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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Optical-precision alignment of diffraction grating mold in moire interferometry

A high-precision optical method is presented for aligning diffraction grating molds with the edges of specimens in moire interferometry. The alignment fixture is simple and convenient to operate. The conventional method of grating-mold alignment has a wide band of uncertainty in the range of error which is not compatible with the required precision of high-sensitivity moire interferometry. Following a description of the alignment technique, both the single-edge and parallel-edge guide bar optical alignment methods are introduced and compared.

Joh, D.↗
NASA NTRS1990

A semi-micromechanic interlaminar strain analysis on curved-beam specimens

Experimental analyses were performed for determination of interlaminar strains in circumferentially unidirectional curved beam specimens. Semi-circular and semi-elliptic carbon-epoxy specimens were subjected to opening mode tensile loadings. Whole field measurements were recorded at load levels from about 5 to more than 90 pct of failure loads. Contour maps of displacement fields were obtained by using moire interferometry, using reference gratings of 2400 lines/mm or 60,690 lines/in. Whole field contour maps of circumferential and interlaminar strains were obtained by using moire interferometry in a semi-micromechanic scale. Various anomalous effects were observed in the displacement fields. The zig-zag fringe patterns indicated that the fiber orientation in each layer was not truly circumferential. This deviation from the unidirectionality caused free-edge effects, such as interlaminar shear strains even at the axis of symmetry and the altered normal strains in the thickness direction. In the resin rich zones between layers, the tensile interlaminar strain was excessively large due to the large compliance. As the result of the combined effect of these anomalous behaviors, the values of the interlaminar tensile strains were larger than those predicted analytically. The modulus E sub 3 was actually smaller than the assumed value E sub 2 by 20 pct.

Joh, Duksung↗
NASA NTRS1984

Deformation measurements of composite multi-span beam shear specimens by Moire interferometry

Experimental analyses were performed for determination of in plane deformations and shear strains in unidirectional and quasi-isotropic graphite-epoxy beams. Forty-eight ply beams were subjected to 5 point and 3 point flexure. Whole field measurements were recorded at load levels from about 20% to more than 90% of failure loads. Contour maps of U and W displacement fields were obtained by moire interferometry, using reference gratings of 2400 lines/mm. Clearly defined fringes with fringe orders exceeding 1000 were obtained. Whole field contour maps of shear strains were obtained by a method developed for these tests. Various anomalous effects were detected in the displacement fields. Their analysis indicated excess shear strains in resin rich zones in regions of shear tractions; free edge shear strains in quasi-isotropic specimens in regions of normal stresses; and shear stresses associated with cyclic shear compliances of quasi-isotropic plies in regions of shear tractions. Their contributions could occur independently or in superposition. Qualitative analyses addressed questions of relaxation; influence of contact stress distribution; specimen failure; effect of specimen overhang; nonlinearity; and qualities of 5 and 3 point flexure tests.

Post, D.↗
NASA NTRS1985

Shear strain anomalies in composite beam specimens by moire interferometry

Experimental analyses were performed for determination of in-plane deformations and shear strains in unidirectional and quasi-isotropic graphite-epoxy beams. Forty-eight-ply beams were subjected to five-point and three-point flexure. Whole-field measurements were recorded at load levels from about 20 percent to more than 90 percent of failure loads. Contour maps of U and W displacement fields were obtained by moire interferometry, using reference gratings of 2400 lines/mm. Clearly defined fringes with fringe orders exceeding 1000 were obtained. Whole-field contour maps of shear strains were obtained. Various anomalous effects were detected in the displacement fields. Their analysis indicated excess shear strains in resin-rich zones in regions of shear tractions; free-edge shear strains in quasi-isotropic specimens in regions of normal stresses, and shear stresses associated with cyclic shear compliances of quasi-isotropic laminates in regions of shear tractions. Their contributions could occur independently or in superposition. Qualitative analyses addressed questions of the effect of specimen overhang, nonlinearity, and characteristics of five-point and three-point flexure tests.

Post, D.↗
NASA NTRS1988

Transmission X-ray diffraction grating alignment using a photoelastic modulator

A high-resolution alignment technique which utilizes the partial polarization property of fine period transmission gratings has been developed. It is especially useful when the grating period is sufficiently small so that there are no visible diffracted orders. This technique uses a photoelastic modulator (PEM) to produce an intensity signal that is proportional to the sine of twice the angle between the grating lines and the PEM crystal axis. The experimentally demonstrated resolution of this technique on 200-nm period gold transmission gratings is better than 1 arc sec. This technique was developed to align X-ray transmission gratings for spectroscopy and interferometry applications.

Anderson, Erik H.↗
NASA NTRS1986

Optics in engineering measurement; Proceedings of the Meeting, Cannes, France, December 3-6, 1985

The present conference on optical measurement systems considers topics in the fields of holographic interferometry, speckle techniques, moire fringe and grating methods, optical surface gaging, laser- and fiber-optics-based measurement systems, and optics for engineering data evaluation. Specific attention is given to holographic NDE for aerospace composites, holographic interferometry of rotating components, new developments in computer-aided holography, electronic speckle pattern interferometry, mass transfer measurements using projected fringes, nuclear reactor photogrammetric inspection, a laser Doppler vibrometer, and optoelectronic measurements of the yaw angle of projectiles.

Fagan, William F.↗
NASA NTRS1991

Variable sensitivity moire interferometry

This paper demonstrates that optical microlithography can be used to produce a crossed grating which diffracts light into multiple orders sufficient to record moire interferograms with sensitivities ranging from 2.0 to 0.285 micron/fringe. The grating profile produced by the method is analyzed to establish the diffraction efficiency in each diffraction order, and generalized expressions are given for variable sensitivity moire interferometry. Experimental tests are conducted to verify analytical arguments. In one of these tests, two different diffraction order pairs are used simultaneously to verify that surface displacement can be measured at different sensitivities.

Johnson-Cole, Helen↗
NASA NTRS1993

Laser beam collimation using Talbot interferometry

A modified method of checking laser beam collimation using a single grating and a right-angled prism is presented. The self-images (Talbot images) of a grating illuminated by a collimated beam are formed at some distance from the grating. The use of a right-angled prism makes it possible to carry out the folding of the self-image with respect to the original grating and to ensure that the grating lines in the self-image and the actual grating are inclined at equal angles with respect to horizontal direction. It is concluded that the proposed collimation test method has an in-built reference and does not require precise orientation of the grating as in the two-grating method. Large beams can be tested with a small-size assembly.

Ganesan, A. R.↗
NASA NTRS2000

All-Optical Micro Motors Based on Moving Gratings in Photosensitive Media

An all-optical micro motor with a rotor driven by a traveling wave of surface deformation of a stator being in contact with the rotor is being studied. Instead of an ultrasonic wave produced by an electrically driven piezoelectric actuator as in ultrasonic motors, the wave is a result of a photo induced surface deformation of a photosensitive material produced by a traveling holographic grating. Two phase modulated coherent optical beams generate the grating. Several types of photosensitive materials are studied such as photorefractive crystals, photosensitive piezoelectric ceramics, and side-chain liquid crystalline polyesters. In order to be considered as a possible candidate for micro motors, the material should exhibit surface deformation produced by moving grating of the order of 10 micron. Deformations produced by static holographic gratings are studied in photorefractive crystals of LiNbO3 using high vertical resolution surface profilometer Dektak 3 and surface interferometer WYKO. An experimental set-up with moving grating has been developed. The set-up uses a two-beam interferometry configuration with one beam being reflected by a thin mirror mounted on a loud speaker. A ramp voltage signal generator drives the speaker. Changing voltage, polarity, and frequency of the signal can easily generate vibrating gratings or moving gratings in both directions. A vibrating grating has been applied to a photorefractive crystal of BSO controlled by an external electric field of the order of 104 V/cm. We have additionally studied effects of moving grating interaction with light absorbing fluids such as solutions of 2,9,16,23-Tetrakis(phenylthio)-29H, 31 Hphthalocyanine in chlorobenzene in capillary tubes. The purpose of using a liquid is to show that the moving gratings can force a liquid to shift. The interaction of a single low power focused laser beam at 633 nm with such fluid produced an intensive circular motion, which also might be applied to all-optical micro motors or actuators.

Curley, M.↗
NASA NTRS1981

Moire interferometry for thermal expansion of composites

Moire interferometry by reflection has been demonstrated using a real reference grating of 1200 lines/mm. The method is shown to be well adapted to thermal environments. Thermal expansion coefficients of graphite-epoxy composites have been measured with high precision over a wide range from nearly zero to 3300 microstrains in the temperature range 297-422 K. Random errors characterized by one standard deviation can be as small as one microstrain.

Bowles, D. E.↗
NASA NTRS1982

Advances in Moire interferometry for thermal response of composites

An experimental technique for the precise measurement of the thermal response of both sides of a laminated composite coupon specimen uses Moire interferometry with fringe multiplication which yields a sensitivity of 833 nm (32.8 micro in.) per fringe. The reference gratings used are virtual gratings and are formed by partially mirrorized glass prisms in close proximity to the specimen. Results are compared with both results obtained from tests which used Moire interferometry on one side of composite laminates, and with those predicted by classical lamination theory. The technique is shown to be capable of producing the sensitivity and accuracy necessary to measure a wide range of thermal responses and to detect small side to side variations in the measured response. Tests were conducted on four laminate configurations of T300/5208 graphite epoxy over a temperature range of 297 K (75 F) to 422 K (300 F). The technique presented allows for the generation of reference gratings for temperature regimes well outside that used in these tests.

Brooks, E. W., Jr.↗
NASA NTRS1982

Moire interferometry for thermal expansion of composites

Moire interferometry by reflection is described and demonstrated for the case of a real reference grating of 1200 lines/mm. Extraneous beams can be displaced and stopped by using a wedge-shaped air gap between reference and specimen gratings. Double-order dominance, the use of diffraction sequences for reflection, the isolation of preferred sequences, and the use of two-beam interference are discussed. Experimental accuracy is enhanced significantly by using several data points to establish displacements along a line, and random errors characterized by one standard deviation can be as small as one microstrain. The method is well adapted to thermal environments, coefficients of thermal expansion of selected graphite-epoxy laminates being determined in the temperature range of 297-422 K. Very good precision was achieved for a wide range of thermal expansion coefficients, from approximately zero to 27 microstrains/K.

Bowles, D. E.↗
NASA NTRS2004

A Micromachined Geometric Moire Interferometric Floating-Element Shear Stress Sensor

This paper presents the development of a floating-element shear stress sensor that permits the direct measurement of skin friction based on geometric Moir interferometry. The sensor was fabricated using an aligned wafer-bond/thin-back process producing optical gratings on the backside of a floating element and on the top surface of the support wafer. Experimental characterization indicates a static sensitivity of 0.26 microns/Pa, a resonant frequency of 1.7 kHz, and a noise floor of 6.2 mPa/(square root)Hz.

Horowitz, S.↗
NASA NTRS2023

2023 Astrophotonics Roadmap: Pathways to Realizing Multi-Functional Integrated Astrophotonic Instruments

Photonic technologies offer numerous functionalities that can be used to realize astrophotonic instruments. The most spectacular example to date is the ESO Gravity instrument at the Very Large Telescope in Chile that combines the light-gathering power of four 8 m telescopes through a complex photonic interferometer. Fully integrated astrophotonic devices stand to offer critical advantages for instrument development, including extreme miniaturization when operating at the diffraction-limit, as well as integration, superior thermal and mechanical stabilization owing to the small footprint, and high replicability offering significant cost savings. Numerous astrophotonic technologies have been developed to address shortcomings of conventional instruments to date, including for example the development of photonic lanterns to convert from multimode inputs to single mode outputs, complex aperiodic fiber Bragg gratings to filter OH emission from the atmosphere, complex beam combiners to enable long baseline interferometry with for example, ESO Gravity, and laser frequency combs for high precision spectral calibration of spectrometers. Despite these successes, the facility implementation of photonic solutions in astronomical instrumentation is currently limited because of (1) low throughputs from coupling to fibers, coupling fibers to chips, propagation and bend losses, device losses, etc, (2) difficulties with scaling to large channel count devices needed for large bandwidths and high resolutions, and (3) efficient integration of photonics with detectors, to name a few. In this roadmap, we identify 24 key areas that need further development. We outline the challenges and advances needed across those areas covering design tools, simulation capabilities, fabrication processes, the need for entirely new components, integration and hybridization and the characterization of devices. To realize these advances the astrophotonics community will have to work cooperatively with industrial partners who have more advanced manufacturing capabilities. With the advances described herein, multi-functional integrated instruments will be realized leading to novel observing capabilities for both ground and space based platforms, enabling new scientific studies and discoveries.

astrophotonics↗
NASA NTRS2016

Khayyam; Progress and Prospects of Coupling a Spatial Heterodyne Spectrometer (SHS) to a Cassegrain Telescope for Optical Interferometry

In the temporal study of faint, extended sources at high resolving power, Spatial Heterodyne Spectrometer (SHS) can offer significant advantages about conventional dispersive grating spectrometers. We describe here a four-year continuous progress in Mt. Hamilton, Lick Observatory, toward development of a prototype reflective Spacial Heterodyne Spectrometer, Khayyam, instrument-telescope configuration to combine all of the capabilities necessary to obtain high resolving power visible band spectra of diffuse targets from small aperture on-axis telescopes where significant observing time can be obtained. We will discuss the design considerations going into this new system, installation, testing of the interferometer-telescope combination, the technical challenges and procedures moving forward.

extended targets↗
NASA NTRS2001

Analysis of Spacelab-III Reconstructed Wavefronts by Non-Holographic Methods

Holography has been used in several past space missions. One popular experimental mode deals with study of fluid refractive properties in the crystal growth cell. The perceived advantage of holography is that it stores and reconstructs wavefronts so that a complete information is available later on ground. That means the wavefront can be analyzed not only by traditional holographic interferometry but other means as well. We have successfully demonstrated two such means being described here. One is deflectometry using a Ronchi grating and the other confocal optical processing. These results, using holograms from Spacelab-III mission dealing with triglycine sulfate crystal growth clearly demonstrate that a single hardware (holography) can do the task of several fluid experimental systems. Finally, not experimentally demonstrated, the possibility of some other analysis modes like speckle techniques and video holography using the reconstructed wavefronts have been described. Since only traditional holographic interferometry has been used in the past leading to the argument that non-holographic interferometry hardware in space could do the job, the present study firmly establishes advantage of holography.

Vikram, Chandra S.↗
NASA NTRS1992

A comparative evaluation of in-plane shear test methods for laminated graphite-epoxy composites

The objectives were to evaluate popular shear test methods for various forms of graphite-epoxy composite materials and to determine the shear response of graphite-epoxy composites with various forms of fiber architecture. Numerical and full-field experimental stress analyses were performed on four shear test configurations for unidirectional and bidirectional graphite-epoxy laminates to assess the uniformity and purity of the shear stress (strain) fields produced in the specimen test section and to determine the material in-plane shear modulus and shear response. The test methods were the 10 deg off-axis, the +/- 45 deg tension, the Iosipescu V-notch, and a compact U-notch specimen. Specimens were prepared from AS4/3501-6 graphite-epoxy panels, instrumented with conventional strain gage rosettes and with a cross-line moire grating, and loaded in a convenient testing machine. The shear responses obtained for each test method and the two methods of specimen instrumentation were compared. In a second phase of the program the shear responses obtained from Iosipescu V-notch beam specimens were determined for woven fabric geometries of different weave and fiber architectures. Again the responses of specimens obtained from strain gage rosettes and moire interferometry were compared. Additional experiments were performed on a bidirectional cruciform specimen which was also instrumented with strain gages and a moire grating.

Morton, John↗