Modulating nonlinear optical responses in 3R-MoS$_2$ Fabry-P\'erot microcavities

TL;DR

This paper develops a comprehensive framework to understand and control nonlinear optical responses in 3R-MoS₂ Fabry-Pérot microcavities, highlighting the interplay of material absorption and cavity effects.

Contribution

It introduces a self-consistent model that decouples geometric and material influences on harmonic generation in 3R-MoS₂, guiding the design of advanced van der Waals photonic devices.

Findings

Nonlinear emission is governed by a balance between material absorption and Fabry-Pérot effects.

Weak absorption allows complex modulation of nonlinear spectra by FP effects at multiple frequencies.

Strong absorption dampens FP effects at harmonic frequencies, limiting nonlinear response.

Abstract

Rhombohedrally stacked transition metal dichalcogenides such as 3R-MoS$_2$ offer an exceptional platform for nonlinear optics, naturally forming Fabry-P\'erot (FP) microcavities due to their giant dielectric contrast with the surrounding media. However, rigorously tracking the evolution of multiple harmonic fields within these unpatterned monolithic crystals remains a fundamental challenge. Here, we establish a self-consistent framework, spanning from linear broadband reflectance to second- and third-harmonic generation (SHG and THG), to systematically decode these nonlinear behaviors. Moving beyond conventional models, we demonstrate that the nonlinear emission is dictated by a delicate interplay among the intrinsic material absorption, the FP effects at the fundamental frequency, as well as those at the harmonic frequencies. When harmonic photons lie below the bandgap, weak absorption allows the nonlinear spectra to exhibit a complex modulation driven by the synergistic contribution of FP effects from both fundamental and harmonic waves. In stark contrast, severe intrinsic absorption of higher-energy photons heavily damps the FP effects of the harmonic fields, reducing the nonlinear response to an absorption-limited regime modulated almost exclusively by the FP effects at the fundamental frequency. By successfully decoupling these geometric and material contributions across different harmonic orders, our findings provide a precise design paradigm for engineering next-generation van der Waals photonic architectures.