Noninvasive Modulation of In-Plane Optical Anisotropy in ReSe₂ via Etching-Induced Strain

The modulation of in-plane optical anisotropy in two-dimensional (2D) materials is of great significance for both fundamental research and optoelectronic device engineering. Here, we present a nondestructive and spatially tunable approach to control the anisotropic optical response of ReSe2 through substrate etching–induced dielectric perturbations. Using a customized reflection difference spectroscopy (RDS) imaging system, we noninvasively characterized ReSe2 flakes transferred onto both etched and pristine regions of patterned SiO2 substrates. The etching process generates localized stress fields that weaken the intrinsic in-plane anisotropy of ReSe2, enhance its overall reflectance, and induce a slight rotation of its optical principal axis. These effects are attributed to strain-driven modifications of the dielectric environment, which alter the optical response without compromising the structural integrity of the flakes. Our findings demonstrate that substrate-induced strain provides an effective means for controllable, localized, and nondestructive modulation of optical anisotropy in 2D semiconductors. This work establishes a practical strategy for tailoring the anisotropic optical properties of layered materials, offering potential implications for the design of strain-engineered optoelectronic devices and polarization-sensitive applications.