We have investigated the performance of VO2 microbolometers biased on the semiconducting-metal ph... more We have investigated the performance of VO2 microbolometers biased on the semiconducting-metal phase transition with negative electrothermal feedback. We deposited crystalline thin films of phase-pure VO2, patterned these films into useful test structures, and evaluated the electrical and optical properties relevant to improved uncooled bolometric sensors. A novel ac-biasing method allows for biasing of the devices on the hysteretic semiconducting-metallic
We demonstrate that a new type of structured-illumination imaging may be migrated from the optica... more We demonstrate that a new type of structured-illumination imaging may be migrated from the optical to the terahertz domain. This Fourier-basis technique involves illuminating a target with rapidly moving sinusoidal fringes of controllable spatial frequency and orientation, while measuring the scattered radiation on a single fast detector. This initial proof-of-concept demonstration is purely one-dimensional since the fringe orientation is fixed, but the technique is readily extensible to two dimensions. The fringes are first generated in the near-infrared (808 nm) by passing a high-power laser beam through an acousto-optic Bragg cell driven by a superposition of two RF signals slightly offset in frequency, blocking the undeflected beam, and refocusing the two diffracted beams onto a metal-backed semiconductor wafer. The laser can be amplitude modulated to slow down the moving fringes to accommodate the semiconductor’s temporal response. The semiconductor acts as an optically addressed spatiotemporal modulator for a THz beam illuminating the same area. The periodic optical fringes effectively transform the semiconductor into a reflective THz diffraction grating with a programmable period. The diffracted THz radiation is then imaged onto the remote target plane, where the diffraction orders interfere pairwise to create traveling THz fringes. Scattered radiation from the target is collected by a simple receiver operating in “light bucket” mode, which produces an output signal consisting of a superposition of sinusoidal tones, one for each spatial Fourier component of the target. We present measurements of the THz fringe projector’s performance and compare with a model of the semiconductor modulator’s operation. Finally, we present Fourier-reconstructed images of pairs of point targets as an initial demonstration of THz Fourier-basis agile structured illumination sensing imaging.
Summary form only given. We present a frequency-domain system used for characterizing the scatter... more Summary form only given. We present a frequency-domain system used for characterizing the scatter from arbitrary samples in the frequency range of 220-500 GHz. This system uses a vector network analyzer along with quasi-optical beam shaping components and frequency converters to illuminate and capture scatter radiation providing nominal dynamic range of 90 dB over the 220-325 GHz and 70 dB over the 325-500 GHz band. High-precision motion control of source and receiver, as well as, precision optical alignment techniques allow detailed characterization of scattered electric field and phase from samples. Precision motion control and carefully designed sample mounting allow for a large part of the four-dimensional bi-directional reflectance distribution function (BRDF) of a sample to be accessed. Measurements over a bi-static angle ranging from 205° to 24° with an angular resolution of 0.002° can be made, including mono-static scattering. Out-of-plane angle can be adjusted over the range of +/-5° at 0.5° increments to increase sample BRDF coverage. Data collected from this system is used to generate a zoology of scattering phenomenology from real world and canonical samples. Samples with designed deterministic as well as non-deterministic surface topology statistics were used to both validate this system and to further develop scattering models at millimeter and THz frequencies. The results of an inter-comparison with an analogous time-domain (TD) system developed by NIST in Gaithersburg will be presented. System design and performance details as well as sample data which are compared to both scattering models and the TD system in Gaithersburg will be presented. Examples of different applications for such a system are also presented.
We describe packaging challenges for the development of practical THz imagers based on InP transi... more We describe packaging challenges for the development of practical THz imagers based on InP transistor circuits. Very high aspect ratio (>20:1) die singulation and additive manufacturing for waveguide housings are shown to help in addressing these challenges.
We have investigated the performance of VO2 microbolometers biased on the semiconducting-metal ph... more We have investigated the performance of VO2 microbolometers biased on the semiconducting-metal phase transition with negative electrothermal feedback. We deposited crystalline thin films of phase-pure VO2, patterned these films into useful test structures, and evaluated the electrical and optical properties relevant to improved uncooled bolometric sensors. A novel ac-biasing method allows for biasing of the devices on the hysteretic semiconducting-metallic
We demonstrate that a new type of structured-illumination imaging may be migrated from the optica... more We demonstrate that a new type of structured-illumination imaging may be migrated from the optical to the terahertz domain. This Fourier-basis technique involves illuminating a target with rapidly moving sinusoidal fringes of controllable spatial frequency and orientation, while measuring the scattered radiation on a single fast detector. This initial proof-of-concept demonstration is purely one-dimensional since the fringe orientation is fixed, but the technique is readily extensible to two dimensions. The fringes are first generated in the near-infrared (808 nm) by passing a high-power laser beam through an acousto-optic Bragg cell driven by a superposition of two RF signals slightly offset in frequency, blocking the undeflected beam, and refocusing the two diffracted beams onto a metal-backed semiconductor wafer. The laser can be amplitude modulated to slow down the moving fringes to accommodate the semiconductor’s temporal response. The semiconductor acts as an optically addressed spatiotemporal modulator for a THz beam illuminating the same area. The periodic optical fringes effectively transform the semiconductor into a reflective THz diffraction grating with a programmable period. The diffracted THz radiation is then imaged onto the remote target plane, where the diffraction orders interfere pairwise to create traveling THz fringes. Scattered radiation from the target is collected by a simple receiver operating in “light bucket” mode, which produces an output signal consisting of a superposition of sinusoidal tones, one for each spatial Fourier component of the target. We present measurements of the THz fringe projector’s performance and compare with a model of the semiconductor modulator’s operation. Finally, we present Fourier-reconstructed images of pairs of point targets as an initial demonstration of THz Fourier-basis agile structured illumination sensing imaging.
Summary form only given. We present a frequency-domain system used for characterizing the scatter... more Summary form only given. We present a frequency-domain system used for characterizing the scatter from arbitrary samples in the frequency range of 220-500 GHz. This system uses a vector network analyzer along with quasi-optical beam shaping components and frequency converters to illuminate and capture scatter radiation providing nominal dynamic range of 90 dB over the 220-325 GHz and 70 dB over the 325-500 GHz band. High-precision motion control of source and receiver, as well as, precision optical alignment techniques allow detailed characterization of scattered electric field and phase from samples. Precision motion control and carefully designed sample mounting allow for a large part of the four-dimensional bi-directional reflectance distribution function (BRDF) of a sample to be accessed. Measurements over a bi-static angle ranging from 205° to 24° with an angular resolution of 0.002° can be made, including mono-static scattering. Out-of-plane angle can be adjusted over the range of +/-5° at 0.5° increments to increase sample BRDF coverage. Data collected from this system is used to generate a zoology of scattering phenomenology from real world and canonical samples. Samples with designed deterministic as well as non-deterministic surface topology statistics were used to both validate this system and to further develop scattering models at millimeter and THz frequencies. The results of an inter-comparison with an analogous time-domain (TD) system developed by NIST in Gaithersburg will be presented. System design and performance details as well as sample data which are compared to both scattering models and the TD system in Gaithersburg will be presented. Examples of different applications for such a system are also presented.
We describe packaging challenges for the development of practical THz imagers based on InP transi... more We describe packaging challenges for the development of practical THz imagers based on InP transistor circuits. Very high aspect ratio (>20:1) die singulation and additive manufacturing for waveguide housings are shown to help in addressing these challenges.
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Papers by erich grossman