Advanced optical indicators based on functional metastructure for thermoelastic optical indicator microscope

초록

This study presents advanced optical indicators (OIs) based on functional metastructures (MSs) for thermoelastic optical indicator microscopy (TEOIM). The proposed MS-based OIs are designed to enhance microwave-induced thermoelastic response through geometry-controlled electromagnetic (EM) coupling, overcoming the limited sensitivity and isotropic behavior of conventional homogeneous indium tin oxide (ITO) indicators. By combining finite element simulations with experimental validation, we demonstrate that MS-based OIs provide significantly higher sensitivity and enable directional (anisotropic) detection of in-plane EM field components. Among the investigated designs, specific MSs exhibit either a strong isotropic thermal response or pronounced anisotropy, enabling selective visualization of vertical and horizontal field components. The effective spatial resolution of TEOIM is governed by thermoelastic stress distribution and optical readout rather than by the microwave wavelength, yielding an estimated resolution of approximately 150-250 nm under visible-light illumination. While the simulations employ simplified thermal boundary conditions and are intended to capture relative trends rather than absolute temperature values, the experimental results consistently confirm the enhanced sensitivity and directional selectivity introduced by MS geometry. These findings highlight the potential of MS-based OIs to improve microwave near-field visualization for metamaterial characterization, advanced sensor development, and biomedical sensing.

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