Free electron nonlinearities in heavily doped semiconductors plasmonics

TL;DR

This paper explores nonlinear optical effects in heavily doped semiconductors, revealing significant third-harmonic generation and potential for advanced mid-infrared plasmonic devices.

Contribution

It introduces a hydrodynamic model for free electron nonlinearities, showing cascaded third-harmonic generation and enhanced nonlinearities in doped semiconductors.

Findings

Cascaded third-harmonic generation can rival direct third-harmonic signals.

Nonlinearities can be amplified by plasmonic enhancement, up to 100 times.

Potential for new mid-infrared nonlinear optical devices.

Abstract

Heavily doped semiconductors have emerged as tunable low-loss plasmonic materials at mid-infrared frequencies. In this article we investigate nonlinear optical phenomena associated with high concentration of free electrons. We use a hydrodynamic description to study free electron dynamics in heavily doped semiconductors up to third-order terms, which are usually negligible for noble metals. We find that cascaded third-harmonic generation due to second-harmonic signals can be as strong as direct third-harmonic generation contributions even when the second-harmonic generation efficiency is zero. Moreover, we show that when coupled with plasmonic enhancement free electron nonlinearities could be up to two orders of magnitude larger than conventional semiconductor nonlinearities. Our study might open a new route for nonlinear optical integrated devices at mid-infrared frequencies.