Robert J. Martineau

Cassini infrared Fourier spectroscopic investigation

The composite infrared spectrometer (CIRS) is a remote sensing instrument to be flown on the Cassini orbiter. CIRS will retrieve vertical profiles of temperature and gas composition for the atmospheres of Titan and Saturn, from deep in their tropospheres to high in their stratospheres. CIRS will also retrieve information on the thermal properties and composition of Saturns rings and Saturnian satellites. CIRS consists of a pair of Fourier Transform Spectrometers (FTSs) which together cover the spectral range from 10-1400 cm-1 with a spectral resolution up to 0.5 cm-1. The two interferometers share a 50 cm beryllium Cassegrain telescope. The far-infrared FTS is a polarizing interferometer covering the 10-600 cm-1 range with a pair of thermopile detectors, and a 3.9 mrad field of view. The mid-infrared FTS is a conventional Michelson interferometer covering 200-1400 cm-1 in two spectral bandpasses: 600-1100 cm- 1100-1400 cm(superscript -1 with a 1 by 10 photovoltaic HgCdTe array. Each pixel of the arrays has an approximate 0.3 mrad field of view. The HgCdTe arrays are cooled to approximately 80K with a passive radiative cooler.

Detectors for the James Webb Space Telescope Near‐Infrared Spectrograph. I. Readout Mode, Noise Model, and Calibration Considerations

We describe how the James Webb Space Telescope (JWST) Near-Infrared Spectrographs (NIRSpec) detectors will be read out, and present a model of how noise scales with the number of multiple nondestructive reads sampling up the ramp. We believe that this noise model, which is validated using real and simulated test data, is applicable to most astronomical near-infrared instruments. We describe some nonideal behaviors that have been observed in engineering-grade NIRSpec detectors, and demonstrate that they are unlikely to affect NIRSpec sensitivity, operations, or calibration. These include a HAWAII-2RG reset anomaly and random telegraph noise (RTN). Using real test data, we show that the reset anomaly is (1) very nearly noiseless and (2) can be easily calibrated out. Likewise, we show that large-amplitude RTN affects only a small and fixed population of pixels. It can therefore be tracked using standard pixel operability maps.

Detectors for the James Webb Space Telescope near infrared spectrograph (NIRSpec)

The Near Infrared Spectrograph (NIRSpec) will be the James Webb Space Telescopes (JWSTs) primary near-infrared spectrograph. NIRSpec is a multi-object spectrograph with fixed-slit and integral field modes. EADS/Astrium is building NIRSpec for the European Space Agency (ESA), with NASA is providing the detector subsystem and programmable multi-aperture mask. In this paper, we summarize recent progress on the detector subsystem including tests demonstrating that JWSTs Rockwell HAWAII-2RG sensor chip assemblies have achieved Technology Readiness Level 6 (TRL-6). Achieving TRL-6 is an important milestone because TRL-6 is required for flight.

Large format HgCdTe arrays for the James Webb Space Telescope

The near infrared spectrograph (NIRSpec) will be the James Webb Space Telescopes (JWSTs) primary near-infrared spectrograph. NIRSpec is a multi-object spectrograph with fixed-slit and integral field modes. EADS/Astrium is building NIRSpec for the European Space Agency (ESA), with NASA providing the detector subsystem and programmable multi-aperture mask. In this presentation we present an overview of the detector subsystem (DS)

Detector requirements for NGST

This paper summarizes the findings of the Next Generation Space Telescope (NGST) Detector Requirements Review Panel. This panel was comprised of NGST Integrated Science Instrument Module study representatives, detector specialists, and members of the NGST project science team. It has produced a report that recommends detector performance levels, and has provided rationale for deriving these levels from basic, anticipated NGST science goals and programs. Key parameters such as detector array format, quantum efficiency, and noise are discussed and prioritized.

PC detector passivation for high performance

Probably the most important factor in producing HgCdTe detectors of high performance is surface passivation. A good passivant for PC HgCdTe detectors accumulates the surface thereby reflecting minority carriers from surface imperfections and increasing minority carrier lifetime. A variety of passivants are known and used to various degrees, including sulfides, fluorides, oxides, and others. One of the problems with known passivants is that they tend to accumulate the surface too strongly, thus producing non-optimal results. We have developed a new passivation process which passivates the surface without strong accumulation. This results in detector resistance that is about 50%higher than that achieved with traditional KOH passivation, responsivities that are from 100 to 200% higher, and detectivities that are from 50to 100% higher for long wavelength devices. Materials and processing details used to achieve these results, as well as experimental data will be presented. Keyword: passivation, infrared, HgCdTe, detector

HgCdTe detector technology and performance for the Composite Infrared Spectrometer (CIRS)/Cassini mission

The composite infrared spectrometer (CIRS) instrument, an important component of the Cassini mission, consists of 3 focal plane arrays for sensing IR radiation of the Saturnian planetary system. Goddard Space Flight Center has fabricated, tested, and delivered high performance, 10- element HgCdTe photoconductive (PC) arrays for use on CIRS FP3, the focal plane responsible for detection of radiation in the 9.1 to 16.7 micrometers spectral band. The delivered flight array has peak responsivity 100 percent above CIRS specification, detectivity 30 percent or more above specification, and a cutoff wavelength of 17.3 micrometers at the operating temperature of 80 K. In order to achieve high performance at low frequency while maintaining limited power dissipation, we adopted a split-geometry detector structure. This design also ensured the buttability of the PC arrays to photovoltaic arrays supplied by CE-Saclay-France for detection of radiation in the 7.1 to 9.1 micrometers range. The detector structure is also noteworthy for its use of 0.05 micrometers Alumina powder-loaded epoxy to minimize reflection at the epoxy/HgCdTe interface, thus spoiling undesired optical resonance. This was done in order to meet the CIRS spectral uniformity requirement, which would have been difficult at these long wavelengths without this feature.

High-performance HgCdTe infrared detectors for the GOES long-wave sounder

GOES long wave sounder (LWS) detector requirements have always pushed the state-of-the-art for longwave detectors operating in the vicinity of 102 K. Performance and yield of acceptable detectors have always been problems and continue to be important issues affecting the performance of instruments of both present and future design. GSFC has been examining new device and operational concepts aimed at producing significant improvements in performance and yield. Our approach has been directed towards mitigating the deleterious effects of operating small geometry HgCdTe PC devices under heavy bias, that is, under minority carrier sweepout, as is typical in conventional LWS detector operation. Specifically, theory indicates that detectors of the new design operating under optimal bias conditions have significantly higher responsivity, lower power dissipation,and lower 1/f noise knees than conventional LWS detectors. In this paper we will describe the new LWS detectors fabricated at GSFC, present detector data, and review the theory of operation of these devices.

Split-geometry detectors, our eyes in space

Infrared detectors have projected our ability to explore our planet and our solar system far beyond the spatial, temporal, and spectral limitations of our natural vision. As such, they are our eyes in space, constantly searching the heavens, and sending back information about the origin, constitution, and dynamics of planetary atmospheres, and other processes of interest. Their ability to do this effectively depends on their sensitivity. Today, long wave PC (photoconductive) HgCdTe detectors are the detectors of choice for applications requiring high sensitivity at long wavelengths and elevated temperature. However, planetary exploration and space surveillance of the earth’s climatic condition are presently still limited by the sensitivity of available detectors. This paper will describe detectors developed at Goddard to provide enhanced performance for applications such as the CIRS/Cassini mission to Saturn and Titan, and the GOES weather satellite. Specifically, this paper will show theoretically and experimentally how detectors of split-geometry design can be exploited to increase detector resistance, responsivity, and detectivity, while decreasing 1/f noise and power dissipation. Photomicrographs of split-geometry detectors will be shown, and data demonstrating theoretical split-geometry design advantages will be presented for flight arrays built for the CIRS/Cassini mission, and for advanced detectors for GOES.

Advanced Geosynchronous Studies Imager: focal plane design

A focal plane system to generate images in 18 spectral channels ranging from visible to long-wave IR has been designed for the AGSI. The system is a line scan imager, comprised for four focal planes populated with linear detector arrays optimized for operating in the various AGSI spectral regions. Light from the AGSI telescope is diverted to the focal planes by spectrally tuned dichroic beam splitters. At the focal planes narrowband interference filters placed in close proximity to the detector arrays further filter the light. Multispectral silicon CCDs are used for visible and near IR channels. Key to system performance is the ability to use time delay and integration (TDI) in some of the narrower or less photon rich spectral channels. Detector arrays are supported by highly modular and therefore flexible and low risk signal processing and control circuits. Performance predictions have been generated for all of the spectral channels and show that the focal planes will meet or exceed NASAs requirements for an advanced imaging observatory to observe weather and climate processes and NOAAs requirements for an advanced GOES imager.