The performance of short-wavelength infrared (SWIR) cameras in the visible and ultraviolet (UV) regions is limited by the absorption of high-energy photons in inactive regions of the imaging array. Dual-band UV-SWIR imaging can be achieved by using PbS colloidal quantum dots (CQD) to downshift incident UV light to the SWIR band. The CQD downshifting layer has minimal impact on the SWIR imaging performance and greatly increases the UV sensitivity of an InGaAs camera. A dual-lens design in which the QDs are incorporated on a removable substrate is demonstrated, which provides UV sensitivity without modification of the InGaAs camera focal plane array. A single-lens design in which the QDs are deposited directly on the focal plane array is demonstrated using both a standard InGaAs focal plane and a substrate-thinned focal plane. Higher UV resolution for the substrate-thinned focal plane is observed.
The unique linear avalanche properties of HgCdTe preserve the Poisson statistics of the incoming photons, opening up
new opportunities for GHz bandwidth LADAR and space communications applications. Raytheon has developed and
previously reported (1) unique linear mode photon counting arrays based on combining advanced HgCdTe linear mode
APDs with their high gain SB415B readout. Their use of HgCdTe APDs preserves the Poisson statistics of the incoming
photons, enabling (noiseless) photon counting. This technology is of great potential interest to infrared astronomy but
requires extension of noiseless linear HgCdTe avalanching down to much lower bandwidths (100 to 0.001 Hz) with
corresponding reductions in dark count rate.
We have hybridized the SB415B readout to SWIR HgCdTe APDs optimized for low dark count rate and have
characterized their photon counting properties at bandwidths down to 1 KHz. As bandwidth is reduced, the performance
becomes limited by the intrinsic properties of the SB415B readout, particularly readout glow, stability and 1/f noise.
We report the results of these measurements and the status of hybrid arrays utilizing a newly developed readout which
draws on Raytheon’s astronomical readout heritage, specifically the Virgo charge integrating source follower, as a path
to much lower dark count rate photon counting operation.
Raytheon is developing NIR sensor chip assemblies (SCAs) for scanning and staring 3D LADAR systems. High
sensitivity is obtained by integrating high performance detectors with gain, i.e., APDs with very low noise Readout
Integrated Circuits (ROICs). Unique aspects of these designs include: independent acquisition (non-gated) of pulse
returns, multiple pulse returns with both time and intensity reported to enable full 3D reconstruction of the image.
Recent breakthrough in device design has resulted in HgCdTe APDs operating at 300K with essentially no excess noise
to gains in excess of 100, low NEP <1nW and GHz bandwidths and have demonstrated linear mode photon counting.
SCAs utilizing these high performance APDs have been integrated and demonstrated excellent spatial and range
resolution enabling detailed 3D imagery both at short range and long ranges. In the following we will review progress in
real-time 3D LADAR imaging receiver products in three areas: (1) scanning 256 × 4 configuration for the Multi-Mode
Sensor Seeker (MMSS) program and (2) staring 256 × 256 configuration for the Autonomous Landing and Hazard
Avoidance Technology (ALHAT) lunar landing mission and (3) Photon-Counting SCAs which have demonstrated a
dramatic reduction in dark count rate due to improved design, operation and processing.
Linear mode photon counting (LMPC) provides significant advantages in comparison with Geiger Mode (GM) Photon
Counting including absence of after-pulsing, nanosecond pulse to pulse temporal resolution and robust operation in the
present of high density obscurants or variable reflectivity objects. For this reason Raytheon has developed and
previously reported on unique linear mode photon counting components and modules based on combining advanced
APDs and advanced high gain circuits. By using HgCdTe APDs we enable Poisson number preserving photon counting.
A metric of photon counting technology is dark count rate and detection probability. In this paper we report on a
performance breakthrough resulting from improvement in design, process and readout operation enabling >10x
reduction in dark counts rate to ~10,000 cps and >104x reduction in surface dark current enabling long 10 ms
integration times. Our analysis of key dark current contributors suggest that substantial further reduction in DCR to
~ 1/sec or less can be achieved by optimizing wavelength, operating voltage and temperature.
Raytheon is developing NIR sensor chip assemblies (SCAs) for scanning and staring 3D LADAR systems. High
sensitivity is obtained by integrating high performance detectors with gain, i.e., APDs with very low noise Readout
Integrated Circuits (ROICs). Unique aspects of these designs include: independent acquisition (non-gated) of pulse
returns, multiple pulse returns with both time and intensity reported to enable full 3D reconstruction of the image.
Recent breakthrough in device design has resulted in HgCdTe APDs operating at 300K with essentially no excess noise
to gains in excess of 100, low NEP <1nW and GHz bandwidths and have demonstrated linear mode photon counting.
SCAs utilizing these high performance APDs have been integrated and demonstrated excellent spatial and range
resolution enabling detailed 3D imagery both at short range and long ranges. In the following we will review progress in
real-time 3D LADAR imaging receiver products in two areas: (1) scanning 256 × 4 configuration for the Multi-Mode
Sensor Seeker (MMSS) program and (2) staring 256 × 256 configuration for the Autonomous Landing and Hazard
Avoidance Technology (ALHAT) lunar landing mission.
Raytheon is developing NIR sensor chip assemblies (SCAs) for scanning and staring 3D LADAR systems. High
sensitivity is obtained by integrating high performance detectors with gain i.e. APDs with very low noise Readout
Integrated Circuits. Unique aspects of these designs include: independent acquisition (non-gated) of pulse returns,
multiple pulse returns with both time and intensity reported to enable full 3D reconstruction of the image. Recent
breakthrough in device design has resulted in HgCdTe APDs operating at 300K with essentially no excess noise to gains
in excess of 100, low NEP <1nW and GHz bandwidths and have demonstrated linear mode photon counting. SCAs
utilizing these high performance APDs have been integrated and demonstrated excellent spatial and range resolution
enabling detailed 3D imagery both at short range and long ranges. In this presentation we will review progress in high
resolution scanning, staring and ultra-high sensitivity photon counting LADAR sensors.
Raytheon Vision Systems (RVS) has obtained the initial performance data on a
1280x1024 format short wave infrared (SWIR) sensor with a dark current of 1
nA/cm2 and low noise input circuit of five noise electrons (5 e-), which is 2× lower
electronic read-out noise and 2× lower dark current than previous designs. A
remarkable feature of the sensor is that a novel high dynamic range circuit is also
designed into the 15 × 15 μm pixel unit cell, in a large format, high density
1280×1024 SWIR FPA. The integration of the conflicting design requirements of
extremely low noise with high dynamic range allows recognition of low contrast
targets, without saturation from bright sources within the same frame of information.
This enables operation in urban environments at low levels of ambient illumination,
and simultaneously with bright sources that saturate conventional sensors.
J. Asbrock, S. Bailey, D. Baley, J. Boisvert, G. Chapman, G. Crawford, T. de Lyon, B. Drafahl, J. Edwards, E. Herrin, C. Hoyt, M. Jack, R. Kvaas, K. Liu, W. McKeag, R. Rajavel, V. Randall, S. Rengarajan, J. Riker
Advanced LADAR receivers enable high accuracy identification of targets at ranges beyond standard EOIR sensors. Increased sensitivity of these receivers will enable reductions in laser power, hence more affordable, smaller sensors as well as much longer range of detection. Raytheon has made a recent breakthrough in LADAR architecture by combining very low noise ~ 30 electron front end amplifiers with moderate gain >60 Avalanche Photodiodes. The combination of these enables detection of laser pulse returns containing as few as one photon up to 1000s of photons. Because a lower APD gain is utilized the sensor operation differs dramatically from traditional "Geiger mode APD" LADARs. Linear mode photon counting LADAR offers advantages including: determination of intensity as well as time of arrival, nanosecond recovery times and discrimination between radiation events and signals. In our talk we will present an update of this development work: the basic amplifier and APD component performance, the front end architecture, the demonstration of single photon detection using a simple 4 × 4 SCA and the design and evaluation of critical components of a fully integrated photon counting camera under development in support of the Ultra-Sensitive Detector (USD) program sponsored by AFRL-Kirtland.
Michael Jack, Jim Asbrock, Steven Bailey, Diane Baley, George Chapman, Gina Crawford, Betsy Drafahl, Eileen Herrin, Robert Kvaas, William McKeag, Valerie Randall, Terry De Lyon, Andy Hunter, John Jensen, Tom Roberts, Patrick Trotta, T. Dean Cook
Raytheon is developing HgCdTe APD arrays and sensor chip assemblies (SCAs) for scanning and staring LADAR systems. The nonlinear characteristics of APDs operating in moderate gain mode place severe requirements on layer thickness and doping uniformity as well as defect density. MBE based HgCdTe APD arrays, engineered for high performance, meet the stringent requirements of low defects, excellent uniformity and reproducibility. In situ controls for alloy composition and substrate temperature have been implemented at HRL, LLC and Raytheon Vision Systems and enable consistent run to run results. The novel epitaxial designed using separate absorption-multiplication (SAM) architectures enables the realization of the unique advantages of HgCdTe including: tunable wavelength, low-noise, high-fill factor, low-crosstalk, and ambient operation. Focal planes built by integrating MBE detectors arrays processed in a 2 x 128 format have been integrated with 2 x 128 scanning ROIC designed. The ROIC reports both range and intensity and can detect multiple laser returns with each pixel autonomously reporting the return. FPAs show exceptionally good bias uniformity <1% at an average gain of 10. Recent breakthrough in device design has resulted in APDs operating at 300K with essentially no excess noise to gains in excess of 100, low NEP <1nW and GHz bandwidth. 3D LADAR sensors utilizing these FPAs have been integrated and demonstrated both at Raytheon Missile Systems and Naval Air Warfare Center Weapons Division at China Lake. Excellent spatial and range resolution has been achieved with 3D imagery demonstrated both at short range and long range. Ongoing development under an Air Force Sponsored MANTECH program of high performance HgCdTe MBE APDs grown on large silicon wafers promise significant FPA cost reduction both by increasing the number of arrays on a given wafer and enabling automated processing.
Transmittance spectra of solid and vapor samples of trinitrotoluene (TNT) in the spectral range 0.6 to 10 THz at
resolutions up to 1 GHz are reported. Uniform solid samples of ~100 &mgr;m thickness gave stronger absorption and more
resolved structure than previous studies. New absorption lines for TNT solid below 100 cm-1 are reported. A heated 10
m multpass White cell was used for spectroscopy of the vapor. Strong absorption bands yield unexpectedly large
absorption cross sections for the anticipated saturated vapor pressure at the cell temperature, leaving their assignment to
TNT in doubt. These results indicate that path lengths exceeding 10 m and temperatures higher than 40 C, or
significantly higher instrumental sensitivity, are needed for sensing of TNT vapor in the spectral range 0.6 to 10 THz.
Millimeter-wave (mmw) imagers offer advantages for numerous applications, including: all weather reconnaissance, search and rescue, law enforcement, and security screening for homeland defense. The use of bolometer-based imagers for mmw provides potential advantages of low power, small size, weight, and cost. In addition, bolometer-based imagers provide the unique capability of detection over an enormous spectral range, i.e., from mmw through the sub-mmw (from 100 GHz through greater than 1 THz). We report on high-resolution materials transmission measurements as well as advances in mmw imager architectures that seek to exploit improved imager sensitivity and resolution enabled by operation at sub-mmw and THz frequencies
Since its initial synthesis and investigation more than 40 years ago, the HgCdTe alloy semiconductor system has evolved into one of the primary infrared detector materials for high-performance infrared focal-plane arrays (FPA) designed to operate in the 3-5 mm and 8-12 mm spectral ranges of importance for thermal imaging systems. Over the course of the past decade, significant advances have been made in the development of thin-film epitaxial growth techniques, such as molecular-beam epitaxy (MBE), which have enabled the synthesis of IR detector device structures with complex doping and composition profiles. The central role played by in situ sensors for monitoring and control of the MBE growth process are reviewed. The development of MBE HgCdTe growth technology is discussed in three particular device applications: avalanche photodiodes for 1.55 +m photodetection, megapixel FPAs on Si substrates, and multispectral IR detectors.
Michael Jack, James Asbrock, C. Anderson, Steven Bailey, George Chapman, E. Gordon, P. Herning, Murray Kalisher, Kim Kosai, V. Liquori, Valerie Randall, Joseph Rosbeck, Sanghamitra Sen, P. Wetzel, Maurice Halmos, Patrick Trotta, Andrew Hunter, John Jensen, Terence de Lyon, W. Johnson, B. Walker, Ward Trussel, Andy Hutchinson, Raymond Balcerak
HgCdTe APDs and APD arrays offer unique advantages for high-performance eyesafe LADAR sensors. These include: operation at room temperature, low-excess noise, high gain, high-quantum efficiency at eyesafe wavelengths, GHz bandwidth, and high-packing density. The utility of these benefits for systems are being demonstrated for both linear and area array sensors. Raytheon has fabricated 32 element linear APD arrays utilizing liquid phase epitaxy (LPE), and packaged and integrating these arrays with low-noise amplifiers. Typical better APDs configured as 50-micron square pixels and fabricated utilizing RIE, have demonstrated high fill factors, low crosstalk, excellent uniformity, low dark currents, and noise equivalent power (NEP) from 1-2 nW. Two units have been delivered to NVESD, assembled with range extraction electronics, and integrated into the CELRAP laser radar system. Tests on these sensors in July and October 2000 have demonstrated excellent functionality, detection of 1-cm wires, and range imaging. Work is presently underway under DARPA's 3-D imaging Sensor Program to extend this excellent performance to area arrays. High-density arrays have been fabricated using LPE and molecular beam epitaxy (MBE). HgCdTe APD arrays have been made in 5 X 5, 10 X 10 and larger formats. Initial data shows excellent typical better APD performance with unmultiplied dark current < 10 nA; and NEP < 2.0 nW at a gain of 10.
The objectives of the Integrated Imaging Sensors (I2S) Program are rtwofold. The first is to develop and deliver a rifle sight containing a single aperture and optical path for receiving, combining, and viewing radiation from the separate infrared (IR) and visible bands in a single image simultaneously. The second is to develop a sensor array sensitive in the radiation band spanning approximately from 0.4 μm to 1.7 μm by "fusing" indium-gallium-arsenic material onto silicon charge coupled devices. The ability to coincidentally and simultaneously form images from these two separate radiation bands is expected to significantly improve the detection and identification of objects from the case where only one radiation band is employed. Additionally, extending the cutoff of the visible band from 0.9 μm to 1.7 μm is expected to enhance viewing in this band as there is more available light, and further lessons the exacting requirement of desigining nearly noise free detectors.
Maurice Halmos, Michael Jack, James Asbrock, C. Anderson, Steven Bailey, George Chapman, E. Gordon, P. Herning, Murray Kalisher, Louis Klaras, Kim Kosai, V. Liquori, Mike Pines, Valerie Randall, Robin Reeder, Joseph Rosbeck, Sanghamitra Sen, Patrick Trotta, P. Wetzel, Andrew Hunter, John Jensen, T. DeLyon, Charlie Trussell, James Hutchinson, Raymond Balcerak
Raytheon has recently been funded by DARPA to develop an FPA for single shot eyesafe ladar operation. The goal of the program is to develop new high speed imaging rays to rapidly acquire high resolution, 3D images of tactical targets at ranges as long as 7 to 10 kilometers. This would provide precision strike, target identification from rapidly moving platforms, such as air-to-ground seekers, which would enhance counter-counter measure performance and the ability to lock-on after launch. Also a goal is to demonstrate the acquisition of hidden, camouflaged and partially obscured targets. Raytheon's approach consists of using HgCdTe APD arrays which offer unique advantages for high performance eyesafe LADAR sensors. These include: eyesafe operation at room temperature, low excess noise, high gain to overcome thermal and preamp noise, Ghz bandwidth and high packing density. The detector array will be coupled with a Readout Integrated Circuit, that will capture all the information required for accurate range determination. The two components encompass a hybrid imaging array consisting of two IC circuit chips vertically integrated via an array of indium metal 'bumps'. The chip containing the PAD detector array and the silicon signal processing readout chip are independently optimized to provide the highest possible performance for each function.
Laser radar systems are required for various military applications including obstacle detection, target recognition, and terrain mapping. Each application requires different system parameters such as pulse energy, repetition rate, and field of view. This paper presents a review of a multifunction laser radar system developed and tested for the Cooperative Eyesafe Laser Radar Program (CELRAP) of the U.S. Army CECOM Night Vision and Electronic Sensors Directorate.
Laser radar systems are required for various military applications including obstacle detection, target recognition, and terrain mapping. Each application requires different system parameters such as pulse energy, repetition rate, and field of view. This paper is the second in a series of papers describing the progress toward a multifunction laser radar system under construction for the Cooperative Eyesafe Laser Radar Program (CELRAP) of the U.S. Army CECOM Night Vision and Electronic Sensors Directorate.
Laser radar systems are required for various military applications including obstacle detection, target recognition, and terrain mapping. Each application requires different system parameters such as pulse energy, repetition rate, and field of view. This paper presents a review of a multifunction laser radar system under construction for the Cooperative Eyesafe Laser Radar Program (CELRAP) of the U.S. Army CECOM Night Vision and Electronic Sensors Directorate.
Terence de Lyon, B. Baumgratz, G. Chapman, E. Gordon, Andrew Hunter, Michael Jack, John Jensen, W. Johnson, Blaine Johs, Kim Kosai, W. Larsen, Greg Olson, M. Sen, Burt Walker
Separate absorption and multiplication avalanche photodiode (SAM-APD) device structures, operating in the 1.1 - 1.6 micrometer spectral range, have been fabricated in the HgCdTe material system by molecular-beam epitaxy. These HgCdTe device structures, which offer an alternative technology to existing III-V APD detectors, were grown on CdZnTe(211)B substrates using CdTe, Te, and Hg sources with in situ In and As doping. The alloy composition of the HgCdTe layers was adjusted to achieve both efficient absorption of IR radiation in the 1.1 - 1.6 micrometer spectral range and low excess-noise avalanche multiplication. To achieve resonant enhancement of hole impact ionization from the split-off valence band, the Hg1-xCdxTe alloy composition in the gain region of the device, x equals 0.73, was chosen to achieve equality between the bandgap energy and spin-orbit splitting. The appropriate value of this alloy composition was determined from analysis of the 300 K bandgap and spin-orbit splitting energies of a set of calibration layers, using a combination of IR transmission and spectroscopic ellipsometry measurements. MBE-grown APD epitaxial wafers were processed into passivated mesa-type discrete device structures and diode mini-arrays using conventional HgCdTe process technology. Device spectral response, dark current density, and avalanche gain measurements were performed on discrete diodes and diode mini- arrays on the processed wafers. Avalanche gains in the range of 30 - 40 at reverse bias of 85 - 90 V and array-median dark current density below 2 X 10-4 A/cm2 at 40 V reverse bias have been demonstrated.
SBRC is at the forefront of industry in developing IR focal plane arrays including multi-spectral technology and '3rd generation' functions that mimic the human eye. 3rd generation devices conduct advanced processing on or near the FPA that serve to reduce bandwidth while performing needed functions such as automatic target recognition, uniformity correction and dynamic range enhancement. These devices represent a solution for processing the exorbitantly high bandwidth coming off large area FPAs without sacrificing systems sensitivity. SBRC's two-color approach leverages the company's HgCdTe technology to provide simultaneous multiband coverage, from short through long wave IR, with near theoretical performance. IR systems that are sensitive to different spectral bands achieve enhanced capabilities for target identification and advanced discrimination. This paper will provide a summary of the issues, the technology and the benefits of SBRC's third generation smart and two-color FPAs.
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