Deng Jian-Liao

Gain and Absorption of a Probe Light in an Open Tripod Atomic System

We theoretically investigate an open four-level atomic system interacting with control, probe and microwave fields. When there is no repumping light and a microwave field is applied, the probe light can be absorbed or amplified, which has different features than those of a system whose populations are pumped into only one ground state. In this system the microwave field and the population distributions of the ground states can be used as switches to control the propagation of the probe light.

Frequency-Shift of a Frequency Stabilized Laser Based on Zeeman Effect

We introduce a new method of frequency-shifting for a diode laser in laser cooling experiments, the method is based on the Zeeman effect of 87Rb atoms. The laser frequency is stabilized by absorption spectrum line of atoms in magnetic field. We show that a magnetic field can be added up to 10-2T. The corresponding frequency shift is 102MHz and the response time is about 1 ms. The large range of the frequency shift is sufficient for laser-cooling experiments.

Pulsed optically pumped rubidium clock with ultrahigh resonance contrast

In this paper, we report a dispersive detection technique with ultrahigh resonance contrast based on magneto-optical effect. To demonstrate specifically the advantages of the dispersive detection, we applied it in the pulsed optically pumped (POP) clock to obtain the clock signal. The contrast of Ramsey central fringe versus the parameters of pumping light, detection light and microwave power are studied experimentally. An ultrahigh resonance contrast greater than 90% is obtained. The frequency stability of POP clock in terms of Allan deviation for dispersive detection is improved by an order of magnitude over the absorptive detection under equivalent condition. We also present the preliminary experimental result in case of off resonance detection where a laser with large frequency detuning is used as detection light. The signal intensity detected by off resonance light is improved about 70% than the resonant light.

Temperature Dependence of Dark Lines in Coherent Population Trapping

We measure the signal amplitude and linewidth of a dark line in coherent population trapping in the Rb vapour cell filled with mixed buffer gas N-2 and Ar as a function of cell temperature. We find that the dark line signal amplitude increases with temperature up to a maximum at 49 degrees C and then drops at higher temperatures due to quenching effects of N-2. The linewidth of the dark line remains basically constant, at 1080 Hz. We also measure the linewidth of the dark line as a function of laser intensity. The linewidth increases linearly with laser intensity. An intrinsic linewidth (FWHM=896 Hz at 3.4 GHz) of the Rb cell is obtained.

Transient responses of transparency in a far-off resonant atomic system

Transient coherent oscillations in a closed Λ system under far-off resonant Raman fields were investigated theoretically. It has been found that the coherent superposition of the ground states can be formed due to the absorption even for initial maximal mixed ground states. The absorption oscillates with a period depending on the two-photon detuning when the system is initially in a transparent state and the two-photon Raman detuning is suddenly changed. The amplitude of the absorption decays with the decay rate of the ground states, which is different from the case when the lasers are applied resonantly. These transient coherent oscillations can be used to measure the relaxation rate of the ground states.

Enhanced Kerr Nonlinearities Caused by Cross Talk Between Optical and Microwave Transitions

We investigate the enhanced Kerr nonlinearities in four-level atomic vapors driven by a coupling, probe and microwave fields. Under the optical one-photon and two-photon resonant conditions. the linear and nonlinear responses of the weak probe field call be modified by the cross talk among optical and microwave transitions. The enhanced Kerr nonlinearity can Form bright optical solitons of the probe field.

The dispersive properties of an excited-doublet four-level atomic system

We have investigated the dispersive properties of excited-doublet four-level atoms interacting with a weak probe field and an intense coupling laser field. We have derived an analytical expression of the dispersion relation for a general excited-doublet four-level atomic system subject to a one-photon detuning. The numerical results demonstrate that for a typical rubidium Dl line configuration, due to the unequal dipole moments for the transitions of each ground state to double excited states, generally there exists no exact dark state in the system. Close to the two-photon resonance, the probe light can be absorbed or gained and propagate in the so-called superluminal form. This system may be used as an optical switch.

Measuring Transmittance in Rubidium Vapour Cells Using an Extremely Weak Coherent Field of Light

The absorptive properties of the atomic transition in the Rb85 D2 (A) line (5S1/2-5P3/2) at 780.0 nm are measured by using a continuous tunable diode laser and a CCD detector in Rb vapour cell under the condition of extremely weak incident intensity. When the intensity of incident light decreases from 420 pW/cm2 to 0.03 pW/cm2, the transmittance is found to be independent of the incident intensity within our experimental accuracy.