负折射率材料中二次谐波转换效率的理论分析

研究了二次谐波是负折射率而基频光是正折射率材料中，在考虑吸收系数、走离效应和相位失配的情况下，推导出平面波振幅缓变近似下，二次谐波的耦合波方程.根据该方程在基频光小信号近似下推导出二次谐波转换效率表达式.最后采用数值计算的方法分别研究了相位失配量Δk、走离角ρ和二次谐波的吸收系数α对转换效率的影响.结果表明，由于相位失配量的存在二次谐波的转换效率随负折射率材料长度的变化存在极大值，即负折射率材料长度存在最佳值，并且随着长度的增加，转换效率呈明显的周期性振荡并且极大关键词：负折射率材料二次谐波转换效率相位匹配

Theoretical analysis of second-harmonic conversion efficiency in negative-index materials

For negative-index materials(NIM) of second-harmonic wave(SHW) and positive-index materials of fundamental frequency wave(FFW)，the equations of the coupled wave was deduced，taking account of absorption coefficient，walk-off effect，phase mismatching capacity and the approximation of slow-varying amplitudes of the plane wave. On the basis of the equations，a formulation of SHW conversion efficiency was obtained in condition of small signal approximation for FFW. Through numerical simulation, the effects of phase mismatching capacity，walk-off angle and absorption coefficient of SHW on the conversion efficiency of SHW were scrutinized respectively. The maximum conversion efficiency of SHW was realized via increasing the length of NIM，that is，there exists an optimum length of NIM; however, the conversion efficiency of SHW shows an evidencet periodic evolution and the maximum conversion efficiency always diminishes. The conversion efficiency decreases with the increases of the phase mismatching capacity and the absorption coefficient. The influence of walk-off effect is not evident so that it may be neglected with respect to the conversion efficiency of SHW. This study provides a basis for investigating nonlinear theory of negative-index materials.