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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 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Venus imaged with the Hat Creek interferometer in the J = 1-0 CO line

Venus 2.7-mm continuum emission and CO J = 1-0 transition observations conducted in January 1987, when Venus was at western elongation, indicate a 10 percent brightness temperature increase from the day to the nightside. It is suggested that this brightness temperature variation, which is greater than anticipated on the basis of physical variations in temperature, may be associated with potentially cloud-related atmospheric opacity variations. Model fits to the CO spectra suggest that, while the CO at altitudes greater than 90 km decreases from night to day, low altitude CO may exhibit a general enhancement.

De Pater, Imke↗
NASA NTRS1992

Equal path, phase shifting, sample point interferometer for monitoring the configuration of surfaces

A system for monitoring the configuration of a surface (e.g., a segmented parabolic surface) using orthogonally placed retroreflectors at sets of points 1, 2, and 3 dispersed throughout the surface with a stationary halfwave plate (HWP) in the front of the one retroreflector at a corner point 3 and a rotating halfwave plate (RHWP) over a source of linearly polarized coherent light, thereby causing the direction of linear polarization to continuously rotate through 360 deg and causing light returned by the retroreflector at point 3 to be continuously phase shifted through 360 deg relative to light returned by retroreflectors at points 1 and 2. The returned light from each set of points 1, 2, and 3 is focused onto a bed-of-nails (BON) phase grating diagonally oriented with respect to the orthogonal orientation of the incident beams from retroreflectors 1, 2, and 3, thereby causing overlap in the light from points 1 and 3 to produce interferometric signals 1,3 and 2,3. Any change in phase of the interferometric signals 1,3 and 2,3 indicates both the magnitude and direction of any change in the position of the retroreflector at point 3 relative to retroreflectors at points 1 and 2.

Manhart, Paul K.↗
NASA NTRS1992

Multimode fiber-optic broad spectral band interferometer

An interferometric technique for observing white light fringes on a mode-by-mode basis in long lengths of few-mode fiber is described. Each mode can be used as a separate channel with negligible cross talk from other modes because of the highly localized nature of interference. The spatial-mode separation technique makes it possible to observe the interference fringes without loss of visibility caused by multimode overlap effects. The high-contrast, broadband fringes observed in the multimode interference experiments indicate that a multimode fiber is capable of maintaining the coherence of injected light well beyond the point where intermodal path differences exceed the temporal coherence length.

Shaklan, S.↗
NASA NTRS1992

Sapphire-fiber-based intrinsic Fabry-Perot interferometer

A sapphire optical fiber intrinsic Fabry-Perot interferometric sensor is demonstrated. A length of multimode sapphire fiber that functions as a Fabry-Perot cavity is spliced to a silica single-mode fiber. The interferometric signals of this sensor are produced by the interference between the reflection from the silica-sapphire fiber splice and the reflection from the free end face of the sapphire fiber. This sensor has been demonstrated for temperature measurement. A resolution of 0.2 C has been obtained over a measurement range of 310 C to 976 C.

Wang, Anbo↗
NASA NTRS1993

The JPL Phase B interferometer testbed

Future NASA missions with large optical systems will require alignment stability at the nanometer level. However, design studies indicate that vibration resulting from on-board disturbances can cause jitter at levels three to four orders of magnitude greater than this. Feasibility studies have shown that a combination of three distinct control layers will be required for these missions, including disturbance isolation, active and passive structural vibration suppression, and active optical pathlength compensation. The CSI technology challenge is to develop these design and control approaches that can reduce vibrations in the optical train by a factor of 1000 to 10,000. The focus of the paper is on describing the Phase B Testbed structure and facility, as the experimental results are included in other papers presented at this same conference.

Eldred, Daniel B.↗
NASA NTRS1993

Optical pathlength control on the JPL Phase B interferometer testbed

Design and implementation of a controller for optical pathlength compensation on a flexible structure is presented. Nanometer level pathlength control is demonstrated in the laboratory. The experimental results are in close agreement with performance predictions.

Spanos, John T.↗
NASA NTRS1992

Very long baseline interferometer measurements of plasma turbulence in the solar wind

Plasma turbulence in the solar wind is investigated using angular broadening VLBI measurements at 4.99 GHz of ten extragalactic compact radio sources (quasars). The measured broadening size was corrected for intrinsic source structures which were obtained from separate VLBI observations. It was found that the measured angular sizes are considerably less than those predicted by the Erickson's (1964) empirical relationship, as well as by two other models for the strength of scattering as a function of solar elongation. However, the measurements are in good agreement with a model for the spatial power spectrum of turbulence, proposed by Coles and Harmon (1989).

Sakurai, Takayuki↗
NASA NTRS1992

Sapphire fiber interferometer for microdisplacement measurements at high temperature

Attention is given to the use of a short-length multimode sapphire rod as an extension to a conventional Michelson interferometric configuration, but with operation of Fabry-Perot cavity-based sensor element type. The performance of such a device as an interferometric sensor is demonstrated for a case where the interference between the reflections from the sapphire-air interface and an air-metallic surface is inspected for microdisplacements of the metallic surface. A detailed account is given of the sensor's fabrication procedure; results are presented for the detection of surface-acoustic waves.

Murphy, Kent A.↗
NASA NTRS1991

Sapphire fiber interferometer for microdisplacement measurements at high temperatures

We report the use of a short-length, multimode sapphire rod as an extension to a Michelson configuration, but operated as a low-finesse Fabry-Perot cavity. We demonstrate the performance of such a device as an interferometric sensor, where the interference between the reflections from the sapphire-air interface and an air-metallic surface is observed for microdisplacement of the metallic surface which is placed close to the sapphire endface. We describe in detail the fabrication procedure and present results obtained from the detection of temperature changes, applied strain, and surface acoustic waves.

Murphy, Kent A.↗
NASA NTRS1992

Airglow studies using an all-reflection interferometer for extreme ultraviolet spectroscopy (ARIES)

Ultrahigh resolution line studies can deepen insight into the excitation processes and structures of the upper atmosphere; attention is presently given to the possibility of a study of terrestrial atomic oxygen in the thermosphere through measurements of the O I 1304 A solar and terrestrial airglow emissions from a sounding rocket. These line profile studies of the airglow yield a relative contribution of the two main excitation mechanisms (photoelectron impact and solar-resonance scattering), as well as a verification of cross section and branching ratios.

Cotton, D. M.↗
NASA NTRS1993

Dynamic interferometer alignment and its utility in UV Fourier transform spectrometer systems

Dynamic alignment has been demonstrated as a practical approach to alignment maintenance for systems in the infrared region of the spectrum. On the basis of work done by OPTRA, this technique was introduced in commercial Fourier transform spectrometer systems in 1982 and in various forms is now available from a number of manufacturers. This paper reports on work by OPTRA to extend the basic technique to systems operating in the ultraviolet. In addition, this paper reports the preliminary results of the development of an alignment system using a laser diode in place of a gas laser normally found in dynamic alignment systems. A unique optical system and spatial heterodyne technique allows for achievement of a metrology system with characteristics that fully satisfy the requirements of an ultraviolet spectrometer system.

Dorval, Rick K.↗
NASA NTRS1993

Hubble Space Telescope COSTAR asphere verification with a modified computer-generated hologram interferometer

To correct for the spherical aberration in the Hubble Space Telescope primary mirror, five anamorphic aspheric mirrors representing correction for three scientific instruments have been fabricated as part of the development of the corrective-optics space telescope axial-replacement instrument (COSTAR). During the acceptance tests of these mirrors at the vendor, a quick and simple method for verifying the asphere surface figure was developed. The technique has been used on three of the aspheres relating to the three instrument prescriptions. Results indicate that the three aspheres are correct to the limited accuracy expected of this test.

Feinberg, L.↗
NASA NTRS1991

Optical pathlength control in the nanometer regime on the JPL phase B interferometer testbed

This paper describes experimental research being performed at the Jet Propulsion Laboratory to develop and validate control concepts arising out of NASA's Control Structure Interaction program. The facility is meant to be a ground testbed with relevance to a broad class of future precision optical space systems. The objective of the experimental program is to investigate a multi-layer control approach to the maintenance of nanometer level optical pathlength control in the presence of external disturbances and multiple structural resonances. A brief overview of the experimental facility is presented. The control design methodology is discussed, and several experimental results are presented.

O'Neal, Michael C.↗