Publications & Presentations

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.

Laser-Based Sensors for Addressing Climate Change

Mickey B. Frish
Conference on Lasers and Electro-Optics (CLEO)
Session AM3B: Greenhouse Gas Sensing
May 15, 2017, San Jose, CA

Identifying, measuring, and reducing mankind’s contribution to climate change is an
urgent international endeavor. This paper describes our work dedicated towards developing and
applying laser sensors to support efforts to reduce greenhouse gas emissions.