双波泵浦非对称量子阱的光学整流效应

Nonlinear Optical Rectification of Asymmetric Quantum Well Based on Dual Pump

为了实现基于光整流方式的室温下宽调谐高效率太赫兹源,设计了一种适于双波长CO2激光器共振子带跃迁泵浦的双阱嵌套形非对称量子阱结构,结构组分为Al0.5Ga0.5As/Ga As/Al0.2Ga0.8As,采用密度矩阵及迭代方法计算了其二阶非线性光整流系数χo(2)表达式,在导带为抛物线形和非抛物线形两种条件下对χo(2)进行对比研究。计算结果表明,其偶极跃迁矩阵元随量子阱总阱宽的增大而逐渐减小。当固定量子阱总阱宽及其中一束泵浦光波长不变时,χo(2)随着另一束泵浦光波长的增加,呈现出先增大后减小的变化趋势。当深阱为7 nm、总阱宽为23 nm、两束泵浦光相等为10.64μm时,χo(2)达到最大值5.925×10-6m/V;随着总阱宽的增大,χo(2)曲线呈现"红移"现象,其原因为量子限制效应导致了不同阱宽条件下的量子阱能级值差不同,从而造成满足泵浦光光子能量与能级差共振条件的变化。导带为抛物线形和非抛物线形两种条件下的χo(2)的最大值对应泵浦光波长基本相同,χo(2)数值上的差异主要由跃迁矩阵元的不同导致。

Based on excitation from a dual-wavelength CO2 laser, the optical rectification （OR） in a multiple asymmetric quantum well （AQW） was theoretically investigated by using the compact den- sity matrix approach and the iterative method. The numerical results for the typical Al0.5 Ga0.5 As/ GaAs/Al0.2Ga0.8As material show that the dipole matrix element decreases with the increasing well width of the AQW. Moreover, the optical rectification coefficient depends sensitively on two pump light wavelengths and well width of the AQW. The physical origin of this shift in optical rectification curve is the quantum confinement effect in the AQW system which causes the separation of energy levels and the changes in resonant condition. For an AQW of 7 nm deep well-width and 23 nm shallow well-width, the maximum of optical rectification coefficient for the AQW is 5. 925 × 10-6 m/V when the two pump wavelengths are all 10.64 μm. The characteristics of optical rectification are al- so analyzed on parabolic and non-parabolic energy-band conditions in detail.