Large-Format, High-Throughput Photon-Counting Imager

Low-cost, power-efficient, time-resolved imaging is increasingly important for DOE remote sensing operations. While large-area CMOS and CCD visible imagers and high-resolution thermal imagers now provide excellent images, these technologies do not have the temporal resolution to detect and track transient events, such as lasers, muzzle flashes, or other energetic events. Needed are imagers that have the sensitivity and time response of photomultiplier tubes, with the spatial resolution of video imagers, and which are compatible with the size, weight, and power constraints of unmanned aircraft and small space platforms. General statement of how this problem is being addressed: To improve upon the performance of contemporary microchannel plate image tube and video imager technology, a solid-state single-photon avalanche detector (SPAD) array capable of the sensitivity, resolution, and count rates required of remote sensing and surveillance applications is being developed. A monolithic asynchronous time-resolved solid-state silicon imager with 1024 x 1024-element resolution is being developed. Each ~15-micron pixel includes a low-dark-count, high efficiency, single-photon avalanche diode (SPAD) element, with active quenching and enable logic. As photons arrive, they are time-stamped to sub-100-ps resolution. The single-photon sensitivity and asynchronous readout allow the imager to detect photon flux rates, ranging from one photon per minute to one billion photons per second. The high dynamic range and fine time resolution also make the SPAD array ideal for low-light-level night imaging and 3D LADAR imaging. What is to be done in Phase I: In Phase, after testing and characterizing existing circuits and devices, including the single-photon-sensitive detector elements, active quenching circuits (AQC), pixel-readout circuits, event-driven readout address-arbitration logic, and time-to-digital converter (TDC) circuits, the performance of the components will be optimized, and a fully functional, 1024 x 1024-element array will be designed and its performance simulated. A small-sized test array will be layed out, verified, and taped out for fabrication, so that it is available for characterization early in Phase II, reducing risk. Commercial Applications and Other Benefits: The ability of the innovation to achieve both high spatial and temporal resolution, at the lowest possible data bandwidths, makes it an enabling technology for a number of important scientific, medical, industrial, and consumer applications, including low-light-level imaging, laser detection and ranging (LADAR), automobile collision avoidance and navigation, nuclear imaging, etc. Included in the scientific applications are combined laser Raman spectroscopy, time-resolved fluorescence spectroscopy/imaging, and laser-induced breakdown spectroscopy (LIBS). Key Words: Single photon counting, hybrid image tube, low light level imaging, micro-channel plate, MCP, hybrid image tube, time to digital converter, CMOS imager automotive imaging capabilities and engender new science experiments.