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Results for “Long-wavelength Infrared”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
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NASA NTRS1990

Long-wavelength infrared detection in a Kastalsky-type superlattice structure

The first successful demonstration of long-wavelength infrared (LWIR) detection with a Kastalsky-type AlGaAs/GaAs superlattice structure is reported. The experimental response band of the detector is centered near 10 microns in very good agreement with the theoretical response band provided that electron-electron interactions are taken into account. The detector operates at significantly lower bias voltage than photoconductive multiple quantum well LWIR detectors. This could lead to important advantages in applications to photovoltaic detector arrays. The response at 83 K is about 50 percent of the response at 24 K.

Byungsung, O.↗
NASA NTRS1989

Long-Wavelength Infrared Detector

Proposed device detects infrared photons of 10- to 100-micrometer wavelength by intersubband absorption in coupled quantum wells. Based on splitting of energy level occuring when two quantum wells placed so close together wave functions of quantized energy levels overlap. Detector absorbs photons, energy which equals difference in energy between two levels resulting from split. Because degree of overlap of wave functions and, therefore, magnitude of split varied by varying width of barrier between two coupled wells, such detector, in principle, designed to operate at any desired wavelength. Restrictions on design parameters of quantum wells of proposed device less severe than single-well devices. Energy levels near tops of wells still necessary so photoexcited carriers tunnel out. Additional flexibility in design obtained by use of wells formed by barriers of different heights.

Vasquez, Richard P.↗
NASA NTRS1990

Superlattice Long-Wavelength Infrared Sensors

Superlattice of LaN and Si detects at wavelengths up to 12 micrometers. If LaN grown epitaxially on silicon, sensitivity of silicon-based photodetectors extended farther into infrared wavelength region with high quantum detection efficiency by use of LaN/Si superlattices. In principle, by appropriate choice of thicknesses of layers, effective band-gap energy of superlattice structure set to any desired value between band gaps of two materials.

Fathauer, Robert W.↗
NASA NTRS1990

Novel Si(1-x)Ge(x)/Si heterojunction internal photoemission long-wavelength infrared detectors

The feasibility of a novel p(+)-Si(1-x)Ge(x)-p-Si heterojunction internal photoemission (HIP) IR detector is demonstrated. A degenerately doped p(x)-Si(1-x)Ge(x) layer is required for strong IR absorption to generate photoexcited holes. The Si(1-x)Ge(x) layers are grown by molecular beam epitaxy, with boron concentrations up to 10 to the 20th/cu cm achieved by using an HBO2 source. Photoresponse at wavelengths ranging from 2 to 10 microns has been obtained with quantum efficiencies above 1 percent. The tailorable cutoff wavelength of the HIP detector has been demonstrated by varying the Ge composition ratio in the Si(1-x)Ge(x) layers.

Lin, T. L.↗
NASA NTRS1978

Low background focal plane array testing in the far infrared

A new long-wavelength infrared test facility is being developed to conduct proof-of-performance tests of focal plane arrays for the Infrared Astronomical Satellite (IRAS) telescope. This facility is believed to be unique in that it will calibrate full-sized arrays designed for the 5-120-micron region of the IR spectrum under simulated spaceflight conditions and at background levels as low as 8 million photons/sq cm-sec. Most of the tests will be performed in a main test chamber which contains a liquid helium shroud, blackbody sources, an arrangement to simulate zodiacal background, and spot scanning optics. A noncontaminating high-vacuum pumping system will be used to evacuate the chamber prior to cool-down to prevent molecular deposition. All housekeeping and focal plane signal outputs are multiplexed, digitized, and transmitted on high-speed data lines to a PDP-11/70 computer. The computer provides real-time displays on a color CRT terminal and stores data for subsequent reduction and hard copy output. An overview of the conceptual design and performance specifications of the test facility are given.

Iufer, E. J.↗
NASA NTRS1990

Photovoltaic quantum well infrared photodetectors

Quantum well infrared photodetectors (QWIP) are a promising new approach to long-wavelength infrared detector arrays. Both single-well photovoltaic and multiple-well photoconductive devices have been demonstrated. The author discusses noise considerations as they apply to photovoltaic devices, grating coupling of the infrared light into QWIPs, and recently demonstrated electrically tunable detectors. The use of light trapping to enhance the quantum efficiency and reduce cross-talk in an array is addressed.

Lyon, Steve A.↗
NASA NTRS1990

Infrared properties of nearby radio galaxies

The IRAS data for a sample of nearby radio galaxies (z less than 0.13) are analyzed. Comparison of the infrared, radio, and optical data suggests that most of the long-wavelength infrared emission comes from cool interstellar dust for almost all of the galaxies; these galaxies may contain large amounts (10 to the 8th - 10 to the 10th solar masses of interstelar matter. About 15 percent of the galaxies show evidence for a hotter thermal component emitting at the shorter IRAS wavelengths; this could be due to dust in the inner regions of the galaxy heated by the active galactic nucleus.

Knapp, G. R.↗
NASA NTRS1990

Intersubband absorption in Si(1-x)Ge(x/Si superlattices for long wavelength infrared detectors

Researchers calculated the absorption strengths for intersubband transitions in n-type Si(1-x)Ge(x)/Si superlattices. These transitions can be used for the detection of long-wavelength infrared radiation. A significant advantage in Si(1-x)Ge(x)/Si supperlattice detectors is the ability to detect normally incident light; in Ga(1-x)Al(x)As/GaAs superlattices, intersubband absorption is possible only if the incident light contains a polarization component in the growth direction of the superlattice. Researchers present detailed calculation of absorption coefficients, and peak absorption wavelengths for (100), (111) and (110) Si(1-x)Ge(x)/Si superlattices. Peak absorption strengths of about 2000 to 6000 cm(exp -1) were obtained for typical sheet doping concentrations (approx. equals 10(exp 12)cm(exp -2)). Absorption comparable to that in Ga(1-x)Al(x)As/GaAs superlattice detectors, compatibility with existing Si technology, and the ability to detect normally incident light make these devices promising for future applications.

Rajakarunanayake, Yasantha↗
NASA NTRS1988

A survey of IRAS data on 41 classical novae

The IRAS database has been searched for detections of 41 classical novae using coadditions of survey scans; 15 were detected. IRAS temporal observations of novae in outburst are discussed. The observed long-wavelength infrared distributions of DQ Her, and possibly HR Del, can be explained by emission from small (a of about 0.1 microns) dust grains heated by the central object. An alternative explanation for the energy distributions of DQ Her and HR Del is emission from fine-structure lines. FH Ser and LW Ser display energy distributions that have color temperatures much too hot to be due to heating of dust by the central source in any plausible scenario. Line emission is probably the best explanation of their observed energy distributions. The novae NQ Vul and LV Vul have energy distributions that may be contaminated by emission from galactic cirrus. The unusual object PL 1547.3-5612 exhibits an energy distribution that does not resemble those of planetary nebulae or other novae detected in this sample. An IRAS low-resolution spectrum of RR Tel shows the 10-micron silicate emission feature.

Harrison, T. E.↗
NASA NTRS1987

Long-wavelength absorption by fractal dust grains

The far-infrared and submillimeter absorption properties of random aggregates of conducting spheres have been studied as a possible source for the long-wavelength absorption of interstellar dust grains. The complex shapes of random aggregates have various fractal dimensions, depending on the process that forms them. The long wavelength absorption versus frequency is affected more by the shape of a conducting grain than by its composition.

Wright, Edward L.↗
NASA NTRS1990

Optimal sampling and sensitivity limits of integrating detector arrays in a space environment

The performance of integrating detectors with either destructive read-out or nondestructive direct read-out in a space environment subject to charge-particle and radiation hits was investigated by determining the optimal integration time for maximizing the performance in the presence of a given hit rate. The performance relative to that expected for background-limited performance was evaluated using a combination of analytic techniques and Monte Carlo simulations. Results are used to estimate the performance degradation, due to cosmic rays, of the long-wavelength spectrometer of the Space Infrared Telescope Facility. It was found that its performance may be a factor of 1-5 worse than the background limited performance.

Herter, T.↗
NASA NTRS1974

Visual and infrared observations of late-type supergiants in the southern sky

Spectral types and photometry ranging from 0.4 to 18 microns are given for 54 late-type stars, including 21 supergiants. The infrared observations of the supergiants confirm the dependence of the strength of the 10-micron silicate emission feature on the spectral type and luminosity class of the star. The long-wavelength data are also used to determine the interstellar extinction by fitting an appropriate blackbody to the infrared observations. The deviation from the blackbody at the shorter wavelengths is then attributed to interstellar absorption and absorption by TiO. This method is particularly useful when the short-wavelength photometry is contaminated by a close companion. The M supergiant AH Sco has excess radiation between 1.5 and 8 microns similar to the NML Tauri-type infrared stars. This excess energy resembles free-free emission.

Humphreys, R. M.↗
NASA NTRS1984

Conceptual design of a hybrid Ge:Ga detector array

For potential applications in space infrared astronomy missions such as the Space Infrared Telescope Facility and the Large Deployable Reflector, integrated arrays of long-wavelength detectors are desired. The results of a feasibility study which developed a design for applying integrated array techniques to a long-wavelength (gallium-doped germanium) material to achieve spectral coverage between 30 and 200 microns are presented. An approach which builds up a two-dimensional array by stacking linear detector modules is presented. The spectral response of the Ge:Ga detectors is extended to 200 microns by application of uniaxial stress to the stack of modules. The detectors are assembled with 1 mm spacing between the elements. Multiplexed readout of each module is accomplished with integration sampling of a metal-oxide-semiconductor (MOS) switch chip. Aspects of the overall design, including the anticipated level of particle effects on the array in the space environment, a transparent electrode design for 200 microns response, estimates of optical crosstalk, and mechanical stress design calculations are included.

Parry, C. M.↗
NASA NTRS1990

The nature of unidentified 12 micron IRAS sources at high Galactic latitudes

A sample of 47 previously uncatalogued objects located above a Galactic latitude of 50 deg, and detected at 12 microns by the IRAS, is studied using near-infrared photometry. Ground-based observations show that the objects consist primarily of late-type M giant stars with long-wavelength excesses probably due to emission from dust associated with mass loss. The sample contains one oxygen-rich giant star undergoing rapid mass loss; an extremely cool (1230 K) carbon star 12560-1656 that may be as far as 10 kpc away; and a luminious quasar 13349-2438. The absence of nearby, low-luminosity infrared sources in this sample limits the space density of field brown dwarf stars. The fact that almost all the IRAS 12 micron sources have stellar counterparts visible on both the red and blue Palomar Observatory Sky Survey prints provides a tool for discriminating ordinary red stars.

Beichman, C. A.↗
NASA NTRS1988

Development of a unit cell for a Ge:Ga detector array

Two modules of gallium-doped germanium (Ge:Ga) infrared detectors with integrated multiplexing readouts and supporting drive electronics were designed and tested. This development investigated the feasibility of producing two-dimensional Ge:Ga arrays by stacking linear modules in a housing capable of providing uniaxial stress for enhanced long-wavelength response. Each module includes 8 detectors (1x1x2 mm) mounted to a sapphire board. The element spacing is 12 microns. The back faces of the detector elements are beveled with an 18 deg angle, which was proved to significantly enhance optical absorption. Each module includes a different silicon metal-oxide semiconductor field effect transistor (MOSFET) readout. The first circuit was built from discrete MOSFET components; the second incorporated devices taken from low-temperature integrated circuit multiplexers. The latter circuit exhibited much lower stray capacitance and improved stability. Using these switched-FET circuits, it was demonstrated that burst readout, with multiplexer active only during the readout period, could successfully be implemented at approximately 3.5 K.

Source record↗
NASA NTRS1976

The anomalous thermal properties of glasses at low temperatures

While experimentally there is great regularity below 1 deg K in the behavior of a particular thermal property for all amorphous dielectrics it is not understood why these properties should differ from those of crystalline dielectrics, since it would seem that at low temperatures long-wavelength elastic waves, similar in both cases, would determine the thermal properties. A model involving systems having very few levels is used in the present study, although the relation between the model's systems and the nature of the glassy state is not known. It is shown, among other effects, that: specific heat measurements above 0.1 K indicate a distribution of local modes independent of energy; ultrasonic velocity measurements give information about phonon-local mode coupling parameters; and thermal expansion and far infrared experiments indicate a phonon-assisted tunneling model.

Pohl, R. O.↗
NASA NTRS1977

Infrared observations of Nova Cygni 1975

Infrared photometry from 1 to 20 microns and spectroscopy at about 2 microns are presented for Nova Cygni 1975 for the period from 2 days before to 1 yr after maximum light. The data can be explained by a simple model in which the expanding gas expelled during the explosion is always a plasma at approximately 10,000 K. Initially the gas is optically thick; this phase clearly defines the time of onset of the nova. Later, as the gas continues to expand, it becomes optically thin. The temporal dependence of the observed flux suggests that in this phase the expanding cloud is in the form of a shell. After about 300 days, long-wavelength emission which may be attributable to thermal reradiation from dust is observed.

Ennis, D.↗
NASA NTRS1974

Titan - Unidentified strong absorptions in the photometric infrared

The morphology of Titan's infrared spectral features reveals a pattern of differences with respect to Saturn's bands. Titan's bands exhibit a progressive washing out with increasing wavelength relative to the corresponding bands in Saturn's spectrum. Unidentified absorption features of apparently gaseous origin appear in the long-wavelength wing of Titan's 1-micron CH4 band complex with considerably greater strength. Greater absorption is also observed in the 1.1 micron region. Not all of the phenomena can be explained by enhanced CH4 absorption, so Titan's spectrum implies the existence of another spectroscopically active gas. Several candidates for this gas are briefly considered.

Trafton, L.↗