Jeffrey Geldmeier | Searcharxiv

arXiv2023

Wide Field-of-View, Large-Area Long-wave Infrared Silicon Metalenses

Long-wave infrared (LWIR, 8-12 $\mu m$ wavelengths) is a spectral band of vital importance to thermal imaging. Conventional LWIR optics made from single-crystalline Ge and chalcogenide glasses are bulky and fragile. The challenge is exacerbated for wide field-of-view (FOV) optics, which traditionally mandates multiple cascaded elements that severely add to complexity and cost. Here we designed and experimentally realized a LWIR metalens platform based on bulk Si wafers featuring 140$^\circ$ FOV. The metalenses, which have diameters exceeding 4 cm, were fabricated using a scalable wafer-level process involving photolithography and deep reactive ion etching. Using a metalens-integrated focal plane array, we further demonstrated wide-angle thermal imaging.

physics.optics↗

arXiv2018

Plasmonic Aerosols

Plasmonic nanoparticles resonantly couple to and confine light below the diffraction limit. This mechanism has enabled a modern renaissance in optical materials, with potential applications ranging from sensing and circuitry to renewable energies and medicines. However, these plasmonic materials are typically constrained to dilute liquids or solid two-dimensional surfaces, thereby limiting their possibilities. Here, we experimentally demonstrate a plasmonic aerosol by transitioning liquid suspensions of gold nanorods into the gas phase and simultaneously measuring their optical spectra. By measuring and modeling the evolution of the longitudinal absorbance peak of the nanorods from the liquid to the gas phase, we find that the aerosols are optically homogeneous and thermodynamically stable. We show that by tailoring the aspect ratio of the nanorods, the aerosol absorbance peak is tunable from visible to mid-wave infrared wavelengths. We find the sensitivity of the absorbance peak wavelength to changes in the refractive index of the gas depends linearly on the aspect ratio and can be estimated from the geometric and material properties of the nanorod. For high aspect ratio nanorods the sensitivity becomes extremely large, which may be useful in aiding geoengineering challenges. This work establishes plasmonic aerosols, potentially enabling exciting opportunities for fundamental and applied research.

physics.optics↗