David M. Craig

Progress on color night vision: visible/IR fusion, perception and search, and low-light CCD imaging

We report progress on our development of a color night vision capability, using biological models of opponent-color processing to fuse low-light visible and thermal IR imagery, and render it in realtime in natural colors. Preliminary results of human perceptual testing are described for a visual search task, the detection of embedded small low-contrast targets in natural night scenes. The advantages of color fusion over two alterative grayscale fusion products is demonstrated in the form of consistent, rapid detection across a variety of low- contrast (+/- 15% or less) visible and IR conditions. We also describe advances in our development of a low-light CCD camera, capable of imaging in the visible through near- infrared in starlight at 30 frames/sec with wide intrascene dynamic range, and the locally adaptive dynamic range compression of this imagery. Example CCD imagery is shown under controlled illumination conditions, from full moon down to overcast starlight. By combining the low-light CCD visible imager with a microbolometer array LWIR imager, a portable image processor, and a color LCD on a chip, we can realize a compact design for a color fusion night vision scope.

A Study of Crosstalk in a

We demonstrate a 256 × 256 passive photon counting imager based on hybridization of back-illuminated silicon Geiger-mode avalanche photodiodes to an all-digital CMOS counting chip. Photon detection efficiencies in the 10%-20% are observed at visible wavelengths. The detection efficiency is currently limited by optical crosstalk that leads to elevation of dark count rates as the bias voltage on the photodiodes is increased. Both the time dependence of dark count activity during a gate time and the spatial structure of dark images were successfully explained using crosstalk-based models.

256 \times 256

We report an array of Shack-Hartmann wavefront sensors using high-fill-factor Geiger-mode avalanche detector quad cells hybridized to all-digital CMOS counting circuits. The absence of readout noise facilitates fast wavefront sensing at low light levels.

Photon Counting Imager Based on Silicon Geiger-Mode Avalanche Photodiodes

A stepper operating at the 193-nm wavelength has been constructed for use in the development of resist processes. The stepper lens has a 4-mm field diameter and a 0.33 NA. The stepper uses an unnarrowed ArF excimer laser as the light source, and uses diffractive lenslet arrays to transform the low divergence excimer beam into a suitable pupil fill. The stepper is routinely used for resist studies and has been used to pattern lines and spaces as small as 0.15 ?m.

Geiger-mode quad-cell array for adaptive optics

The orthogonal-transfer array (OTA) is a new CCD architecture designed to provide wide-field tip-tilt correction of astronomical images. The device consists of an 8x8 array of small (~500x500 pixels) orthogonal-transfer CCDs (OTCCD) with independent addressing and readout of each OTCCD. This approach enables an optimum tip-tilt correction to be applied independently to each OTCCD across the focal plane. The first design of this device has been carried out at MIT Lincoln Laboratory in support of the Pan-STARRS program with a collaborative parallel effort at Semiconductor Technology Associates (STA) for the WIYN Observatory. The two versions of this device are functionally compatible and share a common pinout and package. The first wafer lots are complete at Lincoln and at Dalsa and are undergoing wafer probing.

Small-field stepper for 193-nm lithography process development

Future X-ray missions such as Lynx require large-format imaging detectors with performance at least as good as the best current-generation devices but with much higher readout rates. We are investigating a Digital CCD detector architecture, under development at MIT Lincoln Laboratory, for use in such missions. This architecture features a CMOS-compatible detector integrated with parallel CMOS signal processing chains. Fast, low-noise amplifiers and highly parallel signal processing provide the high frame-rates required. CMOS-compatibility of the CCD provides low-power charge transfer and signal processing. We report on the performance of CMOS-compatible test CCDs read at rates up to 5 Mpix s−1 (50 times faster than Chandra ACIS CCDs), with transfer clock swings as low as ±1.5 V (power/area < 10% of that of ACIS CCDs). We measure read noise below 6 electrons RMS at 2.5 MHz and X-ray spectral resolution better than 150 eV FWHM at 5.9 keV for single-pixel events. We discuss expected detector radiation tolerance at these relatively high transfer rates. We point out that the high pixel ’aspect ratio’ (depletion-depth : pixel size ≈ 9 : 1) of our test devices is similar to that expected for Lynx detectors, and illustrate some of the implications of this geometry for X-ray performance and noise requirements.

The orthogonal-transfer array: a new CCD architecture for astronomy

The detection statistics of Geiger-mode photodetector subarrays with a combination of reset-time blocking loss and optical crosstalk are investigated. Closed-form expressions are obtained for the means and covariances of the numbers of counts in 2 × 2 subarrays (quad cells) used in Shack-Hartmann wavefront sensors. The predicted wavefront sensing precision is compared with that obtained with a charge-coupled device-based wavefront sensor with readout noise. The results of the theory are also used to predict photon transfer curves for the Geiger-mode device and these are compared with experiment.

Toward fast, low-noise, low-power digital CCDs for Lynx and other high-energy astrophysics missions

A 512/spl times/512-element, multi-frame charge-coupled device (CCD) has been developed for collecting four sequential image frames at megahertz rates. To operate at fast frame rates with high sensitivity, the imager uses an electronic shutter technology developed for back-illuminated CCDs. The megahertz frame rates also required metal strapping of the polysilicon gate electrodes. Tested imagers have demonstrated multi-frame capture capability.

Detection Statistics in Geiger-Mode Avalanche Photodiode Quad-Cell Arrays With Crosstalk and Dead Time

Gigahertz (GHz) imaging technology will be needed at high-luminosity X-ray and charged particle sources. It is plausible to combine fast scintillators with the latest picosecond detectors and GHz electronics for multi-frame hard Xray imaging and achieve an inter-frame time of less than 10 ns. The time responses and light yield of LYSO, LaBr3, BaF2 and ZnO are measured using an MCP-PMT detector. Zinc Oxide (ZnO) is an attractive material for fast hard X-ray imaging based on GEANT4 simulations and previous studies, but the measured light yield from the samples is much lower than expected.

High-fill-factor, burst-frame-rate charge-coupled device

A 512/spl times/512-element, multi-frame charge-coupled device (CCD) has been developed for collecting four sequential image frames at megahertz rates. To operate at fast frame rates with high sensitivity, the imager uses an electronic shutter technology developed for back-illuminated CCDs. The megahertz frame rates also required metal strapping of the polysilicon gate electrodes. Tested imagers have demonstrated multi-frame capture capability.