Publications & Presentations

High-efficiency thermophotovoltaic energy conversion enabled by a metamaterial selective emitter

High-efficiency thermophotovoltaic energy conversion enabled by a metamaterial selective emitter
DAVID N. WOOLF, EMIL A. KADLEC, DON BETHKE, ALBERT D. GRINE, JOHN J. NOGAN, JEFFREY G. CEDERBERG, D. BRUCE BURCKEL, TING SHAN LUK, ERIC A. SHANER, and JOEL M. HENSLEY
Optica Vol. 5, Issue 2, pp. 213-218 (2018) •https://doi.org/10.1364/OPTICA.5.000213

Thermophotovoltaics (TPV) is the process by which photons radiated from a thermal emitter are converted into electrical power via a photovoltaic cell.

Selective thermal emitters that can survive at temperatures at or above ∼1000°C have the potential to greatly improve the efficiency of TPV energy conversion by restricting the emission of photons with energies below the photovoltaic (PV) cell bandgap energy. In this work, we demonstrated TPV energy conversion using a high-temperature selective emitter, dielectric filter, and 0.6 eV In0.68Ga0.32As photovoltaic cell. We fabricated a passivated platinum and alumina frequency-selective surface by conventional stepper lithography. To our knowledge, this is the first demonstration of TPV energy conversion using a metamaterial emitter. The emitter was heated to >1000°C, and converted electrical power was measured. After accounting for geometry, we demonstrated a thermal-to-electrical power conversion efficiency of 24.1  0.9% at 1055°C. We separately modeled our system consisting of a selective emitter, dielectric filter, and PV cell and found agreement with our measured efficiency and power to within 1%. Our results indicate that high-efficiency TPV generators are possible and are candidates for remote
power generation, combined heat and power, and heat-scavenging applications.

Spatially resolved modeling and measurements of metastable argon atoms in argon-helium microplasmas

Alan R. Hoskinson, José Gregório, Jeffrey Hopwood, Kristin L. Galbally-Kinney, Steven J. Davis, and Wilson T. Rawlins
Journal of Applied Physics 121, 153302 (2017); https://doi.org/10.1063/1.4981922

Microwave-driven plasmas operating near atmospheric pressure have been shown to be a promising technique for producing the high density of argon metastable atoms required for optically pumped rare gas laser systems. Stable microwave-driven plasmas can be generated at high pressures using microstrip-based resonator circuits.

We present results from computational modeling and laser absorption measurements of argon metastable densities in such plasmas operating in argon-helium gas mixtures at pressures up to 300 Torr. The model and measurements resolve the plasma characteristics both perpendicular to the substrate surface and along the resonator length. The measurements qualitatively and in many aspects quantitatively confirm the accuracy of the model. The plasmas exhibit distinct behaviors depending on whether the operating gas is mostly argon or mostly helium. In high-argon plasmas, the metastable density has a large peak value but is confined very closely to the electrode surfaces as well as being reduced near the discharge gap itself. In contrast, metastable densities in high helium-fraction mixtures extend through most of the plasma. In all systems, increasing the power extends the region of metastable along the resonator length, while the extent away from the substrate surface remains approximately constant.

Investigation of tissue cellularity at the tip of the core biopsy needle with optical coherence tomography

NICUSOR IFTIMIA, JESUNG PARK, GOPI MAGULURI, SAVITRI KRISHNAMURTHY, AMANDA MCWATTERS, AND SHARJEEL H. SABIR3 "Investigation of tissue cellularity at the tip of the core biopsy needle with optical coherence tomography", Vol. 9. No. 2 1 Feb 2018. Biomedical Optics Express 694-704.
We report the development and the pre-clinical testing of a new technology based on optical coherence tomography (OCT) for investigating tissue composition at the tip of the core biopsy needle.
While ultrasound, computed tomography, and magnetic resonance imaging are routinely used to guide needle placement within a tumor, they still do not provide the resolution needed to investigate tissue cellularity (ratio between viable tumor and benign stroma) at the needle tip prior to taking a biopsy core. High resolution OCT imaging, however, can be used to investigate tissue morphology at the micron scale, and thus to determine if the biopsy core would likely have the expected composition. Therefore, we implemented this capability within a custom-made biopsy gun and evaluated its capability for a correct estimation of tumor tissue cellularity. A pilot study on a rabbit model of soft tissue cancer has shown the capability of this technique to provide correct evaluation of tumor tissue cellularity in over 85% of the cases. These initial results indicate the potential benefit of the OCT-based approach for improving the success of the core biopsy procedures.

Progress in Standoff Surface Contaminant Detector Platform

Julia R. Dupuis, Jay Giblin, John Dixon, Joel Hensley, David Mansur, and William J. Marinelli
SPIE Defense and Security
Micro- and Nanotechnology Sensors, Systems, and Applications IX
Anaheim, CA, April 13, 2017

Progress towards the development of a longwave infrared quantum cascade laser (QLC) based standoff surface contaminant detection platform is presented. The detection platform utilizes reflectance spectroscopy with application to optically thick and thin materials including solid and liquid phase chemical warfare agents, toxic industrial chemicals and materials, and explosives.

The platform employs an ensemble of broadband QCLs with a spectrally selective detector to interrogate target surfaces at 10s of m standoff. A version of the Adaptive Cosine Estimator (ACE) featuring class based screening is used for detection and discrimination in high clutter environments. Detection limits approaching 0.1 μg/cm2 are projected through speckle reduction methods enabling detector noise limited performance.

The design, build, and validation of a breadboard version of the QCL-based surface contaminant detector are discussed. Functional test results specific to the QCL illuminator are presented with specific emphasis on speckle reduction.

Progress in Standoff Surface Contaminant Detector Platform

Julia R. Dupuis, Jay Giblin, John Dixon, Joel Hensley, David Mansur, and William J. Marinelli
SPIE Defense and Commercial Sensing,
Anaheim, CA, April 9-13, 2017

Progress towards the development of a longwave infrared quantum cascade laser (QLC) based standoff surface contaminant detection platform is presented. The detection platform utilizes reflectance spectroscopy with application to optically thick and thin materials including solid and liquid phase chemical warfare agents, toxic industrial chemicals and materials, and explosives.

The platform employs an ensemble of broadband QCLs with a spectrally selective detector to interrogate target surfaces at 10s of m standoff. A version of the Adaptive Cosine Estimator (ACE) featuring class based screening is used for detection and discrimination in high clutter environments. Detection limits approaching 0.1 ug/cm2 are projected through speckle reduction methods enabling detector noise limited performance.

The design, build, and validation of a breadboard version of the QCL-based surface contaminant detector are discussed. Functional test results specific to the QCL illuminator are presented with specific emphasis on speckle reduction.