Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “submillimeter”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Far-infrared selected star formation regions

Detailed far-IR observations and complementary submillimeter, 5 GHz continuum and C(O-18) observations of a sample of eight far-IR selected luminous regions of star formation are presented. The observations show that the sources of luminosity coincide with density peaks in the molecular clouds and that the exciting stars lie deep within these condensations. The far-IR sources have diversely shaped 40-180 micron spectra even though their 60-100 micron color temperatures are similar. The radio and far-IR results together show that the exciting stars are in clusters containing either zero-age main-sequence and pre-main-sequence stars or consisting entirely of pre-main-sequence objects. C(O-18) and submillimeter observations imply gas densities approximately 100,000-high enough to make T(dust) approximately T(gas).

Harper, D. A.↗
NASA NTRS1984

A 150 Micron Heterodyne Spectrometer for Airborne Astronomy

The advantages of heterodyne detection for high resolution spectroscopy were long known to radio astronomers. Heterodyne spectroscopy was productive at submillimeter wavelengths, but its extension to shorter submillimeter and far-infrared (FIR) wavelengths was hampered by inadequate mixers and local oscillators. A significant advance in FIR receiver technology was demonstrated using an optically-pumped FIR laser and a Schottky-diode mixer. Any similar spectrometer intended for airborne observations at shorter wavelengths must be compatible with the more restrictive aircraft environment. The effectiveness of the design of a FIR heterodyne spectrometer was verified in ground-based observations with a prototype version. The airborne successor is even more compact, and has a much broader spectral coverage. Flight tests are scheduled for the new instrument.

Betz, A.↗
NASA NTRS1987

Deep, Precise Etching in Semiconductors

Semiconductors made to accept precise etching after pretreatment. Combination of material destabilization and anisotropic etching permits formation of precise perpendicular-wall cavities in silicon wafers and other semiconductors. New technique extends capabilities of current micromachining technology to fabrication of submillimeter waveguide arrays and filters. Pre-etching process currently used to fabricate thin-walled arrays of submillimeter waveguides for use as dichroic bandpass filters. Possible applications include integration of sensor probes and processing of circuitry on same silicon chip.

Shlichta, P. J.↗
NASA NTRS1986

The Large Deployable Reflector (LDR) report of the Science Coordination Group

The Large Deployable Reflector (LDR) is a telescope designed to carry out high-angular resolution, high-sensitivity observations at far-infrared and submillimeter wavelengths. The scientific rationale for the LDR is discussed in light of the recent Infrared Astronomical Satellite (IRAS) and Kuiper Airborne Observatory (KAO) results and the several new ground-based observatories planned for the late 1980s. The importance of high sensitivity and high angular resolution observations from space in the submillimeter region is stressed. The scientific and technical problems of using the LDR in a light bucket mode at approx. less than 5 microns and in designing the LDR as an unfilled aperture with subarcsecond resolution are also discussed. The need for an aperture as large as 20 m is established, along with the requirements of beam-shape stability, spatial chopping, thermal control, and surface figure stability. The instrument complement required to cover the wavelength-spectral resolution region of interest to the LDR is defined.

Source record↗
NASA NTRS1988

The rotational spectrum of nitric acid - The first five vibrational states

The details of work on the nu(8) vibrational state, which arise from the NO2 out-of-plane vibration, are reported. For this state, over 210 transitions have been measured in the millimeter and submillimeter spectral region and analyzed with Watson's A-reduced centrifugal distortion Hamiltonian. Also included in this work is a comparison of all these spectra and an overview of the millimeter and submillimeter spectra associated with these states. Although at the high sensitivity available in laboratory experiments, many additional lines are observable, all arise from vibrational states whose populations are more than 100 times lower than the ground state. The most prominent of these are due to the states which give rise to the perturbed 2 nu(9) and nu(5) bands near 11 microns. These results provide a significant data base for both atmospheric remote sensing experiments and spectral analyses of data in other spectral regions, especially the IR.

Crownover, Richard L.↗
NASA NTRS1988

Sensors research and technology

Information on sensors research and technology is given in viewgraph form. Information is given on sensing techniques for space science, passive remote sensing techniques and applications, submillimeter coherent sensing, submillimeter mixers and local oscillator sources, non-coherent sensors, active remote sensing, solid state laser development, a low vibration cooler, separation of liquid helium and vapor phase in zero gravity, and future plans.

Cutts, James A.↗
NASA NTRS1989

Extragalactic radiation and the ultra-high-energy cosmic-ray spectrum

The effect of extragalactic microwave and submillimeter-radiation fields on the ultrahigh-energy cosmic-ray spectrum is reexamined. It is found that the general characteristics of the spectrum can be derived from fairly simple analytical arguments. It is shown that the various spectral features obtained by numerical calculations can be explored by simpler and more general means. This approach is illustrated using a newly derived lifetime-energy relation based on the new submillimeter observations.

Stecker, F. W.↗
NASA NTRS1990

Contribution of cool dust to the FIR brightness distribution of NGC 6946 Sc(s)2

A few galaxies have been observed at submillimeter wavelengths (Stark et al., 1988; Eales, Wynn-Williams, and Duncan, 1988). These observations do not support the hypothesis that there exist substantial amounts of cool dust generating submillimeter radiation in excess of predictions from modified blackbody curves of the form (1/lambda)exp 1.5 B sub v (v, T) fit to total 100 and 160 micron fluxes. However, researchers find relatively cold dust (approx. 17 to 23 degrees K) at several interarm locations in the central 5 minute by 5 minute region of NGC 6946 Sc(s)II. Since molecular gas is the predominate constituent of the interstellar medium (ISM) in this region, such low dust temperatures are indicative of quiescent molecular clouds and low star formation rates. Based on the contribution of cool grains to the 160 micron surface brightness distribution, regions of low star formation activity can be identified. A 1/lambda exp 1.5 emissivity law is assumed for this analysis. Researchers assumed a two temperature grain model in an effort to decompose the far infrared surface brightness distribution of NGC 6946 into contributions from cool, quiescent and active, star forming regions. This model has some validity; although an oversimplification of the dust energetics, researchers find from it that, where giant HII regions are sparse, a significant fraction of the 160 micron emission is emitted by a cool grain component which the Infrared Astronomy Satellite (IRAS) could barely detect.

Engargiola, Greg↗
NASA NTRS1990

Silicates and variability in comets Okazaki-Levy-Rudenko (1989r) and Austin (1989c1)

Comet Okazaki-Levy-Rudenko (1989r) was studied over a wide range of wavelengths from the UV to the submillimeter. Using visual magnitude estimates from the IAU Circulars and reported submillimeter fluxes in conjunction with the thermal infrared spectroscopy and filter photometry, the nature of the grains and the behavior of the comet can be assessed and compared to other comets studied under this program. In addition, preliminary results from a collaborative infrared study of Comet Austin are presented which address the nature of the dust in that comet. Progress on a model for cometary properties and brightness behavior is discussed.

Russell, Ray W.↗
NASA NTRS1991

Submicron area NbN/MgO/NbN tunnel junctions for SIS mixer applications

The development of submicron area mixer elements for operation in the submillimeter wave range is discussed. High-current-density NbN/MgO/NbN tunnel junctions with areas down to 0.1 sq microns have been fabricated in both planar and edge geometries. The planar junctions were fabricated from in situ deposited trilayers using electron-beam lithography to pattern submicron area mesas. Modifications of fabrication techniques used in larger-area NbN tunnel junctions are required and are discussed. The NbN/MgO/NbN edge junction process using sapphire substrates has been transferred to technologically important quartz substrates using MgO buffer layers to minimize substrate interactions. The two junction geometries are compared and contrasted in the context of submillimeter wave mixer applications.

Leduc, H. G.↗
NASA NTRS1992

Barrier/n/n+ Varactor Frequency Multipliers

Barrier/n/n+ (BNN+) varactor diodes developed as frequency multipliers at millimeter and submillimeter wavelengths. Devices required to serve as frequency triplers or quintuplers to provide powers of order of milliwatts at frequencies from 0.1 THz to about 1 THz. Feature Mott or heterojunction barriers and back-to-back diode configuration, which make it possible to obtain symmetrical capacitance-versus-voltage characteristics with high ratio between maximum and minimum capacitances. Extension of barrier/intrinsic/n+ (BIN+) concept described in "BIN Diode for Submillimeter Wavelengths" (NPO-17258).

Lieneweg, Udo↗
NASA NTRS1991

The Next Century Astrophysics Program

The Astrophysics Division within the NASA Office of Space Science and Applications (OSSA) has defined a set of major and moderate missions that are presently under study for flight sometime within the next 20 years. These programs include the: Advanced X Ray Astrophysics Facility; X Ray Schmidt Telescope; Nuclear Astrophysics Experiment; Hard X Ray Imaging Facility; Very High Throughput Facility; Gamma Ray Spectroscopy Observatory; Hubble Space Telescope; Lunar Transit Telescope; Astrometric Interferometer Mission; Next Generation Space Telescope; Imaging Optical Interferometer; Far Ultraviolet Spectroscopic Explorer; Gravity Probe B; Laser Gravity Wave Observatory in Space; Stratospheric Observatory for Infrared Astronomy; Space Infrared Telescope Facility; Submillimeter Intermediate Mission; Large Deployable Reflector; Submillimeter Interferometer; and Next Generation Orbiting Very Long Baseline Interferometer.

Swanson, Paul N.↗
NASA NTRS1992

A 200 GHz tripler using single barrier varactor

The GaAs Schottky varactor diode is the nonlinear device most commonly used for submillimeter wave harmonic generation. Output power adequate to serve as a local oscillator source for SIS tunnel junctions has been demonstrated with whisker-contacted GaAs Schottky varactor multipliers in waveguide mounts up to about 800 GHz. In this paper, we present results for a tripler to 200 GHz using a new multiplier device, the single barrier varactor (SBV). This new varactor has a potential advantages such as stronger nonlinearities or special symmetry, which make it attractive for submillimeter wave frequency multiplication. The performance of a tripler using a SBV over a output frequency range from 186 to 207 GHz has been measured in a crossed waveguide mount. The theoretical performance of the device has been calculated using large signal analysis. A comparison of theoretical and measured results and a discussion of various losses in the mount and the varactor have also been presented.

Choudhury, Debabani↗
NASA NTRS1992

Source conductance scaling for high frequency superconducting quasiparticle receivers

It has been suggested that the optimum source conductance G(sub s) for the superconductor-insulator-superconductor (SIS) quasiparticle mixer should have a l/f dependence. This would imply that the critical current density of SIS junctions used for mixing should increase as frequency squared, a stringent constraint on the design of submillimeter SIS mixers, rather than in simple proportion to frequency as previously believed. We have used Tucker's quantum theory of mixing for extensive numerical calculations to determine G(sub s) for an optimized SIS receiver. We find that G(sub s) is very roughly independent of frequency (except for the best junctions at low frequency), and discuss the implications of our results for the design of submillimeter SIS mixers.

Ke, Qing↗
NASA NTRS1993

A 200 GHz tripler using a single barrier varactor

The GaAs Schottky varactor diode is the nonlinear device most commonly used for submillimeter wave harmonic generation. Output power adequate to serve as a local oscillator source for SIS tunnel junctions has been demonstrated with whisker-contacted GaAs Schottky varactor multipliers in waveguide mounts up to about 800 GHz. In this paper, we present results for a tripler to 200 GHz using a new multiplier device, the single barrier varactor (SBV). This new varactor has potential advantages such as stronger nonlinearities or special symmetry, which make it attractive for submillimeter wave frequency multiplication. The performance of a tripler using a SBV over a output frequency range from 186 to 207 GHz has been measured in a crossed waveguide mount. The theoretical performance of the device has been calculated using large signal analysis. A comparison of theoretical and measured results and a discussion of various losses in the mount and the varactor have also been presented.

Choudhury, Debabani↗
NASA NTRS1992

An IDL-based analysis package for COBE and other skycube-formatted astronomical data

UIMAGE is a data analysis package written in IDL for the Cosmic Background Explorer (COBE) project. COBE has extraordinarily stringent accuracy requirements: 1 percent mid-infrared absolute photometry, 0.01 percent submillimeter absolute spectrometry, and 0.0001 percent submillimeter relative photometry. Thus, many of the transformations and image enhancements common to analysis of large data sets must be done with special care. UIMAGE is unusual in this sense in that it performs as many of its operations as possible on the data in its native format and projection, which in the case of COBE is the quadrilateralized sphereical cube ('skycube'). That is, after reprojecting the data, e.g., onto an Aitoff map, the user who performs an operation such as taking a crosscut or extracting data from a pixel is transparently acting upon the skycube data from which the projection was made, thereby preserving the accuracy of the result. Current plans call for formatting external data bases such as CO maps into the skycube format with a high-accuracy transformation, thereby allowing Guest Investigators to use UIMAGE for direct comparison of the COBE maps with those at other wavelengths from other instruments. It is completely menu-driven so that its use requires no knowledge of IDL. Its functionality includes I/O from the COBE archives, FITS files, and IDL save sets as well as standard analysis operations such as smoothing, reprojection, zooming, statistics of areas, spectral analysis, etc. One of UIMAGE's more advanced and attractive features is its terminal independence. Most of the operations (e.g., menu-item selection or pixel selection) that are driven by the mouse on an X-windows terminal are also available using arrow keys and keyboard entry (e.g., pixel coordinates) on VT200 and Tektronix-class terminals. Even limited grey scales of images are available this way. Obviously, image processing is very limited on this type of terminal, but it is nonetheless surprising how much analysis can be done on that medium. Such flexibility has the virtue of expanding the user community to those who must work remotely on non-image terminals, e.g., via modem.

Ewing, J. A.↗
NASA NTRS1994

Circumprotostellar environments. 2: Envelopes, activity, and evolution

We have obtained 800 and 1100 micron photometric observations of a complete, flux-limited, IRAS-selected sample of cold sources in Taurus, whose infrared and molecular properties indicate them to be low-mass protostars which are younger than T Tauri stars. The goal of this study is to understand the role of the circumstellar envelope and disk during low-mass star formation and to search for signs of evolution. We find a good correlation between the submillimeter flux density (as well as of envelope mass) with both the mechanical luminosity of the molecular outflow and with the far-infrared luminosity, presumably produced by accretion onto the protostar. This suggests that the mass of the disk/envelope may be linked to the rate of accretion onto the protostar and to the generation of outflows. However, in contrast to the results of Cabrit & Andre (1991) we see no evidence for a lower limit to the disk/envelope mass which can produce outflow. We also find a significant difference between the spectral energy distributions at submillimeter wavelengths of embedded protostars compared to optically visible T Tauri stars. The more evolved (T Tuari) objects tend to have shallower spectral indices than embedded sources, suggesting (1) an evolution of dust grains, and/or (2) a more compact envelope and optically thick disk in the older objects.

Moriarty-Schieven, G. H.↗
NASA NTRS1995

A molecular line study of NGC 1333/IRAS 4

Molecular line surveys and fully sampled spectral line maps at 1.3 and 0.87 mm are used to examine the physical and chemical characteristics of the extreme Class I sources IRAS 4A and 4B in the L1450/NGC 1333 molecular cloud complex. A very well collimated, jetlike molecular flow emanates from IRAS 4A, with a dynamical age of a few thousand years. Symmetric, clumpy structure along the outflow lobes suggests that there is considerable variability in the mass-loss rate or wind velocity even at this young age. Molecular emission lines toward IRAS 4A and 4B are observed to be weak in the velocity range corresponding to quiescent material surrounding the young stellar objects (YSOs). Depletion factors of 10-20 are observed for all molecules, including CO, even for very conservative mass estimates from the measured millimeter and submillimeter dust continuum. However, abundance scaled with respect to CO are similar to other dark molecular cloud cores. Such depletions could be mimicked by high dust and optical depths or increased grain emissivities at the observing frequencies of 230 and 435 GHz, but the millimeter and submillimeter spectral energy distributions suggest that this is unlikely over the single-dish size scales of 5000-10,000 AU. Dense, outflowing gas is found to be kinematically, but not spatially, distinct from the quiescent material on these size scales. If CO is used as a chemical standard for the high-velocity gas, we find substantial enhancements in abundances of several molecules in outflowing material, most notably CS, SIO, and CH3OH. The SiO emission is kinematically well displaced from the bulk cloud velocity and likely arises from directly shocked material. As is the case for CO, however, the outflow features from more volatile species are centered near the cloud velocity and are often characterized by quite low rotational temperatures. We suggest that grain-grain collisions induced by velocity shear zones surrounding the outflow axes transiently desorb the grain mantles, resulting in large abundance enhancements of selected species. Similar results have recently been obtained in several other low-mass YSOs, where outflowing gas is often both kinematically and spatailly distinct, and are illustrative of the ability of accretion and outflow processes to simultaneously modify the composition of the gas and dust surrounding young stars.

Blake, Geoffrey A.↗