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.

SourceResearch connectionFrom yearThrough year

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

At least 415 records · Page 23

All sources NASA NTRS DOE OSTI

NASA NTRS1990

Image reconstruction of IRAS survey scans

The IRAS survey data can be used successfully to produce images of extended objects. The major difficulties, viz. non-uniform sampling, different response functions for each detector, and varying signal-to-noise levels for each detector for each scan, were resolved. The results of three different image construction techniques are compared: co-addition, constrained least squares, and maximum entropy. The maximum entropy result is superior. An image of the galaxy M51 with an average spatial resolution of 45 arc seconds is presented, using 60 micron survey data. This exceeds the telescope diffraction limit of 1 minute of arc, at this wavelength. Data fusion is a proposed method for combining data from different instruments, with different spacial resolutions, at different wavelengths. Data estimates of the physical parameters, temperature, density and composition, can be made from the data without prior image (re-)construction. An increase in the accuracy of these parameters is expected as the result of this more systematic approach.

Bontekoe, Tj. Romke↗

NASA NTRS1990

Image construction from the IRAS survey and data fusion

The IRAS survey data can be used successfully to produce images of extended objects. The major difficulty, viz. non-uniform sampling, different response functions for each detector, and varying signal-to-noise levels for each detector for each scan, were resolved. The results of three different image construction techniques are compared: co-addition, constrained least squares, and maximum entropy. The maximum entropy result is superior. An image of the galaxy M51 with an average spatial resolution of 45 arc seconds, is presented using 60 micron survey data. This exceeds the telescope diffraction limit of 1 minute of arc, at this wavelength. Data fusion is a proposed method for combining data from different instruments, with different spatial resolutions, at different wavelengths. Direct estimates of the physical parameters, temperature, density and composition, can be made from the data without prior images (re-)construction. An increase in the accuracy of these parameters is expected as the result of this more systematic approach.

Bontekoe, Tj. R.↗

NASA NTRS1990

Advanced technology optical telescopes IV; Proceedings of the Meeting, Tucson, AZ, Feb. 12-16, 1990. Parts 1 & 2

The present conference on the current status of large, advanced-technology optical telescope development and construction projects discusses topics on such factors as their novel optical system designs, the use of phased arrays, seeing and site performance factors, mirror fabrication and testing, pointing and tracking techniques, mirror thermal control, structural design strategies, mirror supports and coatings, and the control of segmented mirrors. Attention is given to the proposed implementation of the VLT Interferometer, the first diffraction-limited astronomical images with adaptive optics, a fiber-optic telescope using a large cross-section image-transmitting bundle, the design of wide-field arrays, Hartmann test data reductions, liquid mirrors, inertial drives for telescope pointing, temperature control of large honeycomb mirrors, evaporative coatings for very large telescope mirrors, and the W. M. Keck telescope's primary mirror active control system software.

Barr, Lawrence D.↗

NASA NTRS1991

Aberration corrected aspheric grating for far ultraviolet spectrographs - Conventional approach

Two approaches to reducing optical aberrations of concave grating spectrographs have been used, holographically controlling the groove curvature and spacing and reshaping the optical substrate while ruling the grooves conventionally. The latter approach, slightly deforming an ellipsoidal grating blank, can lead to diffraction-limited performance at a single FUV wavelength. When such a grating is used in a slitted Rowland circle spectrograph, the result is an extremely efficient spectrograph with spectral resolving power of about 30,000 and low astigmatism. Optical fabrication technology has advanced to the point where these exotic surface gratings are becoming practical.

Content, David↗

NASA NTRS1991

Low-threshold, CW, all-solid-state Ti:Al2O3 laser

A CW Ti:Al2O3 ring laser with a threshold power of 119 mW is demonstrated. It provides a tunable source of single-frequency, diffraction-limited radiation that is suitable for injection seeding. The Ti:Al2O3 laser is operated with a diode-laser-pumped, frequency-doubled, Nd:YAG laser as the sole pump source.

Harrison, James↗

NASA NTRS1991

High-power and high-spatial-coherence broad-area power amplifier

A broad-area AlGaAs amplifier operating CW has delivered 425 mW of total power with 342 mW in a single lobe diverging at 1.02 times the diffraction limit (FWHM 0.483 deg, 87.4-micron actual aperture) for a master oscillator input power of 70 mW. The spatial coherence of the amplifier output is 0.97, and the mutual spatial coherence between the oscillator and the amplifier is 0.96.

Andrews, John R.↗

NASA NTRS1991

Image construction from the IRAS survey

IRAS survey data can be used successfully to produce images of extended objects. The major difficulties, i.e., nonuniform sampling, different response functions for each detector, and varying signal-to-noise levels for each detector for each scan, have been resolved. The results of three different image construction techniques are compared: coaddition, constrained least-squares, and maximum entropy. The maximum entropy result is superior. An image of the galaxy M51 with an average spatial resolution of 45 arcsecods, using 60 microns survey data is presented. This exceeds the telescope diffraction limit of about 1 minute of arc at this wavelength.

Bontekoe, T. R.↗

NASA NTRS1990

An early lunar-based telescope - The Lunar Transit Telescope (LTT)

The first telescope accompanying return to the moon, a simple but elegant two meter class instrument capable of producing an extraordinary survey of the universe is proposed. This telescope produces a deep image of the sky obtained simultaneously in several broad bandpasses in the wavelength range from about 0.1 to 2 microns, with diffraction limited imaging in the infrared and approximately 0.1 arcsec resolution at shorter wavelengths. In an 18.6 year mission, the survey would include approximately 2 percent of the sky with multiple observations of all the surveyed area. This survey is accomplished with a telescope which has no moving parts and requires no continuing support beyond initial deployment.

Mcgraw, John T.↗

NASA NTRS1992

Transmission Of Power Via Combined Laser Beams

Laser Diode Array (LDA) appears to be most efficient means of transferring power from Earth to satellites and between satellites, in terms of mass and size, of various laser configurations. To form large-scale-array amplifier (LSAA), element LDA's must generate well-defined diffraction-limited beams. Coherent matching of phases among LDA's enables system to generate good beam pattern in far field over thousands of kilometers. By passing beam from master laser through number of LDA amplifiers simultaneously, one realizes coherence among amplified output beams. LSAA used for transmission of power with efficiency of approximately 80 percent into receiver of moderate size at 5,000 km. Also transmits data at high rates by line-of-sight rather than fiber optics.

Kwon, Jin H.↗

NASA NTRS1992

A solar magnetic and velocity field measurement system for Spacelab 2: The Solar Optical Universal Polarimeter (SOUP)

The Solar Optical Universal Polarimeter (SOUP) flew on the shuttle mission Spacelab 2 (STS-51F) in August, 1985, and collected historic solar observations. SOUP is the only solar telescope on either a spacecraft or balloon which has delivered long sequences of diffraction-limited images. These movies led to several discoveries about the solar atmosphere which were published in the scientific journals. After Spacelab 2, reflights were planned on the shuttle Sunlab mission, which was cancelled after the Challenger disaster, and on a balloon flights, which were also cancelled for funding reasons. In the meantime, the instrument was used in a productive program of ground-based observing, which collected excellent scientific data and served as instrument tests. Given here is an overview of the history of the SOUP program, the scientific discoveries, and the instrument design and performance.

Tarbell, Theodore D.↗

NASA NTRS1992

Near-infrared CCD observations of umbral dots

Umbral fine structure have been observed at 8500 A using a new CCD detector. Four frames with diffraction-limited seeing were obtained. Between 68 and 91 umbral dots with a brightness contrast greater than 2 percent were found in each frame, although no dots were found in the darkest part of the umbra. The intrinsic flux of the umbral dots varies widely, indicating that their intrinsic brightness does as well. The mean dot lifetime is estimated as 15 min, although some dots were observed to live more than 2 h. Some of the umbral dots are flowing into the umbra at speeds up to 0.5 km/s. These dots have higher than average contrast and are associated with penumbral grains.

Ewell, Malcolm W., Jr.↗

NASA NTRS1992

A 5-18 micron array camera for high-background astronomical imaging

A new infrared array camera system using a Hughes/SBRC 58 x 62 pixel hybrid Si:Ga array detector has been successfully applied to high-background 5-18-micron astronomical imaging observations. The off-axis reflective optical system minimizes thermal background loading and produces diffraction-limited images with negligible spatial distortion. The noise equivalent flux density (NEFD) of the camera at 10 microns on the 3.0-m NASA/Infrared Telescope Facility with broadband interference filters and 0.26 arcsec pixel is NEFD = 0.01 Jy/sq rt min per pixel (1sigma), and it operates at a frame rate of 30 Hz with no compromise in observational efficiency. The electronic and optical design of the camera, its photometric characteristics, examples of observational results, and techniques for successful array imaging in a high- background astronomical application are discussed.

Gezari, Daniel Y.↗

NASA NTRS1991

The 4-meter lunar engineering telescope

The 16-meter diffraction limited lunar telescope incorporates a primary mirror with 312 one-meter segments; 3 nanometer active optics surface control with laser metrology and hexapod positioners; a space frame structure with one-millimeter stability; and a hexapod mount for pointing. The design data needed to limit risk in this development can be obtained by building a smaller engineering telescope on the moon with all of the features of the 16-meter design. This paper presents a 4.33-meter engineering telescope concept developed by the Summer 1990 Student Program of the NASA/JHU Space Grant Consortium Lunar Telescope Project. The primary mirror, made up of 18 one-meter hexagonal segments, is sized to provide interesting science as well as engineering data. The optics are configured as a Ritchey-Chretien with a coude relay to the focal plane beneath the surface. The optical path is continuously monitored with 3-nanometer precision interferometrically. An active optics processor and piezoelectric actuators operate to maintain the end-to-end optical configuration established by wave front sensing using a guide star. The mirror segments, consisting of a one-centimeter thick faceplate on 30-cm deep ribs, maintain the surface figure to a few nanometers under lunar gravity and thermal environment.

Peacock, Keith↗

NASA NTRS1989

Catadioptric optics for laser Doppler velocimeter applications

This paper examines the adaptation of low-cost Schmidt-Cassegrain astronomical telescopes to perform the laser-beam-focusing and scattered-light collection tasks associated with dual-beam laser Doppler velocimetry. A generic telescope design is analyzed using ray-tracing methods and Gaussian beam-propagation theory. A straightforward modification procedure to convert from infinite to near unity conjugate-ratio operation with very low residual aberration is identified and tested with a 200-mm-aperture telescope modified for f/10 operation. Performance data for this modified telescope configuration are near the diffraction limit and agree well with predictions.

Dunagan, Stephen E.↗

NASA NTRS1992

SIRTF - Capabilities for planetary science

Major research areas of the Space Infrared Telescope Facility (SIRTF) are discussed which include Kuiper-belt comets, IR spectroscopy of comets, and circumstellar planetary debris disks. SIRTF instrumentation will include the infrared array camera (IRAC) and multiband imaging photometer (MIP). The IRAC uses large area, 2D infrared array detectors to provide wide-field (7 arcmin) and diffraction-limited imaging over the spectral region from 2 to 30 microns. The MIP will provide background-limited imaging and photometry over the wavelength range from 30 to 200 microns, wide-field, high resolution imaging from 50 to 120 microns, and broad band photometry and mapping from 200 to 700 microns.

Cruikshank, D. P.↗

NASA NTRS1992

High-efficiency, high-output-power antiguide laser diode arrays

Antiguide laser arrays have been fabricated and operated up to peak pulsed powers of 7.7 W in a beam with a full-width at half-maximum in the main lobe of 0.7 deg. Up to 0.7 W of continuous wave power is emitted into a radiation pattern 2.5 times the diffraction limit. By varying the temperature of the array to vary the operating wavelength of the device, the threshold gain condition of the array modes is altered, allowing thermal tuning of the far field of the device.

Mehuys, D.↗

NASA NTRS1992

Radio and optical interferometric imaging

Since diffraction-limited imaging with a single aperture yields angular resolution approx. lambda/D, the attainment of high angular resolution with single apertures requires the construction of correspondingly large monolithic apertures, the whole surface of which must be figured to much less than a wavelength. At the longer wavelengths, it is impossible to build a sufficiently large single aperture: for example, at lambda 21 cm, arcsec resolution requires an aperture of diameter approx. 50 km. At the shorter wavelengths, the atmosphere imposes a natural limit in resolution of about one arcsec. However, another route is possible; that is, using synthetic apertures to image the sky. Synthetic apertures are now in use in many fields, e.g., radio interferometry, radar imaging, and magnetic-resonance imaging. Radio-interferometric techniques developed in radio astronomy over the past 40 years are now being applied to optical and IR astronomical imaging by a number of groups. Furthermore, the problem of figuring synthetic apertures is considerably simpler, and can be implemented in a computer: new 'self-calibration' techniques allow imaging even in the presence of phase errors due to the atmosphere.

Cornwell, Tim J.↗

NASA NTRS1992

Modeling and measurement of a micro-optic beam deflector

The use is studied of a unity-magnification micro-optic beam deflector. The defelector consists of two arrays of positively powered lenslets. The lenslets on each array are arranged in a square grid. Design criteria are based on usefulness in optical data storage devices. The deflector is designed to operate over a + or - 1.6 range of deflection angles. Modeling results are compared with interferometric analysis of the wavefront from a single lenslet pair. The results indicate that the device is nearly diffraction limited, but there are substantial wavefront errors at the edges and corners of the lenslets.

Milster, Tom D.↗