针对拉曼驱动场下的四能级理论模型，讨论了实现无吸收、高折射率的条件，并分析了探测场及相干激发场的线宽对介质的折射率及增益的影响。计算结果表明，改变相干激发场的场强，或改变相干场的频率与原子能级间的失谐均可获得介质的无吸收、高折射率。激发场线宽破坏了原子的相干性，使介质的增益下降并改变了折射率的大小，探测场的线宽使介质的探测增益谱及折射率谱的分辨率下降。 According to the four-level theoretical model of Raman driving field, the condition of non-absorption and high refractive index is discussed. The influence of the linewidth of the detection field and coherent excitation field on the refractive index and gain of the medium is analyzed. The calculated results show that the non-absorption and high refractive index of the medium can be obtained by changing the field strength of the coherent excitation field or by changing the detuning between the frequency of the coherent field and the atomic level. Excitation field line width destroys the coherence of the atoms, reducing the gain of the medium and changing the size of the refractive index. The linewidth of the detection field decreases the resolution of the detection gain spectrum and the refractive index spectrum of the medium.