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The general architecture of the imaging array, some merits of HgCdTe-on-sapphire as a detector material, and the current status of the laboratory tests and the Short Wave Infrared (SWIR) camera are described.
An instrument that functions mainly as a particle-image velocimeter provides data on the sizes and velocities of flying opaque particles. The instrument is being developed as a means of characterizing fluxes of wind-borne dust particles in the Martian atmosphere. The instrument could also adapted to terrestrial use in measuring sizes and velocities of opaque particles carried by natural winds and industrial gases. Examples of potential terrestrial applications include monitoring of airborne industrial pollutants and airborne particles in mine shafts. The design of this instrument reflects an observation, made in field research, that airborne dust particles derived from soil and rock are opaque enough to be observable by use of bright field illumination with high contrast for highly accurate measurements of sizes and shapes. The instrument includes a source of collimated light coupled to an afocal beam expander and an imaging array of photodetectors. When dust particles travel through the collimated beam, they cast shadows. The shadows are magnified by the beam expander and relayed to the array of photodetectors. Inasmuch as the images captured by the array are of dust-particle shadows rather of the particles themselves, the depth of field of the instrument can be large: the instrument has a depth of field of about 11 mm, which is larger than the depths of field of prior particle-image velocimeters. The instrument can resolve, and measure the sizes and velocities of, particles having sizes in the approximate range of 1 to 300 m. For slowly moving particles, data from two image frames are used to calculate velocities. For rapidly moving particles, image smear lengths from a single frame are used in conjunction with particle- size measurement data to determine velocities.
A digital mammography device uses a mosaic of electronic digital imaging arrays to scan an x-ray image is discussed. The mosaic of arrays is repositioned several times to expose different portions of the image, until the entire image is scanned. The data generated by the arrays during each exposure is stored in a computer. After the final exposure, the computer combines data of the several partial images to produce a composite of the original x-ray image. An aperture plate is used to reduce scatter and the overall exposure of the patient to x-rays.
Array camera images of the central 1 parsec of the Galactic Center at eight mid-infrared wavelengths between 4.8 and 20.0 microns with approximately 1 arcsec resolution are used to model the temperature, opacity and bolometric luminosity distributions of the emitting dust in the central parsec, and the extinction in the line of sight. We use the results to discriminate between two mechanisms for heating the dust: heating by radiation from a "central engine" (possibly a massive black hole associated with Sgr A*), or internal heating by luminous stars embedded in or among the dust clouds. The temperature and opacity distributions are consistent with the presence of self-luminous objects imbedded at prominent the IRS source positions. However, temperatures on the northern ann and east-west bar are highest along the inner flank of those structures surrounding the central cavity, while the dust opacity peaks further out from the central cavity. The warm inner ridge suggests heating by centrally located concentrated luminous sources, including IRS3 and IRS7. The of the model results are compared with the distributions of the various stellar populations in the central parsec. There is evidence for physical interaction between the warm emitting dust and luminous stars, including dozens of hot He1 emission line stars and B[] stars. The combined contributions of embedded stars at the IRS source positions and the luminous stars distributed throughout Sgr A West can account for the temperature enhancements and the luminosity distribution in the central parsec computed by the model.
Discussion of approaches to providing the needed performance improvement in solid state sensor systems for remote sensing from future resources surveying satellites. An advanced breadboard line array imaging system using long detector arrays from a number of small chips has been built. Test results and typical imagery produced by the breadboard system demonstrate the capabilities of solid state imager technology.
Sensors Unlimited, Inc., with SBIR funding from NASA's Langley Research Center, Goddard Space Flight Center, Marshall Space Flight Center, and the Jet Propulsion Laboratory, developed a monolithic focal plane array for near-infrared imaging. The company developed one- (1- D) and two-dimensional (2-D) imaging arrays consisting of a highly reliable InGaAs p-I-n diode as a photodetector for monitoring a variety of applications, including single element device applications in receivers. The InGaAs 1-D and 2-D arrays have many applications. For example, they monitor the performance of dense wavelength division multiplexing (DWDM) systems- the process of packaging many channels into a single fiber-optic cable. Sensors Unlimited commercially offers its LXTM and LYTM Series InGaAs linear arrays for reliable DWDM performance monitoring. The LX and LY arrays enable instrument module designs with no moving parts, which provides for superior uniformity, and fast, linear outputs that remain stable over a wide temperature range. Innovative technologies derived from the monolithic focal plane array have enabled telecommunication companies to optimize existing bandwidth in their fiber-optic networks in order to support a high volume of network traffic. At the same time, the technologies obtained from the array have the potential for reducing costs, while increasing performance from Sensors Unlimited's current product lines.
The Chandra X-ray Observatory (CXO) observed Jupiter during the period 2003 February 24-26 for approx.40 hours (4 Jupiter rotations), using both the spectroscopy array of the Advanced CCD Imaging Spectrometer (ACIS-S) and the imaging array of the High-Resolution Camera (HRC-I). Two ACIS-S exposures, each approx.8.5 hr long, were separated by an HRC-I exposure of approx.20 hr. The low- to mid-latitude non-auroral disk X-ray emission is much more spatially uniform than the auroral emission. However, the low- to mid-latitude X-ray count rate shows a small but statistically significant hour angle dependence, and is higher in regions of relatively low surface magnetic field strength, confirming ROSAT results. In addition, the spectrum from the low surface field region shows an enhancement in the energy band 1.14- 1.38 keV, perhaps partly due to line emission from that region. Correlation of surface magnetic field strength with count rate is not found for the 2000 December HRC-I data, at a time when solar activity was high. The low- to mid-latitude disk X-ray count rate observed by the HRC-I in the 2003 February observation is about 50% of that observed in 2000 December, roughly consistent with a decrease in the solar activity index (F10.7 cm flux) by a similar amount over the same time period. The low- to mid-latitude X-ray emission does not show any oscillations similar to the -45 minute oscillations sometimes seen from the northern auroral zone. The temporal variation in Jupiter's non-auroral X-ray emission exhibits similarities to variations in solar X-ray flux observed by GOES and TIMED/SEE. The two ACIS-S 0.3-2 keV low- to mid-latitude X-ray spectra are harder than the auroral spectrum, and are different from each other at energies above 0.7 keV, showing variability in Jupiter s non-auroral X-ray emission on a time scale of a day. The 0.3-2.0 keV X-ray power emitted at low- to mid-latitudes is 0.21 GW and 0.39 GW for the first and second ACIS-S exposures, respectively. We suggest that X-ray emission from Jupiter's disk may be largely generated by solar X-rays resonantly and fluorescently scattered in its upper atmosphere, especially at times of high incident solar X-ray flux. However, the correlation of higher count rate with low surface magnetic-field strength indicates the presence of some secondary component, possibly ion precipitation from radiation belts closer to the planet than elsewhere at low- to mid-latitudes.
The Chandra X-ray Observatory (CXO) observed Jupiter during the period 24-26 February 2003 for approx. 40 hours (4 Jupiter rotations), using both the spectroscopy array of the Advanced CCD Imaging Spectrometer (ACIS-S) and the imaging array of the High-Resolution Camera (HRC-I). Two ACIS-S exposures, each -8.5 hours long, were separated by an HRC-I exposure of approx. 20 hours. The low- to middle-latitude nonauroral disk X-ray emission is much more spatially uniform than the auroral emission. However, the low- to middle-latitude X-ray count rate shows a small but statistically significant hour angle dependence and depends on surface magnetic field strength. In addition, the X-ray spectra from regions corresponding to 3-5 gauss and 5-7 gauss surface fields show significant differences in the energy band 1.26-1.38 keV, perhaps partly due to line emission occurring in the 3-5 gauss region but not the 5-7 gauss region. A similar correlation of surface magnetic field strength with count rate is found for the 18 December 2000 HRC-I data, at a time when solar activity was high. The low- to middle-latitude disk X-ray count rate observed by the HRC-I in the February 2003 observation is about 50% of that observed in December 2000, roughly consistent with a decrease in the solar activity index (F10.7 cm flux) by a similar amount over the same time period. The low- to middle-latitude X-ray emission does not show any oscillations similar to the approx. 45 min oscillations sometimes seen from the northern auroral zone. The temporal variation in Jupiter's nonauroral X-ray emission exhibits similarities to variations in solar X-ray flux observed by GOES and TIMED/SEE. The two ACIS-S 0.3-2.0 keV low- to middle-latitude X-ray spectra are harder than the auroral spectrum and are different from each other at energies above 0.7 keV, showing variability in Jupiter's nonauroral X-ray emission on a timescale of a day. The 0.3-2.0 keV X-ray power emitted at low to middle latitudes is 0.21 GW and 0.39 GW for the first and second ACIS-S exposures, respectively. We suggest that X-ray emission from Jupiter's disk may be largely generated by the scattering and fluorescence of solar X rays in its upper atmosphere, especially at times of high incident solar X-ray flux. However, the dependence of count rate on surface magnetic-field strength may indicate the presence of some secondary component, possibly ion precipitation from radiation belts close to the planet.
There has been much interest in very long-wavelength quantum well infrared photodetectors and associated intersubband absorption due to their mature technology and the possibility of producing high performance large area two-dimensional imaging arrays.
Design, simulation, fabrication, and measurement have been performed using a new method for obtaining high-speed p-i-n germanium photodiodes for use in backside imaging arrays. These devices are proof-of-principal in situ-doped vertical mesa structures fabricated using single-wafer, atmospheric-pressure chemical vapor deposition (APCVD) homoepitaxy on Czochralski-grown Ge substrates. Excellent impurity profiles resulting from in situ doping, as measured by spreading-resistance profilometry, were 5 × 10 16 , 2 × 10 15 , and 2 × 10 18 (cm -3 ) for the p-type anode, i-region absorber, and n+ cathode, respectively. Scanning electron microscopy analysis revealed very-low defect densities in the epitaxial layers. The diodes, with diameters ranging 100-500 μm, exhibited excellent ideality (n = 1.15) and less than 1-μA dark current, corresponding to up to 80 kV-cm -1 electric field in the smallest devices. Avalanche breakdown bias was consistently at a magnitude of 50 V or lower. External quantum efficiencies in the near-infrared spectrum peaked at 70%. Pulsed illumination experiments, both in the infrared and X-ray regions, showed pulse rise times in the 100-140 ps range, indicating excellent applicability of this method to high-speed X-ray or infrared applications.
Nano-multiplication-region avalanche photodiodes (NAPDs), and imaging arrays of NAPDs integrated with complementary metal oxide/semiconductor (CMOS) active-pixel-sensor integrated circuitry, are being developed for applications in which there are requirements for high-sensitivity (including photoncounting) detection and imaging at wavelengths from about 250 to 950 nm. With respect to sensitivity and to such other characteristics as speed, geometric array format, radiation hardness, power demand of associated circuitry, size, weight, and robustness, NAPDs and arrays thereof are expected to be superior to prior photodetectors and arrays including CMOS active-pixel sensors (APSs), charge-coupled devices (CCDs), traditional APDs, and microchannelplate/ CCD combinations. Figure 1 depicts a conceptual NAPD array, integrated with APS circuitry, fabricated on a thick silicon-on-insulator wafer (SOI). Figure 2 presents selected aspects of the structure of a typical single pixel, which would include a metal oxide/semiconductor field-effect transistor (MOSFET) integrated with the NAPD. The NAPDs would reside in silicon islands formed on the buried oxide (BOX) layer of the SOI wafer. The silicon islands would be surrounded by oxide-filled insulation trenches, which, together with the BOX layer, would constitute an oxide embedding structure. There would be two kinds of silicon islands: NAPD islands for the NAPDs and MOSFET islands for in-pixel and global CMOS circuits. Typically, the silicon islands would be made between 5 and 10 m thick, but, if necessary, the thickness could be chosen outside this range. The side walls of the silicon islands would be heavily doped with electron-acceptor impurities (p+-doped) to form anodes for the photodiodes and guard layers for the MOSFETs. A nanoscale reach-through structure at the front (top in the figures) central position of each NAPD island would contain the APD multiplication region. Typically, the reach-through structure would be about 0.1 microns in diameter and between 0.3 and 0.4 nm high. The top layer in the reach-through structure would be heavily doped with electron-donor impurities (n+-doped) to make it act as a cathode. A layer beneath the cathode, between 0.1 and 0.2 nm thick, would be p-doped to a concentration .10(exp 17)cu cm. A thin n+-doped polysilicon pad would be formed on the top of the cathode to protect the cathode against erosion during a metal-silicon alloying step that would be part of the process of fabricating the array.
Soft X-ray imaging is a powerful tool to explore the structure of cells, probe material with nanometer resolution, and investigate the energetic phenomena in the universe. Conventional soft X-ray image sensors are by and large Si-based charge coupled devices that suffer from low frame rates, complex fabrication processes, mechanical inflexibility, and required cooling below -60 °C. Here, a soft X-ray photodiode is reported based on low-cost metal halide perovskite with comparable performance to commercial Si-based device. Nanothrough network electrode minimized the optical loss due to the shadowing of insensitive layers, while a multidimensional perovskite heterojunction is generated to reduce the photo-generated carrier loss. Further, this strategy promoted a record quantum efficiency of 8 × 10 3 % without cooling, several orders of magnitude greater than the previously achieved. Flexible and curved soft X-ray imaging arrays are fabricated based on this high-performance device structure, demonstrating stable soft X-ray response and sharp imaging capabilities. This work highlights the low-cost and efficient perovskite photodiode as a strong candidate for the next-generation soft X-ray image sensors.
A star sensor for measuring small pointing errors in astronomical telescopes is described. By using solid state imaging arrays (CCDs) to track guide star images, this design realizes a number of performance advantages relative to more conventional approaches. Specific topics include star image position measurement, CCD sensitivity including color effects, and performance simulation results. Experimental results for CCDs operating at temperatures below 100 K are also summarized. Two telescope configurations are considered to illustrate the range of possible applications of this technology: (1) a large orbiting telescope for general astronomy requiring a multi-CCD sensor, and (2) a Space Shuttle-based infrared observatory operating at 20 K. Although the requirements and configurations of these applications are widely different, the CCD approach offers substantial advantages to both systems.
Future instruments for the 100-10,000 A UV-wavelength region will require detectors with greater quantum efficiency, smaller picture elements, a greater wavelength range, and greater active area than those currently available. After assessing the development status and performance characteristics of vidicons, image tubes, electronographic cameras, digicons, silicon arrays and microchannel plate intensifiers presently employed by astronomical spacecraft, attention is given to such next-generation detectors as the Mosaicked Optical Self-scanned Array Imaging Camera, which consists of a photocathode deposited on the input side of a microchannel plate intensifier. The problems posed by the signal processing and data analysis requirements of the devices foreseen for the 21st century are noted.
The present invention relates generally to a mammography device and method and more particularly to a novel digital mammography device and method to detect microcalcifications of precancerous tissue. A digital mammography device uses a mosaic of electronic digital imaging arrays to scan an x-ray image. The mosaic of arrays is repositioned several times to expose different portions of the image, until the entire image is scanned. The data generated by the arrays during each exposure is stored in a computer. After the final exposure, the computer combines data of the several partial images to produce a composite of the original x-ray image. An aperture plate is used to reduce scatter and the overall exposure of the patient to x-rays. The novelty of this invention is that it provides a digital mammography device with large field coverage, high spatial resolution, scatter rejection, excellent contrast characteristics and lesion detectability under clinical conditions. This device also shields the patient from excessive radiation, can detect extremely small calcifications and allows manipulation and storage of the image.
A programmable CCD (charge-coupled device) driver circuit was designed to drive CCDs in multiphased modes. The purpose of the drive electronics is to operate developmental CCD imaging arrays for NASA's tiltable moderate resolution imaging spectrometer (MODIS-T). Five objectives for the driver were considered during its design: (1) the circuit drives CCD electrode voltages between 0 V and +30 V to produce reasonable potential wells, (2) the driving sequence is started with one input signal, (3) the driving sequence is started with one input signal, (4) the circuit allows programming of frame sequences required by arrays of any size, (5) it produces interfacing signals for the CCD and the DTF (detector test facility). Simulation of the driver verified its function with the master clock running up to 10 MHz. This suggests a maximum rate of 400,000 pixels/s. Timing and packaging parameters were verified. The design uses 54 TTL (transistor-transistor logic) chips. Two versions of hardware were fabricated: wirewrap and printed circuit board. Both were verified functionally with a logic analyzer.
In this paper, we discuss the development of very sensitive long wavelength infrared (LWIR) GaAs/AlGal-xAs Quantum well infrared photodetectors (QWIPS), fabrication of random reflectors for efficient light coupling, and the demonstration of a LWIR 256 X 256 focal plane array imaging camera. Excellent imagery, with a noise equivalent differential temperature (NE-delta-T) of 25 mK has been achieved.
Array images of Orion BN/KL at nine midinfrared (5-20 microns) wavelengths have revealed a subarcsecond structure near IRc2 which provides new constraints on the relationship between IRc2 and the Orion SiO maser. The infrared source positions have been improved, and IRc2 is found to be displaced 0.8 +/- 0.2 arcsec (at least 400 AU) from the SiO maser, an order of magnitude greater than the separation assumed in the current maser model. The SiO maser and the IRc2 midinfrared source may be physically independent objects. There are indications that IRc2 is eroded on the south side adjacent to the SiO/H2O maser cluster, suggesting that another luminous object near IRc2, most likely a stellar object associated with radio continuum point source 'I', is the host for the Orion SiO maser.