Gary H. Bernstein

We are developing circular-polarization-sensitive infrared detectors called spiral thermoelectrically coupled nanoantennas (TECNAs) for solar imaging and terrestrial sensing applications. In a spiral TECNA, a nanoscale thermocouple is used to measure the localized joule heating caused by induced currents within a spiral nanoantenna structure. This paper discusses the response of spiral TECNAs to elliptical polarization, which must be considered when performing circular polarization measurements of sources of arbitrary polarization. Measurements and simulations show that spiral TECNAs respond maximally to a specific matching elliptical polarization and minimally to the orthogonal, nonmatching elliptical polarization. Given that any polarization can be decomposed into these two basis polarizations, we find that the spiral-TECNA response to an arbitrary polarization scales with the matching-elliptical-polarization component. The spiral TECNA polarization response is analogous to that of RF spiral antennas, despite the intermediate transduction between high-frequency currents and heat.

This work studies the surface morphology and roughness differences of Si surfaces etched by XeF2 under pulsed and continuous flow conditions. During pulsed etch, XeF2 is introduced into the processing chamber in discrete doses. The sample is exposed to the fixed supply of etchant for a set duration. In contrast, during a continuous flow etch, a steady supply of XeF2 gas maintains a stable etchant concentration in the process chamber. Comparable etch rates and etch depths were attained while ensuring that both pulsed and continuous flow etching were conducted under similar chamber pressures and loading. Although the overall root-mean-square (RMS) roughness values for the continuous and pulsed etch were similar, 0.134 and 0.135 μm, respectively, significant differences in the surface morphology were observed. Laser scanning confocal microscopy, SEM imaging, and FIB cross sections of the etched surfaces revealed pronounced differences in the spatial frequency components of the surface textures. Continuous flow etching produced surfaces with sharper features and higher spatial frequency components. These results indicate that the etching methodology influences Si surface characteristics even when etch depths and rates remain constant.

We present thermoelectrically coupled nanoantennas (TECNAs) with log-spiral antennas for mid- and long-wave infrared detection. The nanoantenna resonantly absorbs the incident IR radiation and, due to its shape, provides selectivity for circular polarization. We used HFSS simulations to design TECNAs with both left- and right-handed antennas and show the effect of each design parameter of the spiral on the response of the devices. The fabricated devices were characterized at 10.6 μm wavelength, and the measurement results show that the response is about five times larger when the polarization handedness of the incident IR radiation matches to the antenna

We are studying thermoelectrically coupled nanoantennas, referred to as TECNAs, to determine the angle of incidence of laser beams in the long-wave IR regime. TECNAs consist of a nanoantenna and a nanothermocouple that are fabricated over a quasi-spherical cavity etched into the Si substrate. The antenna nature of the TECNAs makes them polarization- and wavelength-selective, and the cavity provides directional selectivity. In this paper, we experimentally demonstrate that the far-field radiation pattern of TECNAs is altered by positioning them at various locations above the cavity. Both experimental results and finite element method simulations show that the resulting radiation pattern of the antenna is determined by the nanoantenna’s position relative to the center of the cavity. Additionally, we highlight that the substrate significantly affects the far-field pattern of TECNAs; under coherent excitation, interference patterns overlay the radiation pattern due to back reflection from the substrate. We have shown that this effect is attributed to the substrate, as the interference pattern is negligible under incoherent illumination.

This work investigates the speed and responsivity of thermoelectrically coupled nanoantennas (TECNAs) in vacuum. TECNAs are long-wave infrared (IR) detectors that absorb electromagnetic radiation via a resonant dipole antenna. Joule heating within the antenna is converted to a voltage via a nanoscale thermocouple (NTC). Heat loss due to air is reduced under vacuum, allowing for improved device responsivity, but at the expense of speed. A finite difference model is introduced that calculates the steady-state and transient thermal transport within various TECNA designs across a range of ambient pressures. The modeled pressure dependence was derived from nanoscale convection coefficients found in the literature. Models were experimentally verified by studying the pressure-dependent and frequency-dependent voltage response of TECNAs exposed to modulated 10.6 μm IR radiation. Improvements in responsivity ranging from 3 to 4.5 times were demonstrated between atmosphere and vacuum, with 90% of improvement occurring between atmospheric pressure and 1 Torr (rough vacuum) in each design. Devices exhibited bandwidths of at least 10 kHz (roughly 100 times faster than common microbolometers) under vacuum with negligible signal attenuation, though future work is needed to fully characterize device frequency response.

The paper presents a design-oriented analysis of a dipole nanoantenna suspended above a cavity. A thermocouple junction resolves the temperature of the antenna. The low thermal inertia of the device and low noise provide a high potential for high detectivity. Experimental results are compared to the model.

SPIE Digital Library Proceedings

Transneptunian objects (TNOs) are a source of invaluable information to access the history and evolution of the outer solar system. However, observing these faint objects is a difficult task. As a consequence, important properties such as size and albedo are known for only a small fraction of them. Now, with the results from deep sky surveys and the Gaia space mission, a new exciting era is within reach as accurate predictions of stellar occultations by numerous distant small solar system bodies become available. From them, diameters with kilometer accuracies can be determined. Albedos, in turn, can be obtained from diameters and absolute magnitudes. We use observations from the Dark Energy Survey (DES) from November 2012 until February 2016, amounting to 4292847 CCD frames. We searched them for all known small solar system bodies and recovered a total of 202 TNOs and Centaurs, 63 of which have been discovered by the DES collaboration until the date of this writing. Their positions were determined using the Gaia Data Release 2 as reference and their orbits were refined. Stellar occultations were then predicted using these refined orbits plus stellar positions from Gaia. These predictions are maintained, and updated, in a dedicated web service. The techniques developed here are also part of an ambitious preparation to use the data from the Large Synoptic Survey Telescope (LSST), that expects to obtain accurate positions and multifilter photometry for tens of thousands of TNOs.