Subwavelength Coherent Scaling of High-Order Nonlinear Light Generation in Bulk Monolayer MoS2 Thin Films

TL;DR

This paper demonstrates that bulk monolayer MoS2 thin films significantly enhance high-order nonlinear light generation through layered superstructures, enabling scalable, efficient, and tunable nonlinear optical processes in a sub-wavelength regime.

Contribution

The study introduces a solution-processed layered MoS2 architecture that preserves nonlinear susceptibility while enabling scalable interaction length for enhanced nonlinear light generation.

Findings

NLG scales nearly quadratically with layer number (N^1.8) in sub-wavelength regime.

A 100-nm BM-MoS2 film exhibits nonlinear signals nearly 100 times stronger than a 3-mm ZnSe crystal.

Broad spectral tunability over 1000 nm in the mid-IR range achieved.

Abstract

Monolayer transition metal dichalcogenides (e.g., MoS2) exhibit exceptionally large optical nonlinearities for high-order nonlinear light generation (NLG), yet their inherent atomic thickness fundamentally limits light-matter interactions and thus conversion efficiency. Here, we overcome this intrinsic trade-off using a solution-processed bulk monolayer MoS2 (BM-MoS2) architecture composed of electronically decoupled MoS2 monolayers separated by organic interlayers. This layered superstructure preserves the exceptional intrinsic nonlinear susceptibility of monolayer MoS2 while enabling scalable interaction length. In the sub-wavelength regime, the NLG scales nearly quadratically with layer number (N^1.8), confirming the constructive buildup of nonlinear fields across stacked monolayers. As a result, a 100-nm-thick BM-MoS2 thin film exhibits colossal high-order NLG, including four-wave mixing and high harmonic generation nearly two orders of magnitude stronger than those from a 3-mm-thick ZnSe crystal. The generated nonlinear beam is directly visible to the naked eye and exhibits broad spectral tunability spanning more than 1000 nm in the mid-IR, enabling mid-IR-to-visible upconversion spectroscopy for resolving molecular vibrational fingerprints. By uniting monolayer-scale nonlinear susceptibility with bulk interaction length and coherent field buildup, BM-MoS2 establishes a thin-film platform for ultra-compact and substrate-agnostic nonlinear photonic systems beyond the constraints of conventional single crystals.