Giant optical nonlinearity cancellation in quantum wells

TL;DR

This paper demonstrates both theoretically and experimentally that giant cancellation effects in quantum wells can cause the second-order nonlinear susceptibility to vary dramatically, impacting optical nonlinearities and enabling sensitive bandstructure analysis.

Contribution

The study reveals how interference among quantum states causes large cancellations in nonlinear susceptibility, providing new insights and tools for quantum well optical property engineering.

Findings

Second-order nonlinear susceptibility varies by orders of magnitude due to cancellation effects.

Interference of light and heavy hole states causes giant nonlinear cancellations.

The work introduces a sensitive method for probing quantum well bandstructure.

Abstract

Second-order optical nonlinearities can be greatly enhanced by orders of magnitude in resonantly excited nanostructures, theoretically predicted and experimentally investigated in a variety of semiconductor systems. These resonant nonlinearities continually attract attention, particularly in newly discovered materials, but tend not to be as efficient as currently predicted. This limits their exploitation in frequency conversion. Here, we present a clear-cut theoretical and experimental demonstration that the second-order nonlinear susceptibility can vary by orders of magnitude as a result of giant cancellation effects in systems with many confined quantum states. Using terahertz quantum cascade lasers as a model source to investigate interband and intersubband resonant nonlinearities, we show that these giant cancellations are a result of interfering second-order nonlinear contributions of light and heavy hole states. As well as of importance to understand and engineer the resonant optical properties of materials, this work can be employed as a new, extremely sensitive tool to elucidate the bandstructure properties of complex quantum well systems.