the heating due to spontaneous scattering and enables us to obtain a sub-photon recoil velocity component.

Update of research activities on time and frequency at the National Institute of Information and Communications Technology (NICT)

The National Institute of Information and Communications Technology (NICT) in Japan have five time and frequency research and service groups. Those are, Atomic Frequency Standards Group, Time and Frequency Measurements Group, Japanese Standard Time Group, Quasi-Zenith Satellite System Group, and Time Applications Group. In this paper, we introduce the recent activities of these five groups.

Development of Cs atomic fountain frequency standard at CRL

Communications research laboratory (CRL) has been developing a Cesium atomic fountain primary frequency standard. Cs atoms are cooled to below 2 /spl mu/K by both magneto-optical trap (MOT) and polarization gradient cooling (PGC), and launched vertically by moving molasses method. The launched atoms pass through a microwave cavity twice, on the way upward and downward, and give rise to Ramsey resonance. We succeeded to observe narrower than 1Hz Ramsey signal, and tried to lock the microwave frequency to the atomic resonance. This report presents the current status of the development of CRL atomic fountain.

ANOMALOUS TIME-OF-FLIGHT SIGNALS FROM POLARIZATION-GRADIENT-COOLED ATOMS

The time-of-flight signal from polarization-gradient-cooled Cs atoms indicates that the cooling effect first decreases with increased detuning, but is restored as the detuning is increased beyond -170 MHz. It also indicates that this detuning also causes a shift in the signal peak. These penomena can be explained by taking into account the influence of the neighboring transition.