Nonlinear Optical Properties of Two-Dimensional Transition Metal Dichalcogenides for Ultrafast Photonics

Abstract

The two-dimensional transition metal dichalcogenides (TMDCs) have emerged as promising materials for ultrafast photonic technologies due to their strong light-matter interactions, layer-dependent band gaps, and nonlinear optical responses. Nevertheless, their nonlinear behavior under ultrafast excitation remains poorly understood, posing a major challenge for practical integration. This paper examines the optical characteristics of representative TMDCs, such as MoS2, WS2, and MoSe2, under femtosecond laser excitation to determine their feasibility as ultrafast photonic devices. It is a combination of experimental Z-scan and time-resolved pump-probe spectroscopy, supported by numerical carrier-dynamics modeling. The maximum values of measured third-order nonlinear susceptibility are of order 10-19 to 10-18 m2/V2, and nonlinear absorption coefficient values are observed at 1550 nm -800 nm, 10-7 m/W. The carrier relaxation times, derived from pump-probe analysis, range from 0.4 to 2.3 ps, indicating the rapid response time of these materials. Saturable absorption modulation depths of up to 18 and optical disease limits at 0.5 GW/cm2 further demonstrate their robustness under high-intensity illumination. The findings indicate strong relationships among layer thickness, excitation wavelength, and the magnitude of nonlinear responses. To sum up, the combination of high nonlinearity, recovery times shorter than a picosecond, and demonstrated optical stability makes two-dimensional TMDCs highly competitive as ultrafast laser sources, optical modulators, and all-optical signal processing systems, with significant prospects for next-generation photonic integration.