Search NASA⌕ Search

SEARCH · Search NASA

Results for “Diffraction limited”

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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Restoration of multichannel microwave radiometric images

A constrained iterative image restoration method is applied to multichannel diffraction-limited imagery. This method is based on the Gerchberg-Papoulis algorithm utilizing incomplete information and partial constraints. The procedure is described using the orthogonal projection operators which project onto two prescribed subspaces iteratively. Its properties and limitations are presented. The effect of noise was investigated and a better understanding of the performance of the algorithm with noisy data has been achieved. The restoration scheme with the selection of appropriate constraints was applied to a practical problem. The 6.6, 10.7, 18, and 21 GHz satellite images obtained by the scanning multichannel microwave radiometer (SMMR), each having different spatial resolution, were restored to a common, high resolution (that of the 37 GHz channels) to demonstrate the effectiveness of the method. Both simulated data and real data were used in this study. The restored multichannel images may be utilized to retrieve rainfall distributions.

Chin, R. T.↗
NASA NTRS1985

A 94 GHz imaging array using slot line radiators

A planar endfire slotted-line antenna structure was investigated. It was found that the H-plane beamwidths are basically dependent upon the substrate properties, whereas the E-plane beamwidths are more strongly a function of the slot's shape and size. It is shown that these antennas produce symmetrical E and H-plane beamwidths while following Zucker's standard traveling-wave antenna beamwidth curves over some range of antenna normalized length. An empircally derived design formula for effective substrate thickness is shown to predict this range for linearly tapered slotted-line antennas. The experimental imaging properties of these arrays are presented and imaging theory is discussed. It is shown that a minimum spacing of elements is necessary for exact reconstruction for a sampled image in a diffraction limited system. Because these LTSA elements employ the traveling-wave mechanism of radiation, they can be spaced two times closer than a conical feed horn of comparable beamwidth.

Korzeniowski, T. L.↗
NASA NTRS1985

The infrared size of IRc2/KL and its structure on an arcsecond scale

Small-aperture diffraction-limited scans of IRc2/KL at 7.8 and 12.5 microns are discussed. These scans, which were made at several position angles, spatially resolve the region within a 250 AU radius of this source, which is thought to be a newly formed luminous star undergoing heavy mass loss. IRc2 is found to have a pronounced elongation. The shape and orientation of this extended structure is similar to that seen on a larger scale in low-excitation molecular transitions, and is very similar to the distribution of H2O 'shell' masers. The size of the object may be reconciled with its dereddened blackbody temperature and total luminosity of 0.00001 solar luminosities (which is appropriate to OMC1) by the presence of small-scale structure. The observations thus support the idea that IRc2 is the primary luminosity source for OMC1. New astrometric measurements indicate that the 12.5 microns peak of IRc2 is coincident with the positions of the two bright SiO masers to within 0.3 arcsec.

Lester, D. F.↗
NASA NTRS1985

Impact of chopping on image quality in the SIRTF telescope

The initial Phase-A concept for the Space Infrared Telescope Facility (SIRTF), which was established in 1981, is concerned with a cryogenically cooled, 85 cm diameter, f/24 Ritchey-Chretien telescope, followed by a Multiple Instrument Chamber (MIC), containing six scientific instruments. In 1982, the Phase-A concept was reviewed with the aim to assess the technical readiness for the next phase of development. Various areas of concern were subsequently investigated in three parallel studies by industry. Two of the arising questions are considered in the present paper, taking into account the system and technology implications of achieving diffraction-limited resolution at 2 microns, and the limitations on the size of the imaging field under this condition. The conducted study takes into account an evaluation of the different methods of chopping. Attention is given to the telescope parameters, symmetric chopping, asymmetrical chopping, focus and alignment errors, the wavefront-error budget, and image quality.

Bottema, M.↗
NASA NTRS1986

High-efficiency broad-area single-quantum-well lasers with narrow single-lobed far-field patterns prepared by molecular beam epitaxy

Broad-area single-quantum-well graded-index waveguide separate-confinement heterostructure lasers were fabricated by molecular beam epitaxy. A high external quantum efficiency of 79 percent and stable, single-lobed far-field patterns with a beam divergence as narrow as 0.8 deg (1.9 times diffraction limit) for a 100 micron-wide laser were obtained under pulsed conditions.

Larsson, A.↗
NASA NTRS1986

Far-infrared structure in the nuclear region of M51

Far-infrared (100-micron) scans across the nucleus of M51 are presented. These scans show that much of the far-infrared luminosity of this galaxy comes from a small, sharply bounded region within a 30 arcsec radius (700 pc) of the nucleus. This radius corresponds to the innermost spiral structure, as well as that estimated from dynamical models for the radius of the inner Lindblad resonance. The results of a nonlinear image restoration analysis of the data are presented. This analysis, carried out with two different algorithms, yields information on the spatial structure of star formation near the nucleus that exceeds the diffraction limit of the telescope at this wavelength. This 'superresolution' treatment shows that star formation is enhanced at the outer edge of this region compared to the nucleus, which appears to be relatively devoid of young stars. This ring of active star formation may be produced in the same way as that seen in our own Galaxy at a galactocentric radius of 4-5 kpc and may indicate that the region near the nucleus has been swept clean of material by violent processes.

Lester, D. F.↗
NASA NTRS1985

Optical performance of synthetic aperture telescope configurations

The diffraction-limited performances of synthetic aperture configuration arrays of four telescopes, used for coherent imaging or beam transmission, are calculated and compared. The optical performance of phased telescope arrays was found to be more sensitive to rms piston errors than to rms tilt errors. Image degradation due to pupil mapping errors imposes tight tolerances upon the structural integrity of the telescope. One part in 10,000 pupil mapping error limits the field-of-view to approximately 30 arcsec. Field curvature of the independent telescopes provides a fundamental limit to the field-of-view for phased arrays made up of two-mirror telescopes. These field-of-view limitations may profoundly affect target acquisition, tracking, or imaging applications.

Harvey, J. E.↗
NASA NTRS1986

The spatial structure of IRC + 10216 and NGC 7027 in the far-infrared

Spatial scans of IRC + 10216 and NGC 7027 were made at 50 and 100 microns using a diffraction-limited slit. Maximum entropy deconvolution techniques were applied to the data and, in effect, the structure of these sources was probed down to a scale far smaller than previously achieved at these wavelengths. IRC + 10216 was unresolved on a spatial scale of several arcsecs and a low upper limit to either the dust-gas ratio or the bulk emissivity of the grains was implied for the large molecular envelope surrounding the star. NGC 7027 was easily resolved in the scans, with far-infrared emission distribution corresponding closely with the distribution of ionized gas and shorter wavelength infrared emission.

Lester, D. F.↗
NASA NTRS1986

High resolution imaging

Diffraction-limited telescopic observations were obtained of solar system objects and a program of research into Uranus, Neptune, Pluto and the asteroids based upon the data obtained was persued. Two camera systems appropriate for this work were developed. Most importantly, the PAPA photon address camera was developed and proven. Algorithms were developed for both phase and amplitude recovery and were validated on theoretical and laboratory data and to a limited extent on telescopic data. A laboratory simulator was constructed that was used for development but is also available for controlled investigation of image reconstruction. During 1985 two successful expeditions were made to Hawaii and Cerro Tololo and a large body of data on Pluto, Uranus, Neptune and two asteroids are on tape.

Goody, R.↗
NASA NTRS1987

Passive isolation/damping system for the Hubble space telescope reaction wheels

NASA's Hubble Space Telescope contain large, diffraction limited optics with extraordinary resolution and performance for surpassing existing observatories. The need to reduce structural borne vibration and resultant optical jitter from critical Pointing Control System components, Reaction Wheels, prompted the feasibility investigation and eventual development of a passive isolation system. Alternative design concepts considered were required to meet a host of stringent specifications and pass rigid tests to be successfully verified and integrated into the already built flight vehicle. The final design employs multiple arrays of fluid damped springs that attenuate over a wide spectrum, while confining newly introduced resonances to benign regions of vehicle dynamic response. Overall jitter improvement of roughly a factor of 2 to 3 is attained with this system. The basis, evolution, and performance of the isolation system, specifically discussing design concepts considered, optimization studies, development lessons learned, innovative features, and analytical and ground test verified results are presented.

Hasha, Martin D.↗
NASA NTRS1985

Construction of a multilayered X-ray telescope for solar coronal studies from space

The construction and testing of soft x-ray Ritchey-Chretien aplanatic telescope which is to be flown on a NASA sounding rocket in 1986 for very high resolution studies of the solar corona are discussed. Goals include figuring, polishing and measuring the mirror surfaces to tolerances exceding the 5000 A wavelength diffraction limit while achieving a superpolished surface finish, and the development of a structural design to withstand the rigors of the launch. Multilayer coatings are used to achieve usable reflectivity in the soft X-ray regime, and the design goal is for spatial resolution of 1/4 sec. Future applications are discussed.

Golub, L.↗
NASA NTRS1986

Far-infrared image restoration analysis of the protostellar cluster in S140

Image restoration techniques are applied to one-dimensional scans at 50 and 100 microns of the protostellar cluster in S140. These measurements resolve the surrounding nebula clearly, and Fourier methods are used to match the effective beam profiles at these wavelengths. This allows the radial distribution of temperature and dust column density to be derived at a diffraction limited spatial resolution of 23 arcsec (0.1 pc). Evidence for heating of the S140 molecular cloud by a nearby ionization front is established, and the dissociation of molecules inside the ionization front is spatially well correlated with the heating of the dust. The far-infrared spectral distribution of the three near-infrared sources within 10 arcsesc of the cluster center is presented.

Lester, D. F.↗
NASA NTRS1986

Optical efficiency of far-infrared photoconductors

The present optimization of the geometry of far-IR photoconductive detectors with diffraction-limited throughput, on the basis of experimental and theoretical results, gives attention to the internal optical path relative to measured absorption length, photoconductive gain, uniformity of illumination, cosmic ray cross section, and design compatibility with the requirements of one- and two-dimensional arrays. It is demonstrated that a rod-shaped, square cross section detector geometry, having lateral face electrodes and a beveled backface with which to trap the radiation by total internal reflection, exhibits responsivity commensurate with that of the best available detectors in integrating cavities.

Wang, J.-Q.↗
NASA NTRS1986

Cryogenic optical systems and instruments II; Proceedings of the Meeting, Los Angeles, CA, Jan. 23, 24, 1986

The topics of the present conference encompass cryogenic optical system design considerations, cryogenic instruments and their components, the design and performance of cryogenic dewars for space, and technologies supporting cryogenic systems and instruments. Attention is given to the Space IR Telescope Facility (SIRTF) observatory's design and on-orbit servicing, hardware development for the Gravity Probe-B program, the multiband imaging photometer aboard SIRTF, and the SIRTF wide field, diffraction-limited array camera. Also discussed are the cryogenic star-tracking telescope for Gravity Probe-B, a balloon-borne spectrometer for measurement of lower stratospheric trace constituents, the primary mirror support system design for a cryogenic space telescope, and the SQUID readout and ultralow magnetic fields of Gravity Probe-B.

Melugin, Ramsey K.↗
NASA NTRS1986

Grazing incidence optics; Proceedings of the Meeting, Orlando, FL, Apr. 3, 4, 1986

Papers are presented on the diffraction-limited performance of grazing incidence optical systems; transverse ray aberrations of Wolter type 1 telescopes; hybrid X-ray telescope systems; surface characterization of grazing incidence optics in the extreme UV and X-ray regions; and the surface roughness properties of synchrotron radiation optics. Topics discussed include the simulation of free-abrasive grinding of grazing incidence mirrors with vertical-honing and flexible blades; mirrors for the Extreme Ultraviolet Explorer; the design and development of conical X-ray imaging mirrors; thermal loading considerations for synchrotron radiation mirrors; and grazing incidence optics for synchrotron radiation insertion-device beams. Consideration is given to the interpretation of glancing incidence scattering measurements; damage processes in short wavelength coated FEL optics; the replication of grain incidence optics; and the assembly and alignment of the Technology Mirror Assembly.

Osantowski, John F.↗
NASA NTRS1986

White-light movies of the solar photosphere from the SOUP instrument on Spacelab

Initial results are presented on solar granulation, pores and sunspots from the white-light films obtained by the Solar Optical Universal Polarimeter (SOUP) instrument in Spacelab 2. Several hours of movies were taken at various disk and limb positions in quiet and active regions. The images are diffraction-limited at 0.5 arcsec resolution and are, of course, free of atmospheric seeing and distortion. Properties of the granulation in magnetic and nonmagnetic regions are compared and are found to differ significantly in size, rate of intensity variation, and lifetime. In quiet sun, on the order of fifty-percent of the area has at least one 'exploding granule' occurring in it during a 25-min period. Local correlation tracking has detected several types of transverse flows, including systematic outflow from the penumbral boundary of a spot, motion of penumbral filaments, and cellular flow patterns of supergranular and mesogranular size. Feature tracking has shown that, in the quiet sun, the average granule fragment has a velocity of about one kilometer/second.

Title, A. M.↗
NASA NTRS1986

A parametric study of various synthetic aperture telescope configurations for coherent imaging applications

The comparative advantages of synthetic aperture telescopes (SATs) of segmented primary mirror and common secondary mirror type, on the one hand, and on the other those employing an array of independent telescopes, are discussed. The diffraction-limited optical performance of both redundant and nonredundant subaperture configurations are compared in terms of point spread function characteristics and encircled energy plots. Coherent imaging with afocal telescope SATs involves a pupil-mapping operation followed by a Fourier transform one. A quantitative analysis of the off-axis optical performance degradation due to pupil-mapping errors is presented, together with the field-dependent effects of residual design aberrations of independent telescopes.

Harvey, James E.↗
NASA NTRS1986

Loss factors associated with spatial and temporal tracking errors in intersatellite PPM communication links

The performance of an optical PPM intersatellite link in the presence of spatial and temporal tracking errors is investigated. It is shown that for a given rms spatial tracking error, an optimal transmitter beamwidth exists which minimizes the probability of bit error. The power penalty associated with the spatial tracking error when the transmitter beamwidth is adjusted to achieve optimal performance is shown to be large (greater than 9 dB) when the rms pointing jitter becomes a significant fraction (greater than 30 percent) of the diffraction limited beamwidth. The power penalty due to temporal tracking error, on the other hand, is relatively small (less than 0.1 dB) when the tracking loop bandwidth is less than 0.1 percent of the slot frequency. By properly allocating losses to spatial and temporal tracking errors, it is seen that a 10 to the -9th error rate can be achieved for a realistic link design with an approximately 3 dB signal power margin.

Chen, C. C.↗