Optical nonlinearity due to intersubband transitions in semiconductor quantum wells

摘要

We have calculated the contribution of intersubband transitions to the thirdorder optical nonlinear susceptibility, $\chi^{(3)}(\omega,\omega,\omega)$ fornonresonant as well as resonant third harmonic generation and$\chi^{(3)}(\omega,-\omega,\omega)$ for nonlinear refraction and absorption. Asexamples, we consider InAs/AlSb and GaAs/GaAlAs quantum wells. The effects offinite barrier height, energy band nonparabolicity, and high carrierconcentrations are included. It is shown that quantum confinement, rather thanthe band nonparabolicity, is responsible for high values of nonresonant$\chi^{(3)}_{zzzz}$. Very high values of $\chi^{(3)}_{zzzz}$ are obtained forthird harmonic generation and two photon absorption for incident wavelengthnear 10.6 $\mu$m. Intensity dependence of refractive index and of absorptionco-efficient is also discussed for intensity well above the saturationintensity. Effective medium theory is used to incorporate the collectiveeffects.