Giant Modulation of Refractive Index from Picoscale Atomic Displacements.

It is shown that structural disorder-in the form of anisotropic, picoscale atomic displacements-modulates the refractive index tensor and results in the giant optical anisotropy observed in BaTiS, a quasi-1D hexagonal chalcogenide. Single-crystal X-ray diffraction studies reveal the presence of antipolar displacements of Ti atoms within adjacent TiS chains along the c-axis, and threefold degenerate Ti displacements in the a-b plane. Ti solid-state NMR provides additional evidence for those Ti displacements in the form of a three-horned NMR lineshape resulting from a low symmetry local environment around Ti atoms.

Colossal Optical Anisotropy from Atomic-Scale Modulations.

Materials with large birefringence (Δn, where n is the refractive index) are sought after for polarization control (e.g., in wave plates, polarizing beam splitters, etc.

Metasurface-Enhanced Mid-Infrared Spectrochemical Imaging of Tissues.

Label-free and nondestructive mid-infrared vibrational hyperspectral imaging is an essential tissue analysis tool, providing spatially resolved biochemical information critical to understanding physiological and pathological processes. However, the chemically complex and spatially heterogeneous composition of tissue specimens and the inherently weak interaction of infrared light with biomolecules limit the analytical performance of infrared absorption spectroscopy. Here, an advanced mid-infrared spectrochemical tissue imaging modality is introduced using metasurfaces that support strong surface-localized electromagnetic fields to capture quantitative molecular maps of large-area murine brain tissue sections.

Correcting thermal-emission-induced detector saturation in infrared spectroscopy.

We found that temperature-dependent infrared spectroscopy measurements (i.e., reflectance or transmittance) using a Fourier-transform spectrometer can have substantial errors, especially for elevated sample temperatures and collection using an objective lens.

Tuning carrier density and phase transitions in oxide semiconductors using focused ion beams.

We demonstrate spatial modification of the optical properties of thin-film metal oxides, zinc oxide (ZnO) and vanadium dioxide (VO) as representatives, using a commercial focused ion beam (FIB) system. Using a Ga FIB and thermal annealing, we demonstrated variable doping of a wide-bandgap semiconductor, ZnO, achieving carrier concentrations from 10 cm to 10 cm. Using the same FIB without subsequent thermal annealing, we defect-engineered a correlated semiconductor, VO, locally modifying its insulator-to-metal transition (IMT) temperature by up to ∼25 °C.

Coiled Optical Nanofiber for Optofluidic Absorbance Detection.

A challenge for optofluidic absorbance detection is the high concentration limit of detection due to the short optical path length. Herein, we introduce a concept of utilizing the coiled optical nanofiber for highly sensitive and robust optofluidic absorbance detection. Investigated by measuring the absorbance of FeCl solutions, the sensor shows a detection limit down to 10 μM with excellent reversibility in a concentration range of 0-5 mM.