Thickness-dependence of Linear and Nonlinear Optical Properties of Multilayer 3R-MoS2

TL;DR

This paper introduces a fast, non-destructive optical method for measuring the thickness of 3R-MoS2 flakes and investigates how their linear and nonlinear optical properties, including harmonic generation, depend on thickness, revealing maxima related to Fabry-Pérot effects.

Contribution

It presents a novel optical technique for precise, rapid thickness measurement of 3R-MoS2 and explores the thickness-dependent nonlinear optical responses, advancing photonic applications.

Findings

Reflectivity-based thickness measurement with <2 nm bias.

Identification of thickness-dependent maxima in SHG and THG.

Maxima linked to Fabry-Pérot phase matching conditions.

Abstract

3R-MoS2, a MoS2 polytype with broken inversion symmetry, enables unique light-matter interactions and is promising for linear and nonlinear integrated photonics beyond the monolayer limit. Yet, systematic studies of its thickness-dependent reflectivity and its impact on harmonic generation are still lacking. . Yet, systematic studies of its thickness-dependent reflectivity and its impact on harmonic generation are still lacking. Here, we introduce a non-destructive optical method to determine the thickness of 3r-MoS2 flakes from reflectivity measurements, offering AFM-like precision with a mean bias of less than 2 nm range, while being much faster and applicable to non-solid substrates such as PDMS, in the 3-200 nm range. Nonlinear characterization further reveals distinct thickness-dependent maxima in second- and third-harmonic generation (SHG/THG), with the first clear peak at ~200 nm. These maxima arise from Fabry-P\'erot-type phase matching conditions mediated by the film thickness and can further be shaped by absorption. This work thus provides both a practical thickness metrology and new insights for exploiting thickness-dependent 3R-MoS2 nonlinearities in scalable photonic technologies.