Yang Dong-Hai

Alternating Current Zeeman and Stark Interference Effect in Ramsey Separated Oscillating Fields

Analytic expressions have been derived of the alternating current (ac) Zeeman and ac Stark effect in an atomic beam magnetic resonance method using Ramsey separated oscillating fields. An interesting feature which will affect the normal Ramsey pattern is that an interference fringe is superimposed on the dispersion lineshapes of the normal ac Zeeman or ac Stark effect. We point out that this new character of ac Zeeman (ac Stark) effect generally exists in all kinds of Ramsey method, for example, in the optical Ramsey atomic interferometer and atomic beam frequency standard. An important implication is that, particularly in an atomic beam frequency standard using Ramsey method, this effect has an influence on the evaluation of the second-order Doppler frequency shift.

A Scheme for Realizing the Continuous Wave Atom Laser

We propose a scheme for realizing the long-term continuous output of an atom laser. In this scheme the cold atoms in several subsidiary Bose-Einstein condensates (BEC) will be coupled one by one in turn into one main BEC which serves for the continuous output of a coherent atomic beam. We discuss the process of the phase unification of the newly entered BEC atoms with the remaining atoms in the main BEC trap. An ideal dynamical equilibrium can be established when the transition rate of the uncondensed atoms transforming into the condensate and the decay rate of coupling output satisfy some conditions. The coupling method from the subsidiary BEC to the main BEC and the time rates of all different processes are considered.

Experimental Test of Alternating-Current Zeeman Interference Effect in Ramsey Separated Oscillating Fields

An experimental test of ac Zeeman effect in an optically pumped caesium beam frequency standard is reported and analysed. An interference pattern of the atomic energy level shift as a function of the applied microwave field near the atomic transition frequency was observed. It was superimposed on the dispersion lineshape of a normal ac Zeeman effect. This effect was analysed with the atomic wavefunction phase analysing method.

Dependence of electromagnetically induced transparency on temperature

We performed an experimental study on the dependence of the linewidth of electromagetically induced transparency (EIT) on the temperature of medium in a Λ-type configuration using caesium vapour. We found that the transparent window is narrowed in the EIT whose two ground levels are composed of two hyperfine levels and broadened in the case when the two ground levels are degenerated Zeeman sublevels, as the temperature of vapour cell is increased. The explanation for the phenomena is given qualitatively.

A New Pumping-Probing Scheme for the Optically Pumped Cesium Beam Frequency Standard

A new pumping-probing scheme for the optically pumped cesium beam frequency standard has been experimentally tested in our laboratory. The stability of the optically pumped cesium beam frequency standard was measured by comparing its 10 MHz output with an HP5071A commercial cesium atomic clock. The result shows that the frequency stability for the 1 s and 30000 s sample times are 1.2×10-11 and 3.7×10-13, respectively. It was proved that the new pumping scheme works well. PACS: 06. 20. Fn, 42. 62. Eh

High Performance Small Optically Pumped Caesium Beam Frequency Standard

An experiment of a high performance small optically pumped caesium (Cs) beam frequency standard is reported. An extended cavity diode laser works as the probing laser, of which the frequency is stabilized by the Zeeman modulation method. The running parameters of the frequency standard are dynamically optimized via digital servo electronics. The experimental setup improves the frequency stability up to 1.8×10−12 at τ = 1 s and about 1.0×10−13 at τ = 105 s (Allan deviation).

Evaluation of Light Frequency Shift in a Caesium Beam Frequency Standard with Sharp Angle Incident Detecting Laser

Light frequency shift measured in a small optically pumped caesium beam frequency standard is reported and analysed. Two light sources, the diffused laser light scattered from the caesium beam tube parts and the fluorescence light from the beam atoms excited by the laser light, for the light frequency shift are discussed.

Magneto-Optical Trap for Cesium Atoms Without a Separate Repumping Laser

A magneto-optical trap (MOT) for cesium atoms that operates without a separate repumping laser is reported. The differences between a normal MOT and this kind of MOT have been experimentally studied. The influences of a repumping laser on cooling and trapping cesium atoms in the MOT have been carefully investigated. The results reveal that it is the critical injection-locked state of the diode laser that makes magneto-optical trapping of cesium atoms possible without a separate repumping laser.

An Improved Magneto-Optical Trap for Cesium Atom

Based on the realization of magneto-optical trap for cesium atom in China, great improvement is achieved on its performance. In the new experimental setup, a laser battery in stepwise injection-locking scheme is developed as laser source, which has more output power and better beam quality than the previous one. Under the optimum working condition, cesium atoms of more than 109 with the density of 1011 atoms/cm3 are trapped to form an atomic cloud with the diameter of 3 mm. Compared with previous results, both the number of trapped atoms and the density of atomic cloud are increased in two orders of magnitude.

Experimental study on laser cooling of cesium atoms by optical molasses

We have studied the relationship between the temperature of Cs cold atoms and the parameters of the cooling laser. The atoms are first cooled and captured by a magneto-optical trap and then further cooled by optical molasses. The temperature of atoms is measured by a time-of-flight method. For relatively large laser intensity and small detuning, the temperature depends linearly on the intensity-to-detuning ratio, and nonlinear relationship has also been found in other case.