张彦鹏，学者凯发k8国际首页主页-凯发网

we report detailed experimental studies of enhanced fluorescence intermittency in mn-doped single znse quantum dots. a the measured intermittency statistics and its dependences on the excitation intensity and dot size indicate that the enhanced blinking might be due to the strong coupling between the multiple mn2 ions within a single nanocrystal. a the measured statistical results are compared with a diffusion-controlled electrontransfer model, which gives the diffusion rates for the "on" and "off" time distributions.

we theoretically investigate the dually dressed electromagnetically induced transparency, and the multidressed four-wave mixing (fwm) and six-wave mixing (swm) processes in an inverted-y-type atomic system with zeeman sublevels. a the results show that the zeeman degeneracy of the dark states can be lifted by the dressing field as its intensity is increased. amoreover, the derived analytical expressions indicate that one can, for example, selectively create secondary dark states on the multi-zeeman-sublevel dark states (by tuning the coupling field0, distinguish two different types of dark states generated in two fwm processes (by properly controlling the coupling field intensity), and selectively enhance multi-fwm signals coming from various paths consisting of split zeeman sublevels (by tuning the dressing field). a the swm signals can be either enhanced or suppressed by controlling the dressing field.

using phase control between four-wave mixing (fwm) and six-wave mixing (swm) channels in a four-level atomic system, we demonstrate temporal and spatial interferences between these two nonlinear optical processes. a efficient and coexisting fwm and swm signals are produced in the same electromagnetically induced transparency window via atomic coherence. a the temporal interference has a femtosecond time scale corresponding to the optical transition frequency. asuch studies of intermixing between different order nonlinear optical processes with a controllable phase delay can have important applications in high-precision measurements, coherence quantum control, and quantum information processing.

we present a fully time dependent, adiabatic solution, and steady-state analysis for the ultraslow propagation of the nondegenerate four-wave mixing _ndfwm_ signal and the weak probe beam in a closely-cycled double-ladder system. a under appropriate _especially power balance_ conditions, the two-mode probe and phase-matched ndfwm pulses, after a characteristic propagation length, evolve into a pair of amplitude and group velocity matched pulses. a double transparency for the probe and ndfwm beams can be achieved owing to an efficient one- and three-photon destructive interference involving the ndfwm beam and its back reaction to the probe beam. a the forward and backward configurations are investigated in this double-ladder system, and their efficiencies are calculated and compared.

we demonstrate efficient energy exchange during propagation between four-wave-mixing (fwm) and sixwave- mixing (swm) signals generated in a four-level inverted-y atomic system, which fall in the electromagnetically induced transparency window. aafter an initial growth distance for both fwm and swm fields in the atomic medium, these two nonlinear optical processes compete and exchange energy between them, and eventually reach their respective steady-state values at long interaction distance. a this energy exchange phenomenon can be explained by considering established atomic coherences among various atomic states and quantum interferences between three-photon and five-photon excitation pathways. a understanding these highorder nonlinear optical processes and interplays between them can be very important for correlated fwm (or swm) photon-pair generations and quantum information processing.

we report our observations of enhancement and suppression between two competing four-wave mixing _fwm_ processes. a the results show the evolution of the dressed effects _from pure enhancement into pure suppression_ in the degenerate fwm processes. amoreover, due to induced atomic coherence in the system, there exist different interplays between these two fwm processes via different detuning parameters. ain addition, the power dependences of enhancement and suppression are studied. atheoretical calculations are carried out, which are in good agreement with the experimental observations.

we investigated the influence of self-diffraction effect on femtosecond cross pump-probe optical kerr shutter (oks) measurements for fast response and slow response materials, respectively. ain the slow response material of cs2, a fast response resulted from self-diffraction effect was observed in the time-resolved oks signals, and the signal intensity showed different pump power dependences at different delay time. afor the fast response material of bismuth oxide (bi) glass, the pump power dependence of oks signals varied when the polarization angle was varied. a the pump power dependences of oks signals for the both materials showed that, the oks signals resulted mainly from laser induced birefringence effect at low pump powers, and the contribution of self-diffraction effect to oks signals was enhanced with increasing the pump power.

four-level polarization beats (flpbs) with broadband noisy light are investigated by use of chaotic field, phase-diffusion, and gaussian-amplitude models. a the polarization beat signal is shown to be particularly sensitive to the statistical properties of the markovian stochastic light fields with arbitrary bandwidth. adifferent stochastic models of the laser field affect only the fourth-order coherence functions. a the constant background of the beat signal originates from the amplitude fluctuation of the markovian stochastic fields. a the gaussian-amplitude field shows fluctuations larger than the chaotic field, which in turn exhibits fluctuations much larger than for the phase-diffusion field with pure phase fluctuations caused by spontaneous emission. ait is also found that the asymmetric behaviors of the polarization beat signals due to the unbalanced dispersion effects between the two arms of an interferometer and to the doppler width do not affect the overall accuracy when flpbs are used to measure the energy-level difference between two states that are dipolar forbidden from the ground state.

based on the phase-conjugate polarization interference between two-pathway excitations, we obtained an analytic closed form for the second-order or fourth-order markovian stochastic correlation of the v three-level sum-frequency polarization beat ssfpbd in attosecond scale. anovel interferometric oscillatory behavior is exposed in terms of radiation-radiation, radiation-matter, and matter-matter polarization beats. a the phasecoherent control of the light beams in the sfpb is subtle. awhen the laser has broadband linewidth, the homodyne detected sfpb signal shows resonant-nonresonant cross correlation, a drastic difference for three markovian stochastic fields, and the autocorrelation of the sfpb exhibits hybrid radiation-matter detuning terahertz damping oscillation. aas an attosecond ultrafast modulation process, it can be extended intrinsically to any sum frequency of energy levels. ait has been also found that the asymmetric behaviors of the polarization beat signals due to the unbalanced controllable dispersion effects between the two arms of interferometer do not affect the overall accuracy in case using the sfpb to measure the doppler-free energy-level sum of two excited states.

based on three stochastic models, the subtle, markovian field-correlation effects have been investigated in homodyne-detected attosecond sum-frequency raman-enhanced polarization beating (repb) and heterodynedetected femtosecond difference-frequency repb. a the different roles of the amplitude fluctuations and the phase fluctuations have been pointed out in both time and frequency domains. aanalytic closed forms of the sixth-order and fourth-order markovian stochastic correlations are characterized for homodyne (quadratic) and heterodyne (linear) detection, respectively. a the attosecond sum-frequency repb signal shows resonant- nonresonant cross correlation, asymmetric temporal behavior, and drastic difference for three markovian stochastic fields, and the autocorrelation of repb exhibits hybrid-radiation-matter-detuning-terahertz damping oscillation. a the phase-diffusion model predicts a damping oscillation of the signal around a constant value in the narrowband case. a the heterodyne-detected signal of repb potentially offers rich dynamic information about the homogeneous, broadening, material phase of the third-order nonlinear susceptibility.