Theoretical Demonstration of the Interest of Using Porous Germanium to Fabricate Multilayer Vertical Optical Structures for the Detection of SF6 Gas in the Mid-Infrared

Volume detection based on porous silicon waveguide for CO2 mid-infrared spectroscopy

A mid-infrared (mid-IR) porous silicon (PSi) waveguide gas sensor was fabricated. PSi guiding and confinement layers were prepared by electrochemical anodization. Ridge waveguides were patterned using standard i-line photolithography and reactive ion etching. Due to the open pores, light and gas molecules interact in the inside volume, unlike bulk material in which the interaction takes place with the evanescent part of the light. Propagation losses are measured for a wavelength range spanning from λ = 3.9 to 4.55 µm with a value of 11.4 dB/cm at λ = 4.28 µm. The influence of native oxidation and ageing on the propagation losses was investigated. Limit of detection (LoD) of 1000 ppm is obtained with the waveguide sensor at the carbon dioxide (CO2) absorption peak at λ = 4.28 µm.

Low Solar Absorptance, High Emittance Performance Thermochromic VO2-Based Smart Radiator Device

Thermochromic vanadium dioxide (VO₂)-based smart radiator devices (SRDs) display emittance variation with changes in temperature, making them very promising for energy-efficient thermal control of spacecrafts in general, and nanosatellites in particular. However, the high solar absorptance of the VO₂-based SRDs remains too high for their intended application. Based on an approach combining optical simulation and experimental work, I demonstrate that an additional top stack layer alternating between high and low refractive indices made of a-Si(25 nm)/SiO₂(67 nm) reduces the solar absorptance of a VO₂-based SRD by 35% (from 0.43 to 0.28) while keeping the emittance performance of the SRD within the requirements for the intended application (low-temperature emittance εL = 0.35, high-temperature emittance εH = 0.81 and emittance tuneability with temperature Δε = 0.46). I also discuss factors to consider while designing additional top stack layers alternating between high and low refractive indices to further decrease the SRD's solar absorptance without affecting its emittance performance.