基于共振Raman增强的三阶非线性过程

Enhanced third-order nonlinear processes based on Raman resonance

本文实验上观察到在85Rb原子蒸气D1线系统中,基于Raman共振的四波混频得到显著地增强;并且通过模拟看到,随着耦合光功率的减小或多普勒展宽的增大,信号线宽呈现被压窄的趋势.我们利用宏观极化干涉理论对光谱线宽的特点进行了分析,并诠释了在多普勒增宽L-型能级系统中的四波混频与电磁感应透明均来源于受激Raman散射,区别在于探测方式和对象的不同.

We observe experimentally huge enhanced four-wave mixing based on Raman resonance in an 85 Rb atomic vapor system. With the decrease of coupling field power or the increase of experimental temperature, the signal tends to be narrowed down in linewidth, and be basically the same spectrum as the stimulated Raman spectroscopy. It is found that the macroscopic polarization interference effect plays a crucial role in determining the nonlinear spectra. Further more, in the Doppler-broadened L-type energy level system, there is a strong relationship among electromagnetically induced transparency, four-wave mixing and stimulated Raman spectroscopy. The sharp transparent window in electromagnetically induced transparency can be interpreted as the suppression of Raman gain on the linear absorption of the probe field. However, the four-wave mixing signal is a new field generated by the atomic vapor system, and it comes from the Raman gain which is affected and modified by the absorption and dispersion of the nonlinear optical medium. It shows that in a L-type Dopplerbroadened system, in essence, both the electromagnetically induced transparency and enhanced four-wave mixing stem from stimulated Raman scattering based on the third-order nonlinear processes, just the spectra of which are from different ways and objects of detection.