The Study On Quantum Interference And Optical Emission In Atomic, Molecular And Ionic Multi-level Systems

The research for quantum interference in atoms, molecules and ions is an interesting topic in the field of laser physics and quantum optics. Many novel physical phenomena such as coherent population trapping, lasing without inversion, electromagnetically induced transparency as well as spontaneous emission cancellation and enhancement based on quantum interference have been discovered. Besides the important academic values, the research for quantum interference in multi-level systems has also promising applications.In the thesis, we theoretically investigate some influential factors for the quantum interference. We study the Doppler broadened effect on the continuous inversionless gain. The calculated results show that the generation of inversionless gain in Doppler-broadened media for a probe field wavelength in much excess of coupling field wavelength is possible, although the coupling field Rabi frequency is significantly less than the Doppler width. We also put forward a new influential factor for the quantum interference -FWM (four-wave mixing) field for the first time, and analyze the effect of four-wave mixing field on the electromagnetically induced transparency. It is found that the FWM field can cause the asymmetry of electromagnetically induce transparency profile. In addition, the effect of different propagating orientations of probe field on the electromagnetically induced transparency is also discussed.In the molecular multi-level system with the perturbed superposition levels, we discuss the electromagnetically induced transparency, spontaneous emission enhancement, double dark resonance and double electromagnetically induced transparency by using the density matrix equation under Weisskopf-Winger approximation and dressed-state density matrix equation. We analyze the influences of the perturbed energy-level space and superposion, laser power and intermediate level offset on quantum interference. Experimentally, in the sodium dimmer rhomb-type four-level system with a pair of perturbed levels, the interferenceenhancement of two-photon absorption caused by coherent superposition of the perturbed levels is experimentally observed. The calculating results agree with the experimental results.We also experimentally observed the effect of sodium atom-molecular collisions and sodium atom-atom collisions on the line-shape and intensity of fluorescence spectra. In addition, the optically pumped infrared stimulated emission and energy transfer up-conversion process are observed in Pr3+: Y2SiO5, and with the threshold energy, temperature dependence and divergence angle for the stimulated radiation are measured.