arXiv subjects

Jin-Woo Cho

Publications and source records attributed to Jin-Woo Cho.

5 recordsLinked to original sources

arXiv2026

Anti-reflection coatings for highly anisotropic materials in the mid infrared

We develop and optimize thin anti-reflection coatings (ARCs) for highly anisotropic materials in the mid infrared. Unlike conventional ARCs that assume nearly isotropic refractive indices, this work fully integrates the anisotropic nature of materials into the design process. We describe two designs of thin ARCs for highly anisotropic materials: a single form-birefringent layer, and a planar bilayer. We realized the planar bilayer ARC experimentally, demonstrating excellent mid-infrared anti-reflectance across over a broad range of angles for all polarizations.

physics.optics↗

arXiv2026

Material selection for mid-infrared thin-film coatings and windows

We summarized the room-temperature optical properties for infrared-transparent materials, defining transparency windows for two different applications: thin-film coatings (absorption coefficient $α< 10 cm^{-1}$) and windows ($α< 1 cm^{-1}$). The transparency requirements for thin films are substantially less stringent, enabling the use of many more optical materials for a given wavelength range. To make an easy-to-use reference, we categorized materials by chemical group, crystallinity, and typical deposition technique, and discussed practical pros and cons such as chemical and thermal stability, mechanical hardness, and cost. The datasets and plotting scripts are provided so that users can regenerate transparency-window maps for different applications. If you do optical design at infrared wavelengths, we recommend that you print out the figures and stick them on your wall.

physics.optics↗

arXiv2025

Preventing overfitting in infrared ellipsometry using temperature dependence: fused silica as a case study

Fitting oscillator models to variable-angle spectroscopic ellipsometry (VASE) data can lead to non-unique, unphysical results. We demonstrate using temperature-dependent trends to prevent overfitting and ensure model physicality. As a case study, we performed mid-infrared VASE measurements on fused silica (SiO2) of various grades, from room temperature to 600 °C. We fitted oscillator models independently at each temperature, and confirmed the model's physical validity by observing the expected monotonic trends in vibrational oscillator parameters. Using this technique, we generated a highly accurate dataset for the temperature-dependent complex refractive index of fused silica for modeling mid-infrared optical components such as thermal emitters.

physics.optics↗

arXiv2025

Passive radiative cooling using temperature-dependent emissivity can sometimes outperform static emitters

In passive sky-facing radiative cooling, wavelength-selective thermal emitters in the atmospheric transparency window of 8-13 $μ$m can reach lower temperatures compared to broadband emitters, but broadband emitters always have higher cooling power when the emitter is warmer than the ambient. Here, we propose a temperature-tunable thermal emitter that switches between a wavelength-selective state -- with high emissivity only in the atmospheric transparency window of 8-13 $μ$m -- and a broadband-emissive state with high emissivity in the 3-25 $μ$m range, thus maintaining high cooling potential across all temperatures. We also propose a realization of such a temperature-tunable emitter using the phase transition of vanadium dioxide (VO$_2$), which can be tuned to the ambient temperature using a combination of doping and defect engineering.

physics.optics↗

arXiv2025

Dynamically Tunable Membrane Metasurfaces for Infrared Spectroscopy

Mid-infrared spectroscopy enables biochemical sensing by identifying vibrational molecular fingerprints, but it faces limitations in instrumentation portability and analytical sensitivity. Optical metasurfaces with strong mid-IR photonic resonances provide an attractive solution towards on-chip spectrometry and sensitive molecular detection, yet their static nature hinders their anticipated impact. Here, we introduce and demonstrate dynamically tunable silicon membrane metasurfaces exhibiting high-Q transmissive resonances in the fingerprint region. By harnessing silicon's thermo-optical properties, we achieve continuous modulation of electromagnetically induced transparency (EIT)-like modes that emerge upon the interference of quasi-bound states in the continuum (q-BICs) and surface lattice modes. We measure a spectral tuning rate of 0.06 $cm^{-1}/K$ by continuously sweeping the sharp EIT resonances over a 23.5 $cm^{-1}$ spectral range across a temperature range of 300-700 K. This dynamic transmission control enables non-contact chemical analysis of polymer films by detecting characteristic absorption bands of polystyrene (1450 and 1492 $cm^{-1}$) and Poly(methyl methacrylate) (1730 $cm^{-1}$) without bulky spectrometers. When analyte molecules fill the metasurface-generated photonic cavities, we demonstrate vibrational strong coupling between the Poly(methyl methacrylate)'s carbonyl band and the EIT mode, manifested in the Rabi splitting of $\sim$ 43 $cm^{-1}$. Our results establish a new photonic platform that unites spectral precision, strong field enhancement, and reconfigurability, offering diverse potential for compact mid-IR spectroscopy, molecular sensing, and programmable polaritonic photonics.

physics.app-ph↗