Label-free and nondestructive mid-infrared (MIR) vibrational hyperspectral imaging has emerged as a valuable ex-vivo tool for biomedical tissue analysis. However, due to the chemically complex and heterogeneous composition of tissue specimens, the analytical performance of conventional MIR spectral histopathology is limited. We introduce an innovative MIR spectrochemical tissue imaging modality that uses plasmonic metasurfaces to support strong surface-localized electromagnetic fields, enabling the capture of quantitative molecular maps of large-area brain tissue sections. Our surface-enhanced chemical imaging method has broad potential applications in both translational biomedical research and diagnostic clinical histopathology.
Materials with large optical anisotropy are sought after for polarization control, nonlinear phase matching, the realization of unconventional surface waves, among other applications in classical and quantum optics. Here, we demonstrate a bulk uniaxial crystal with atomic-scale structural modulations, Sr9/8TiS3, has a record birefringence Δn = 2.1 across a broad transparent window in the mid- to far-infrared. The excess Sr atoms, compared to stoichiometric SrTiS3, introduce additional electrons into TiS6 octahedral blocks to form highly polarizable clouds, which selectively boost the extraordinary refractive index. Structural modulation is a new tool for the engineering of refractive-index and anisotropy of quantum materials.
We previously demonstrated that the insulator-to-metal transition (IMT) temperature of vanadium dioxide (VO2) can be modified by engineering its defect density via ion implantation. Here, we quantitatively characterize the defect-induced changes to the IMT temperature and optical refractive indices with respect to the ion fluence. We identify an ion-fluence regime in which the IMT temperature can be modified without changes to the optical contrast between the pure phases, which is generally favorable for reconfigurable photonic applications. As a demonstration, we were able to lower the triggering temperature of a VO2-based optical limiter by 18 °C without trading off its transmittance contrast.
Knowledge of temperature-dependent optical properties of materials is required for photonics applications in extreme conditions, i.e., at high temperatures. In this talk, we will describe our latest measurements of temperature-dependent optical properties of materials (oxides, nitrides, semiconductors) for the development of metasurfaces for high-temperature applications that include thermal radiators and light sails. We use oscillator-based models to fit ellipsometry data at different temperatures in the wavelength region where a precise measurement can be made, and extrapolate to get broadband temperature-dependent optical properties. We also demonstrate using simulations how metasurface performance is affected by the temperature-dependence of constituent materials.
Birefringence is a fundamental optical property of anisotropic materials where the refractive index depends on the polarization of light, and is an essential property for devices such as waveplates and polarizers. In 2018, we reported barium titanium sulfide (BaTiS3) to have a broadband birefringence of 0.76 spanning the mid-to-far-infrared range, exhibiting the largest in-plane birefringence of any known bulk materials. In this talk, we will present the characterization of giant birefringence of two more engineered A1+xBX3 crystals, strontium titanium sulfide (Sr1+xTiS3) and barium titanium selenide (BaTiSe3). Our characterization combines polarization-resolved infrared spectroscopy with generalized ellipsometry to extract the optical properties.
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