Publications & Presentations

Active standoff chemical identification detector

Active standoff chemical identification detector
Jay P. Giblin*, Julia R. Dupuis, John P. Dixon, Joel M. Hensley, David J. Mansur, and William J. Marinelli
SPIE Defense and Commercial Sensing, Orlando, FL, 15 - 19 April 2018

An active, standoff, all-phase chemical detection capability has been developed under IARPA’s SILMARILS program. The detection platform utilizes reflectance spectroscopy in the longwave infrared coupled with an automated detection algorithm that implements physics-based reflectance models for planar chemical films, particulate in the solid and liquid phase, and vapors.

Target chemicals include chemical warfare agents, toxic industrial chemicals, and explosives. The platform employs broadband Fabry-Perot quantum cascade lasers with a spectrally selective detector to interrogate target surfaces at tens of meter standoff. A statistical F-test in a noise whitened space is used for detection and discrimination over a large target spectral library in high clutter environments. The capability is described with an emphasis on the physical reflectance models used to predict spectral reflectivity signatures as a function of surface contaminant presentation and loading. Developmental test results from a breadboard version of the detector platform are presented. Specifically, solid and liquid surface contaminants were detected and identified from a library of 325 compounds down to 30 μg/cm2 surface loading at a 5 m standoff. Vapor detection was demonstrated via topographic backscatter.

Compact Lidar for Continuous Monitoring of Atmospheric Extinction

Compact Lidar for Continuous Monitoring of Atmospheric Extinction
David M. Sonnenfroh*, Robert J. Minelli, Joseph A.K. Goodwin, and W. Terry Rawlins
SPIE Defense and Commercial Sensing, Orlando, FL, 15 - 19 April 2018

Physical Sciences Inc. is developing an advanced, compact lidar capable of continuous mapping of atmospheric extinction to provide environmental situational awareness for high energy laser weapon operations by the Navy.

The lidar uses a MicroPulse Lidar architecture and combines a solid state Nd:YLF laser operating at 1 micron with photon counting detectors and advanced aerosol retrieval algorithms. We report on the design of the engineering prototype and provide a summary of the system performance demonstrated during the Comprehensive Atmospheric Boundary Layer Extinction / Turbulence Refinement eXperiment conducted at the Shuttle Landing Facility at Kennedy Space Center in June, 2017.

Standoff Detection from Diffusely Scattering Surfaces using Dual Quantum Cascade Laser Comb Spectroscopy

Standoff Detection from Diffusely Scattering Surfaces using Dual Quantum Cascade Laser Comb Spectroscopy
Joel M. Hensley, Justin M. Brown, Mark G. Allen, Markus Geiser, Pitt Allmendinger, Markus Mangold, Andreas Hugi, Pierre Jouy, and Jérôme Faist
SPIE Defense + Commercial Sensing Conference, Orlando, FL, April 15-19, 2018

Designed dispersion compensated quantum cascade OFC sources at 8 and 10mm

At 8mm demonstrated ~1W cw average power (per laser) at room temperature with comb ~80 cm-1 comb width

Demonstrated surface mass loading sensitivity of few mg/cm2 at standoff distances of 0.3 and 1 meter from diffuse surfaces

Primary improvement needed: increased bandwidth
–150 cm-1 possible with improve dispersion control
–beyond 150 cm-1, will also require faster detectors or better matching between individual comb spacing

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

High-efficiency thermophotovoltaic energy conversion enabled by a metamaterial selective emitter
Optica Vol. 5, Issue 2, pp. 213-218 (2018) •

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);

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.