ALL-DIELECTRIC METASURFACE THERMAL EMITTERS FOR MID-IR SPECTROSCOPY

Abstract

A thermal emitter using a metasurface to tailor the emission spectrum in the mid-infrared for gas-sensing applications is demonstrated. The design consists of an array of high index dielectric elliptical pucks above a metal back-reflector. Using full-wave simulations in HFSS (Ver. 19.0.0), it has been shown that the achievable Q-factor (Q ≈ 150) in this structure is an order of magnitude larger than in plasmonic arrays (Q ≈ 16), attributed to the low-loss in the dielectric materials. Furthermore, the thermal emission properties of the structure can be engineered by manipulating the geometry of the unit cell, and these unit cells can provide polarized thermal emission simultaneously in two separate frequency bands determined by the ellipticity parameter of the puck. Design of the thermal emitter requires accurate knowledge of frequency dependent optical constants of specific deposited materials in the mid-infrared region. Optical parameters for thin film Silicon and Silicon Dioxide deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) are not readily available in the literature. These parameters were measured and used in simulation of the thermal emitter with a resonant frequency corresponding to the absorption spectra of a known industrial gas Sulphur Dioxide (SO2). The narrow-band thermal emitter was fabricated in the Carleton University Micro Fabrication Facility and tested for thermal emissivity. Measured emissivity was found to match simulation when variations in the resonator structure due to process variation were taken into account.