Du Chun-Guang

Transparency and Strong Gain Without Population Inversion in Photonic Bandgap Crystals

Without using the weak-field approximation, we investigate the transient properties of a Λ-type atom with one transition near resonant with a photonic bandgap edge. Whatever the initial state of the atom is, the atom can become transparent to a probe field, and strong gain without population inversion is also possible if the atom has been pre-excited. The defect mode formed by atomic doping can have a strong effect on the absorption properties of the atom.

Incoherently Coupled Bright-Dark Soliton Pairs in Biased Centrosymmetric Photorefractive Media

It is shown theoretically that incoherently coupled bright-dark soliton pairs can exist in biased centrosymmetric photorefractive media under steady-state conditions. These soliton pairs can be established provided that the two optical beams have the same polarization, wavelength, and are mutually incoherent.

Manakov Soliton Pairs in Biased Photovoltaic Photorefractive Crystals

We study, theoretically, incoherently coupled screening-photovoltaic soliton pairs in biased photovoltaic photorefractive crystals. It is shown that when the total intensity of two coupled solitons is much lower than the effective dark irradiance, the coupled soliton equations reduce to the Manakov equations. The dark-dark, bright-bright and dark-bright soliton pair solutions of these Manakov equations are obtained under an appropriate external bias field and a photovoltaic field, and the characteristics of these Manakov soliton pairs are also discussed in detail.

Light-induced nonlinear effects on dispersion relation of ultracold Bose gas

We have investigated the optical properties of Λ-configuration ultracold dense Bose gas interacting with two laser pulses, which usually result in electromagnetically induced transparency. With the nonrelativistic quantum electrodynamics and taking into account the atomic dipole-dipole interaction and local field effect, we have derived the Maxwell-Bloch equations of the system. The dispersion relation of an ultracold Bose gas has been obtained and the light-induced nonlinear effects have been analysed. The light-induced nonlinear effects are different from the effects induced by two-body collision of Bose-Einstein condensation atoms which have a frequency shift of transparent window.

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.

Slow Light by Modified Reservoir Induced Transparency with a Non-Singular Density of Modes

We investigate the dispersive property of a ?-type atomic system embedded in photonic band gap structures. The atomic coherence is established by the structured reservoir which consists of a double-band photonic band gap (PBG) and defect modes. With an atomic density of 7?1015?atoms/cm3, the group velocity of a probe laser being detuned far away from the gap is shown to be reduced to 3?102?m/s near the transparency window associated with the PBG edges and 6?103?m/s at the transparency window associated with the defect modes, without using any deriving field. The influence of the smoothness of the density of modes and the decay rate of the second ground state of atoms are analysed.

Nonadiabatic effects on population transfer of two Bose-Einstein condensates induced by atomic interaction

We investigate the stimulated Raman adiabatic passage for Bose-Einstein condensate (BEC) states which are trapped in different potential wells or two ground states of BEC in the same trap. We consider that lasers are nearly resonant with the atomic transitions. The difference of population transfer processes between BEC atoms and usual atoms is that the atomic interaction of the BEC atoms can cause some nonadiabatic effects, which may degrade the process. But with suitable detunings of laser pulses, the effects can be remedied to some extent according to different atomic interactions.

Atomic Interaction Effects on Electromagnetically Induced Transparency and Slow Light in Ultracold Bose Gas

We investigate electromagnetically induced transparency and slow group velocity of light in ultracold Bose gas with a two-photon Raman process. The properties of electromagnetically induced transparency and light speed can be changed by controlling the atomic interaction. Atomic interaction can be used as a knob to control the optical properties of atomic media. This can be realized in experiment by using the Feshbach resonance technique.

Stimulated Raman Adiabatic Population Transfer of Two Bose-Einstein Condensates

Considering all the ground-state atom interactions, we investigate the population transfer of two Bose-Einstein condensate (BEC) states, which are trapped in different potential wells, or two ground states of the BEC in the same trap using the stimulated Raman adiabatic process. With a proper choice of pulsed geometric parameters, the dark state exists. By simply choosing ground-state detunings, the effects of the interatomic interaction can be suppressed and a high population transfer rate can be obtained.