Vincent J. Riot

Autonomous, broad-spectrum detection of hazardous aerosols in seconds.

Actual or surrogate chemical, biological, radiological, nuclear, and explosive materials and illicit drug precursors can be rapidly detected and identified when in aerosol form by a Single-Particle Aerosol Mass Spectrometry (SPAMS) system. This entails not only the sampling of such particles but also the physical analysis and subsequent data analysis leading to a highly reliable alarm state. SPAMS hardware is briefly reviewed. SPAMS software algorithms are discussed in greater detail. A laboratory experiment involving actual threat and surrogate releases mixed with ambient background aerosols demonstrates broad-spectrum detection within seconds. Data from a field test at the San Francisco International Airport demonstrate extended field operation with an ultralow false alarm rate. Together these data sets demonstrate a significant and important advance in rapid aerosol threat detection.

Space-based telescopes for actionable refinement of ephemeris pathfinder mission

The Space-based Telescopes for Actionable Refinement of Ephemeris (STARE) program will collect the information needed to help satellite operators avoid collisions in space by using a network of nano- satellites to determine more accurate trajectories for selected space objects orbiting the Earth. In the first phase of the STARE program, two pathfinder cube-satellites (CubeSats) equipped with an optical ima- ging payload are being developed and deployed to demonstrate the main elements of the STARE concept. We first give an overview of the STARE program. The details of the optical imaging payload for the STARE pathfinder CubeSats are then described, followed by a description of the track detection algorithm that will be used on the images it acquires. Finally, simulation results that highlight the effectiveness of the mission are presented.

Electro-optical testing of fully depleted CCD image sensors for the Large Synoptic Survey Telescope camera

The LSST Camera science sensor array will incorporate 189 large format Charge Coupled Device (CCD) image sensors. Each CCD will include over 16 million pixels and will be divided into 16 equally sized segments and each segment will be read through a separate output amplifier. The science goals of the project require CCD sensors with state of the art performance in many aspects. The broad survey wavelength coverage requires fully depleted, 100 micrometer thick, high resistivity, bulk silicon as the imager substrate. Image quality requirements place strict limits on the image degradation that may be caused by sensor effects: optical, electronic, and mechanical. In this paper we discuss the design of the prototype sensors, the hardware and software that has been used to perform electro-optic testing of the sensors, and a selection of the results of the testing to date. The architectural features that lead to internal electrostatic fields, the various effects on charge collection and transport that are caused by them, including charge diffusion and redistribution, effects on delivered PSF, and potential impacts on delivered science data quality are addressed.

A Compact, Flexible, High Channel Count DAQ Built From Off-the-Shelf Components

Medium to large channel count detectors are usually faced with a few unattractive options for data acquisition (DAQ). Small to medium-sized TPC experiments, for example, are too small to justify the expense and development time of application specific integrated circuits (ASIC). Commercial rack mounted electronics are too bulky and expensive for large channel counts. The combination of commercial high-speed high-density FPGAs, ADCs, and small discrete components provides another option that scales to tens of thousands of channels and is only slightly larger than ASICs using off-the-shelf components. A working example of this alternative solution is presented.

Detection of biological particles in ambient air using Bio-Aerosol Mass Spectrometry

The Bio-Aerosol Mass Spectrometry (BAMS) system is an instrument used for the real time detection and identification of biological aerosols. Particles are drawn from the atmosphere directly into vacuum and tracked as they scatter light from several continuous wave lasers. After tracking, the fluorescence of individual particles is excited by a pulsed 266nm or 355nm laser. Molecules from those particles with appropriate fluorescence properties are subsequently desorbed and ionized using a pulsed 266nm laser. Resulting ions are analyzed in a dual polarity mass spectrometer. During two field deployments at the San Francisco International Airport, millions of ambient particles were analyzed and a small but significant fraction were found to have fluorescent properties similar to Bacillus spores and vegetative cells. Further separation of non-biological background particles from potential biological particles was accomplished using laser desorption/ionization mass spectrometry. This has been shown to enable some level of species differentiation in specific cases, but the creation and observation of higher mass ions is needed to enable a higher level of specificity across more species. A soft ionization technique, matrix-assisted laser desorption/ionization (MALDI) is being investigated for this purpose. MALDI is particularly well suited for mass analysis of biomolecules since it allows for the generation of molecular ions from large mass compounds that would fragment under normal irradiation. Some of the initial results from a modified BAMS system utilizing this technique are described.

LSST camera optics design

The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, telescope design feeding a camera system that includes a set of broad-band filters and three refractive corrector lenses to produce a flat field at the focal plane with a wide field of view. Optical design of the camera lenses and filters is integrated in with the optical design of telescope mirrors to optimize performance. We discuss the rationale for the LSST camera optics design, describe the methodology for fabricating, coating, mounting and testing the lenses and filters, and present the results of detailed analyses demonstrating that the camera optics will meet their performance goals.

Optical payload for the STARE pathfinder mission

The Space-based Telescopes for Actionable Refinement of Ephemeris (STARE) program will collect the information needed to help satellite operators avoid collisions in space by using a network of nano-satellites to determine more accurate trajectories for selected space objects orbiting the Earth. In the first phase of the STARE program, two pathfinder cube-satellites (CubeSats) equipped with an optical imaging payload are being developed and deployed to demonstrate the main elements of the STARE concept. In this paper, we first give an overview of the STARE program. We then describe the details of the optical imaging payload for the STARE pathfinder CubeSats, including the optical design and the sensor characterization. Finally, we discuss the track detection algorithm that will be used on the images acquired by the payload.

Characterization of ambient aerosols at the San Francisco International Airport using bioaerosol mass spectrometry

The BioAerosol Mass Spectrometry (BAMS) system is a rapidly fieldable, fully autonomous instrument that can perform correlated measurements of multiple orthogonal properties of individual aerosol particles. The BAMS front end uses optical techniques to nondestructively measure a particles aerodynamic diameter and fluorescence properties. Fluorescence can be excited at 266nm or 355nm and is detected in two broad wavelength bands. Individual particles with appropriate size and fluorescence properties can then be analyzed more thoroughly in a dual-polarity time-of-flight mass spectrometer. Over the course of two deployments to the San Francisco International Airport, more than 6.5 million individual aerosol particles were fully analyzed by the system. Analysis of the resulting data has provided a number of important insights relevant to rapid bioaerosol detection, which are described here.

A 4-/spl pi/ field of view Compton imager based on a single planar germanium detector

A Compton imager has been developed based on a single germanium strip detector. The system has the ability to image point or continuous gamma ray sources located anywhere in a 4-/spl pi/ field of view. The effective energy range for imaging is approximately 200 keV to greater than 1 MeV. The system was designed as a prototype for a field deployable system. Therefore, custom electronics were designed and other efforts were made such that the entire system could fit on a small lab cart and be moved by a single person. Possible applications include search and monitoring of radionuclide material. Various images are shown and the ability of the imager to find a source in the presence of high background is demonstrated. The absolute imaging efficiency or the detector at 511 keV is shown to be /spl sim/ 4 * 10/sup -3/ for this system. Of events that deposited their full energy in the detector, it is shown that /spl sim/20% are suitable for imaging using current techniques. Methods to improve the efficiency in future systems are discussed.

A germanium gamma ray imager with 3D position sensitivity

A germanium based gamma ray imager with 3D position sensitivity is being developed. The imager will detect gamma rays in the range of /spl sim/10 keV to 1.5 MeV and locate their interactions in the germanium to within 2 mm in X, Y and Z. The instrument is segmented into 39 orthogonal strips in both the X and Y directions with a 2 mm pitch. Each channel is separately instrumented with a miniature low-noise charge-sensitive preamplifier followed by shaping and timing electronics. Germanium based imagers with 2-D position sensitivity have recently been developed and fully instrumented by our group. The current instrument adds the capability for determining the Z position (depth of interaction). The Z coordinate is found by looking at the relative timing of the signals induced by the drifting electrons and holes. A relatively simple analog approach for determining the depth of interaction was implemented. Some of the intended applications for this type of instrument include balloon based imaging experiments and field portable devices for environmental remediation. Therefore, much of the effort was concentrated on developing a detector and electronics scheme that was simple, compact, and low power. The instrument is described with emphasis on the technique used for measuring the Z coordinate. Results obtained from spectroscopy as well as Z position measurements are shown.