Investigation On The Coherent Reflection Of Optical Field Based On Atomic Coherence Effects

The interaction of the light with atoms, as a very important research content of the quantum optics, has thriving development in recent decades. Based on the generation of the interaction of coherent light with atomic medium, atomic coherence effects have received increasing attention. Atomic coherent is always accompanied by quantum interference, which caused many novel and interesting quantum phenomena.This dissertation reviews the traditional electromagnetic induction transparency (EIT) effect, introduces the present research situation and development direction of four-wave mixing which induced by the atomic coherence effects. More importantly, we focus on our research work in experiment and theory, which including the theoretical calculation of the dynamical process about bichromatic fields coupled EIT atomic system, experimental research and theoretical analysis of the coherent reflection induce by the standing-wave fields coupled different atomic level. Based on the atomic gas system, we first supply the theory that on the condition of phase mismatching in the process of four-wave mixing, anomalous dispersion compensates the phase mismatching, and furthermore, the interaction of four photons is analyzed in detail. We also demonstrate the necessary condition of realization on coherent reflection in different degenerate two-level systems (Fg>Fe, Fg=Fe and Fg<Fe). The main works are as following:1) The dynamical process about bichromatic fields coupled A-type EIT system has investigated theoretically, and the general form of density operator for the interaction of atoms with probe light is presented. Based on this, the property of absorption and dispersion of atoms to the probe light has investigated on the condition of standing-wave coupling fields. We find that when only the co-propagating coupling field is used, the absorption of atoms to the probe is very weak, and the dispersion is normal dispersion, that is classical EIT effect; however, when the travelling-wave coupling light is replaced by the standing-wave, the absorption of the probe is enhanced, and normal dispersion is changed to anomalous dispersion, EIT changes to electromagnetically induced absorption (EIA). So we deduce the higher order nonlinear coherent process (multi-wave mixing) may be generated in this system due to the standing-wave coupled.2) On the basics of theoretical analysis, at first, we observed experimentally the fact that the probe light through the atoms is changed from transparency to be vanished when increasing the power of counter-propagating via R from0to1. We also demonstrate that in the three-level Cs atomic system, the high efficiency coherent reflection signal is rather generated experimentally even when the frequency of fields are not satisfied with the condition of phase matching (or Bragg reflection), that is ωe>ωp. Comparing with the results of experiment, we supply the theory that the dispersion compensation, that is the phase mismatching is compensated for by anomalous dispersion due to the strong absorption of the probe.3) For further verify the universality of the theory on the dispersion compensation, we do research in experiment in the case that changing the energy levels acted by the coupling and probe lights, in which the frequencies of all fields should be satisfied with the condition of phase matching (for Cs atom Di line, the phase matching angle is θ=0.42°), and the generation of coherent reflection is demonstrated experimentally. Furthermore, we also measure the relation of coherent reflection with the probe's frequency detuning. We also theoretically elaborate the four-wave mixing process on the condition of phase matching and phase mismatching, respectively, and the theory of dispersion compensation interpret the experimental results well. The high reflection efficiency of signal are also generated in wide range of detuning of the coupling fields and the results have many potential applications in quantum optics and quantum information, such as the multi-channel information processing, tunable optical switching.4) The coherent reflection is also investigated experimentally in the case of degenerate two level systems (where the frequencies of coupling and probe light are equal), which includes three sorts:Fg>Fe, Fg=Fe and Fg<Fe, where Fg and Fe represent the angular momentum of ground state excited state, respectively. Furthermore, the reflection spectra with an asymmetric profile as the function of one-and two-photon detunings are obtained, which is theoretically explained by the phase mismatch compensation during the process of four-wave mixing in an atomic system. This shows that under the condition of coherent population trapping the nonlinear reflection can be improved with one-and two-photon detunings in a degenerate two-level system. And these results expand the application of coherent reflection due to the atomic nonlinear effects.The characterized works among the above are as follows:Ⅰ. In a hot atom system, the coherent reflection signal with high efficiency is obtained at the case that the frequencies of interacting fields are not satisfied with the condition of phase matching (or Bragg reflection), and the relation of coherent reflection with probe detuning is also investigated in different condition of standing-wave. In theory, based on four-wave mixing process, we supply the theory of anomalous dispersion compensate the phase mismatching.Ⅱ. Based on the dispersion compensation, we compare the relation of coherent reflection at the case that the frequencies of coupling and probe lights are and are not satisfied with the condition of phase matching. We also investigate the change of intensity of co-and counter-propagating fields after interacting with atoms, and the experimental results supply the physical mechanism of four-photon interaction. The atoms absorb the probe and the counter-propagating coupling field, and meanwhile emit the co-propagating coupling field and the reflected field. The probe and the co-propagating coupling field form a Doppler-free pair, and the reflected and the counter-propagating coupling fields form another Doppler-free pair, so that we have Doppler-free reflection, because both pairs are at two-photon resonance. In fitting the theory to the experiment, we put forward to the concept of effective length, and find that it play the key action in the case of phase mismatching.Ⅲ. The coherent reflection is also investigated experimentally in the degenerate two level systems. We find that in the same experimental parameters, different level structures cause different results:when Fg>Fe, the reflection efficiency is highest; and when Fg=Fe, the reflection intensity is much smaller than that in the case of Fg>Fe, but the line-width of signal is narrower than that above. However, when Fg<Fe, no reflected signal is generated. Based on the results above, we deduce the necessary condition of generating coherent reflection in the degenerate two level systems. In the degenerate two-level systems, only the Zeeman sublevels include stable A-links, that is the population are trapped in the ground states, can exhibit steep absorption and reflection of the probe light with a standing-wave coupling.