Four-level System Of Cold Atoms, Four-wave Mixing Based On Atomic Coherence

In this thesis, we mainly investigate the nonline frequency inversion by quantum interference in a four ladder atomic system. My thesis is consisted of two parts:1. Frequency conversion on the transient process based on atomic coherence in a four-level ladder atomic systemIn this section, a four-level ladder atomic system, driven by two continued fields, is considered. We show that higher coherence and population transfer can be created between the ground state and the middle excited state. The short wavelength signal can be obtained by stimulated Raman when the probe pulse is input on the high excited state under transient condition. We show the condition for maximum frequency conversion efficiency by numerical simulation and theoretical analysis, and investigate the influences of the intensity of the two coherent fields,the pulsewidth, the detuning and the various parameters of the atoms on the frequency conversion efficiency.2. The contrast of the frequency conversion between on the transient process and on the steady process in a four-level ladder atomic systemIn this section, the result of the frequency conversion between on the transient process and on the steady process by numerical simulations are discussed, and the optimal idea for obtaining short wavelenth laser are shown by comparing and analyzing both of the two precess.