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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Measurement of optical modulation functions in sparsely sampled mosaic focal plane arrays

It is pointed out that the measurement of optical modulation functions for detectors in focal plane arrays may be somewhat more difficult under 'full-up' systems conditions as compared to ideal laboratory conditions. An idealized optical modulation test arrangement is considered along with a full-up scanned system involving an earth mapper in polar orbit. In testing the system in full-up condition, a problem arises with respect to the acquisition of knife edge response data. In order to overcome this problem, a preferred method is developed for obtaining KER data on a single scan. A special 'phased edge' reticle is developed for use in the test set-up. Attention is given to aspects of knife edge reconstruction.

Young, J. B.↗
NASA NTRS1984

Focal depths and fault plane solutions of earthquakes and active tectonics of the Himalaya

Synthetic seismograms were compared with long-period body waves for nine earthquakes with epicenters in the Himalayan arc to determine depths of foci and to improve fault plane solutions. Focal depths are shallow (10-20 km). Inferred slip vectors are locally perpendicular to the mountain range; they plunge very gently (about 10 deg) in the eastern sections of the range and more steeply (about 25 deg) in western sections. Assuming India to be a rigid plate, the radially oriented slip vectors imply that southern Tibet extends at about half the rate of underthrusting in the Himalaya and therefore probably at about 5-10 mm/yr. The shallow depths and gentle dips of the fault planes, at least for the events in the eastern half of the range, are consistent with coherent underthrusting of the Indian plate beneath, at least, the Lesser Himalaya. The steeper dips of fault planes in the western part of the arc might reflect deformation of the overriding thrust plate or simply a steepening of the main underthrusting zone beneath the Greater Himalaya.

Baranowski, J.↗
NASA NTRS1985

Stress analysis of the space telescope focal plane structure joint

Two major efforts were begun concerning the Space Telescope focal plane structure joint. The 3-D solid finite element modeling of the bipod flexure plate was carried out. Conceptual models were developed for the load transfer through the three major bolts to the flexure plate. The flexure plate drawings were reconstructed using DADAM for the purpose of developing a file from which the coordinates of any point on the flexure plate could be determined and also to locate the attachment points of the various components which connect with the flexure plate. For modeling convenience the CADAM drawing of the flexure plate has been divided into several regions which will be subdivided into finite elements using MSGMESH, which is a finite element mesh generator available with MSC/NASTRAN. In addition to the CADAM work on the flexure plate, an effort was also begun to develop computer aided drawings of the peripheral beam which will be used to assist in modeling the connection between it and the flexure plate.

Foster, W. A., Jr.↗
NASA NTRS1983

Monolithic lead salt-silicon focal plane development

This paper is a summary of work done in the development of monolithic lead salt-silicon infrared focal plane technology. The photoconductive detector materials, PbS and PbSe are chemically deposited onto premetallized silicon MOSFET integrated circuit wafers. A variety of structures based on an implanted PMOS process were fabricated and evaluated. Operational results of an eight-element PbS array multiplexed on-chip are presented along with radiometric measurements on other integrated PbS-silicon MOSFET structures. PbS imagery is shown using one element of a 20-element array integrated on-chip.

Barrett, J. R.↗
NASA NTRS1983

Short wavelength infrared hybrid focal plane arrays

The employment of area focal plane arrays (FPA) has made it possible to obtain second generation infrared imaging systems with high resolution and sensitivity. The Short Wavelength Infrared (SWIR) region (1-2.5 microns) is of importance for imaging objects at high temperature and under conditions of reflected sunlight. The present investigation is concerned with electrooptical characterization results for 32 x 32 SWIR detector arrays and FPAs which are suitable for use in a prototype imaging spectrometer. The employed detector material is Hg(1-x)Cd(x)Te grown by liquid phase epitaxy on a CdTe transparent substrate. Attention is given to details of processing, the design of the detector array, the multiplexer, the fabrication of the hybrid FPA, and aspects of performance.

Vural, K.↗
NASA NTRS1984

Characterization of an advanced focal plane for multispectral linear array (MLA) application

It is pointed out that the MLA instrument represents the next generation in the Landsat series of earth resources satellites. The MLA sensor concept utilizes a pushbroom scan mode to eliminate electromechanical scan mirrors, and the lower reliabililty and higher power dissipation which accompany their employment. The pushbroom scanner makes use of a linear array which consists generally of thousands of detectors oriented perpendicular to the along-track direction of the satellite. Test techniques have been developed for the measurement of the module parameters which are critical to MLA focal plane performance. These measurements include the determination of infrared responsivity, linearity over the dynamic range, temporal noise, and fixed pattern effects on each detector element of each module tested. Tests related to spectral response, crosstalk, and spot scan profiles are also conducted. A description is provided of the test equipment involved.

King, P.↗
NASA NTRS1985

Design and performance of the cryogenic focal plane optics assembly for the Infrared Astronomical Satellite (IRAS)

The Infrared Astronomical Satellite (IRAS) has successfully completed its mission of providing an unbiased all-sky survey of astronomical objects in the 8 to 120 micrometer wavelength region. The design and performance of the Focal Plane Optics Assembly (FPOA) for the IRAS instrument is described in this paper. The FPOA consists of 62 survey field stops, 62 individual small field lenses, 124 small spectral filters, and a precision multi-part aluminum housing. The FPOA is capable of repeated thermal cycling from ambient temperature to 2 Kelvin. The spectral filters, along with the detector spectral responses, provide infrared bandpasses of 8-15, 18-30, 46-78, and 85-117 micrometers. The combination of very long wavelengths, liquid helium temperatures, and small size provided a significant design challenge. Spectral filter and field lens designs for the four spectral bands are described. Also, discussed are techniques which were developed for mechanical mounting of the small lenses and spectral filters, and to assure their optical alignment.

Bamberg, J. A.↗
NASA NTRS1984

MLA instruments and SWIR focal-plane technology

It is pointed out that next-generation sensors for earth observation will utilize Multispectral Linear Array (MLA) technology wherein linear detector arrays will scan the earth in pushbroom fashion. MLA instruments will permit a dramatic increase in detector dwell time, which can be utilized to improve spatial, spectral, and radiometric resolution. In connection with the considered applications for MLA sensors, the employed detector arrays should cover the visible, near-infrared, and shortwave infrared (SWIR) spectral bands. The present paper is mainly concerned with the development of mercury-cadmium-telluride focal-plane arrays for the SWIR spectral regime (1-2.5 microns). Attention is given to the requirements, design details regarding the detector array, the employed multiplexer technique, the hybrid concept, packaging, and the program status.

Brown, F. G.↗
NASA NTRS1986

SIRTF fine guidance sensor analysis - Focal plane configuration issues

The interrelationship of the issues of sensitivity, image centroiding precision, and field-of-view, and how they interact with the SIRTF pointing requirement to determine a fine guidance sensor focal plane configuration, are examined. While the examples are specifically oriented toward SIRTF, this approach is general and can be applied to other CCD-based star sensor systems.

Stier, Mark T.↗
NASA NTRS1987

Mercury cadmium telluride short- and medium-wavelength infrared staring focal plane arrays

Short and medium IR wavelength 64 x 64 hybrid focal plane arrays (FPAs) have been developed using sapphire-grown HgCdTe. The short wavelength arrays were developed for a prototype airborne imaging spectrometer, while those of medium wavelength are suitable for tactical missile seekers and strategic surveillance systems. Attention is presently given to results obtained for these FPAs' current-voltage characteristics, as well as for their characterization at different temperatures. The detector arrays were also mated to a multiplexer and characterized under different operating conditions. The unit cell size used is 52 x 52 microns.

Vural, Kadri↗
NASA NTRS1986

Test of the Hipparcos payload in the Liege vacuum facility focal

The Liege thermal vacuum optical bench (FOCAL) was used to control the mechanical stability of the structure of the European Space Agency's HIPPARCOS astrometry payload. The payload is designed to measure angles of .001 arcsec between stars during 2.5 years and this accuracy can only be reached with the extreme stability of the device. The structure of the payload is made of carbon fiber; it is thermally stabilized with an accuracy of .01 degrees C. During the test, the payload is enclosed in a shell made of shrouds having a geometry close to the shading structure of the spacecraft. The shroud temperatures are defined by the conditions in orbit, e.g., the spacecraft is spinning in front of the Sun with a period of two hours and the temperature of the shrouds is cycled around the payload with a 2 hour period. In order to avoid disturbances by vibrations, the payload is put on an adapter interfaced with the optical bench and the seismic block; the shrouds are supported by a carrier with no direct interface with the table. This method avoids perturbances brought about by the cooling fluid of the shrouds.

Jamar, C.↗
NASA NTRS1987

Matching a curved focal plane with CCD's - Wide field imaging of glancing incidence X-ray telescopes

The design of a wide field imaging camera suitable for use with a glancing incidence X-ray telescope is complicated by the sharply concave nature of the optimum focal surface of such a telescope. Such a camera made up of a mosaic of CCDs is being designed which is intended for flight aboard the Advanced X-ray Astrophysics Facility (AXAF). The design rationale and tradeoffs are discussed, and the layout for the imaging CCD array is presented. The related issue of optimizing performance of transmission objective gratings is also discussed, and the array of CCD orientations suitable for this problem is presented.

Nousek, J. A.↗
NASA NTRS1988

Improved optical performance near the butt regions of multichip focal planes

A technique for improving the optical characteristics at the butted edges of linear-multichip focal-plane imaging arrays is presented. It is shown that the air gap between butted imaging chips causes significant crosstalk. By filling the gap with a material that has an index of refraction more closely matched to that of the substrate, it is possible to reduce the optical crosstalk significantly.

Strong, R. T.↗
NASA NTRS1989

Blocked impurity band hybrid infrared focal plane arrays for astronomy

High-performance infrared hybrid focal plane arrays using 10- x 50-element Si:As blocked-impurity-band (BIB) detectors (cutoff wavelength = 28 microns) and matching switched MOSFET multiplexers have been developed and characterized for space astronomy. Use of impurity-band-conduction technology provides detectors which are nuclear-radiation-hard and free of the many anomalies associated with conventional silicon photoconductive detectors. Emphasis in the present work is on recent advances in detector material quality which have led to significantly improved detector and hybrid characteristics. Results demonstrating increased quantum efficiency (particularly at short-wavelength infrared), obtained by varying the BIB detector properties (infrared active layer thickness and arsenic doping profile), are summarized. Measured read noise and dark current for different temperatures are reported. The hybrid array performance achieved demonstrates that BIB detectors are well suited for use in astronomical instrumentation.

Reynolds, D. B.↗
NASA NTRS1989

CCD TV focal plane guider development and comparison to SIRTF applications

It is expected that the SIRTF payload will use a CCD TV focal plane fine guidance sensor to provide acquisition of sources and tracking stability of the telescope. Work has been done to develop CCD TV cameras and guiders at Lick Observatory for several years and have produced state of the art CCD TV systems for internal use. NASA decided to provide additional support so that the limits of this technology could be established and a comparison between SIRTF requirements and practical systems could be put on a more quantitative basis. The results of work carried out at Lick Observatory which was designed to characterize present CCD autoguiding technology and relate it to SIRTF applications is presented. Two different design types of CCD cameras were constructed using virtual phase and burred channel CCD sensors. A simple autoguider was built and used on the KAO, Mt. Lemon and Mt. Hamilton telescopes. A video image processing system was also constructed in order to characterize the performance of the auto guider and CCD cameras.

Rank, David M.↗
NASA NTRS1989

Optimal focal-plane restoration

Image restoration can be implemented efficiently by calculating the convolution of the digital image and a small kernel during image acquisition. Processing the image in the focal-plane in this way requires less computation than traditional Fourier-transform-based techniques such as the Wiener filter and constrained least-squares filter. Here, the values of the convolution kernel that yield the restoration with minimum expected mean-square error are determined using a frequency analysis of the end-to-end imaging system. This development accounts for constraints on the size and shape of the spatial kernel and all the components of the imaging system. Simulation results indicate the technique is effective and efficient.

Reichenbach, Stephen E.↗
NASA NTRS1988

A 256 by 256 HgCdTe hybrid focal plane for low-background earth resources and astronomy applications

This paper describes a 256 x 256 HgCdTe hybrid focal plane with a 0.9- to 2.6-micron spectral range. The silicon FET switch multiplexer (mux) is based on previous hybrid work with a 128 x 128 Reticon mux. The high-density device described has a 40-micron pixel pitch vs 60-micron pixel pitch for the 128 x 128 devices. A read noise of about 1,000 e(-) has been obtained on developmental hybrid structures, along with full well capacities of about 1 x 10 to the 6th e(-). Preliminary device characterization for the 256 x 256 device, along with the first low-background astronomy test results for the 128 x 128 devices, will be presented.

Bailey, Gary C.↗
NASA NTRS1989

Study of the polarization dependence of the photoelectric effect in the soft X-ray band - A focal plane photoelectric stellar X-ray polarimeter for the Spectrum-X-Gamma mission

An experimental study of the polarization dependence of the photoelectric effect in cesium iodide in the soft X-ray band was started (Heckler et al., 1989). At a grazing angle of 10 degrees and a photon energy of 2.6 keV, it is found that the photoelectric yield from a thin layer of evaporated cesium iodide varies by 12.4 percent as the polarization vector of the incident X-ray beam is rotated about the line-of-sight. The rotation angle corresponding to the maximum photoyield is displaced by 16 degrees from the normal to the photocathode. This modulation and phase shift are in good agreement with the results recently reported by Fraser, et al. (1989) It is shown that a focal plane stellar X-ray polarimeter based on this photoelectric effect will be substantially more efficient than convential X-ray polarimeters such as those based on either Bragg reflection or scattering from low atomic number targets.

Heckler, A.↗