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At least 91 records · Page 5

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NASA NTRS1982

Development of a tantalum pentoxide Luneberg lens

A process has been developed for the fabrication of a tantalum pentoxide waveguide Luneburg lens as the input collimator for an optical signal processing circuit on a silicon substrate, such as an integrated wavelength demultiplexer. The development of such a lens involved improvement of the deposition mask profile, reduction of surface scattering by underlaying the lens, reduction of edge scattering by using shims under the mask, and prediction and measurement of the TE-TM polarization aberration. It is shown that polarization aberration significantly affects the design of a demultiplexer system.

Bryan, D. A.↗

NASA NTRS1984

Adaptive spherical lens

This paper reports the creation of a tandem liquid crystal cell arrangement capable of simulating the performance of a spherical lens. Electrical modulation of the index of refraction creates focusing behavior. The modulation is induced by a set of electrodes whose individual voltages are arranged to provide a cylindrical exit wave front for a uniform plane-wave input. Two such cells with orthogonal electrodes arranged in cascade create spherical lens performance. Experimental evidence using a lens with a relatively small number of electrodes is presented. Applications for such structures, once improved, would include real-time focus adjustment for optical disk readers and hand-held photographic equipment as well as aberration compensation for long path-length optical systems.

Kowel, S. T.↗

NASA NTRS1987

Development of a Fresnel lens concentrator for space application

The selected conceptual design of the dome lens photovoltaic concentrator for space applications uses a 3.7 cm square aperture dome lens to focus onto a 0.4 cm active diameter gallium arsenide cell. The selected configuration will provide 91.5 percent lens optical efficiency and 21.4 percent cell efficiency at 100 suns irradiance and 100 C cell temperature, for an overall cell efficiency of 19.6 percent. The selected configuration will tolerate 1 degree tracking errors with negligible loss of performance. The selected panel weight is 2.5 kg/sq.m.

Oneill, Mark J.↗

NASA NTRS1987

Statistical treatment of fluctuations in the gravitational focusing of light due to stellar masses within a gravitational lens

When light from small, distant sources in the universe is gravitationally focused by an intervening galaxy, the gravitational lens can be influenced by the granularity of the matter distribution which is caused by the stellar (or other compact) masses in the galaxy. A largely analytic, statistical calculation for a gravitational lens due to a collection of compact masses - valid for sources of finite size and for large (as well as small) 'optical depths' for the lens - is developed to treat fluctuations in the light caused by such 'microfocusing' effects. Previous treatments have been either numerical simulations of the Monte Carlo type or limited to single-star (i.e., low-optical-depth) effects.

Deguchi, Shuji↗

NASA NTRS1990

Determination of refractive index of a simple negative, positive, or zero power lens using wedged plated interferometer

A nondestructive technique for measuring the refractive index of a negative lens using a wedged plate interferometer is described. The method can be also used for measuring the refractive index of convex or zero power lenses. Schematic diagrams are presented for the use of a wedged plate interferometer for measuring the refractive index of a concave lens and of a convex lens.

Shukla, R. P.↗

NASA NTRS1992

Development of a contact lens quality monitoring system

The quality of contact lens samples depends strongly on their free volume fractions. It is expected that the free volume fraction of the test samples will also impact their attenuation coefficients for soft x rays. Samples with larger free volume fractions should have lower linear attenuation coefficients. Linear attenuation coefficients for Cd-109/Ag-109 x rays have been measured in five contact lens samples. It has been shown that the difference in the linear attenuation coefficients of discs from any given sample are entirely due to the difference in their respective volume fractions. It is therefore concluded that an x ray attenuation measurement system can serve as a quality monitor for contact lens polymers.

Singh, Jag J.↗

NASA NTRS1992

A gravitational lens candidate with an unusually red optical counterpart

The properties of the strong radio source MG0414 + 0534 are described. It is found to display many of the properties expected in a gravitational lens system. At radio wavelengths and 0.5-arcsec resolution, MG0414 + 0534 is made up of four compact components whose unusual configuration and relative flux densities are similar to those found in confirmed four-image gravitational lens systems. At optical wavelengths three objects are detected, consistent with there being optical objects at the positions of the radio components, given the lower optical resolution. The radio and optical centroid positions agree within the astrometric errors, and the relative ordering of the fluxes is the same. The colors and radiooptical spectral indices are similar, but there are differences larger than the photometric errors and the measured variability (about 30 percent). Extinction by dust might simultaneously explain the unusually red color and the absence of light from a lens.

Hewitt, J. N.↗

NASA NTRS1993

Infrared imaging of MG 0414 + 0534 - The red gravitational lens systems as lensed radio galaxies

We present an IR image of the gravitational lens system MG 0414 + 0534, and IR photometry of PG 1115 + 080, H1413 + 117, and Q1429 - 008. The IR of MG 0414 + 0534 shows a morphology that is similar to the radio and optical morphologies. The object is bright (K-prime = 13.7) and extremely red (I-K-prime = 5.7). MG 0414 + 0534 thus becomes the second radio-selected lens system to have very red optical IR colors. When plotted on a color-magnitude diagram of objects from a radio survey, MG 0414 + 0534 and the other very red system, MG 1131 + 0456, lie near the locus of radio galaxies. We therefore suggest that these systems are lensed high-redshift radio galaxies. In general, lensed radio galaxies should be common among lens systems selected from radio surveys, since a high proportion of radio sources are radio galaxies.

Annis, James↗

NASA NTRS1993

Coherent fiber optic sensor for early detection of cataractogenesis in a human eye lens

A lensless backscatter fiber optic probe is used to measure the size distribution of protein molecules inside an excised, but intact, human eye lens. The fiber optic probe, about 5 mm in diameter, can be positioned arbitrarily close to the anterior surface of the eye; it is a trans-receiver, which delivers a Gaussian laser beam into a small region inside the lens and provides a coherent detection of the laser light scattered by the protein molecules in the backward direction. Protein sizes determined from the fast and slow diffusion coefficients show good correlation with the age of the lens and cataractogenesis.

Dhadwal, Harbans S.↗

NASA NTRS1994

Evaluation of lens distortion errors using an underwater camera system for video-based motion analysis

Video-based motion analysis systems are widely employed to study human movement, using computers to capture, store, process, and analyze video data. This data can be collected in any environment where cameras can be located. One of the NASA facilities where human performance research is conducted is the Weightless Environment Training Facility (WETF), a pool of water which simulates zero-gravity with neutral buoyance. Underwater video collection in the WETF poses some unique problems. This project evaluates the error caused by the lens distortion of the WETF cameras. A grid of points of known dimensions was constructed and videotaped using a video vault underwater system. Recorded images were played back on a VCR and a personal computer grabbed and stored the images on disk. These images were then digitized to give calculated coordinates for the grid points. Errors were calculated as the distance from the known coordinates of the points to the calculated coordinates. It was demonstrated that errors from lens distortion could be as high as 8 percent. By avoiding the outermost regions of a wide-angle lens, the error can be kept smaller.

Poliner, Jeffrey↗

NASA NTRS1994

Parameter degeneracy in models of the quadruple lens system Q2237+0305

The geometry of the quadruple lens system Q2237+0305 is modeled with a simple astigmatic lens: a power-law mass distribution: m approximately r(exp beta) with an external shear gamma. The image positions can be reproduced with an accuracy better than 0.01 arcsec for any 0.0 less than or = beta less than or = 1.85 and the corresponding value of gamma = 0.1385-0.0689 beta. This is a factor of approximately 4 more precise than what can be achieved by the best constant stellar mass/L lens models. The image intensity ratios and the time delay ratios are almost constant along our one parameter family of models, but the total magnification varies from 8 to greater than 1000, and the maximum time delay (between leading image B and trailing image C) for H(sub 0) of 75 km/s (Mpc) varies from more than 20 h to about 1.5 h, while beta increases from 0.0 to 1.85.

Wambsganss, Joachim↗

NASA NTRS1994

Large-scale structure effects on the gravitational lens image positions and time delay

We compute the fluctuations in gravitational lens image positions and time delay caused by large-scale structure correlations. We show that these fluctuations can be expressed as a simple integral over the density power spectrum. Using the Cosmic Background Explorer (COBE) normalization we find that positions of objects at cosmological distances are expected to deviate from their true positions by few arcminutes. These deflections are not directly observable. The positions of the images relative to one another fluctuate by a few percent of the relative separation, implying that one does not expect multiple images to be produced by large-scale structure. Nevertheless, the fluctuations are larger than the observational errors on the positions and affect reconstructions of the lens potential. The time delay fluctuations have a geometrical and a gravitational contribution. Both are much larger than the expected time delay from the primary lens, but partially cancel each other. We find that large-scale structure weakly affects the time delay and time delay measurements can be used as a probe of the distance scale in the universe.

Seljak, Uros↗

NASA NTRS1995

The ultraviolet spectrum of the gravitational lens candidate UM 425 = QSO 1120+019: Evidence for broad absorption line (BAL) structure

The UV line profile structure of high-ionization resonance lines found with the International Ultraviolet Explorer (IUE) in the brightest of four multiply imaged sources (images-A) in the candidate gravitational lens UM 425 = QSO 1120+019 indicates broad absorption line (BAL) structure. The deep-broad trough associated with the O IV line extends to velocities approiximately -12,000 km/s, and contains disrete features that suggest multicomponent velocity structure. This structure may include contributions from C IV absorption from the early-type galaxy that is believed to lens UM 425. A strong absorption feature in the blue wing of the Lyman-alpha lambda 1216 emission line may be a Lyman alpha absorption system at a Z(sub Ly alpha) = 1.437 +/- 0.003, or it may be formed by the superposition of the broad N V lambda lambda 1238, 1242 absorption trough on the extended blue emission wing of the QSO Lyman-alpha line. We obtained a redshift of Z(sub QSO) = 1.471 +/- 0.003 from Lyman-alpha lambda 1215, consistent with the redshift found by Meylan and Djorgovski in the optical. The Lyman-alpha line appears unusally weak due to the presence of N V lambda 1240 BAL absorption. A Lyman-limit absorption system at lambda 912 was not observed in the QSO rest frame. The detection of BAL structure in the other weaker ground-state resonance lines of N II (l) and S IV (l) was not found, suggesting these lines are formed in a region that is distinct from the BAL component. Detection of BAL structure in the other fainter images in this system with Hubble Space Telescope (HST) instrumentation, similar to structure observed here in image A, could provide evidence that UM 425 is a gravitational lens.

Michelitsianos, A. G.↗

NASA NTRS2001

Fresnel Lens

Fresnel lenses span the full range of sizes from lens a few micrometers in diameter to lens several meters in diameter. These lenses are utilized in various fields including optical communication, theatrical lighting, office equipment, video entertainment systems, solar concentrators, and scientific research instruments. These lenses function either as diffractive or refractive optical elements depending on the geometrical feature size of the lens. The basic functions of these lenses is described followed by an overview of fabrication methods. A summary of applications is then provided illustrating the rich variety of applications for which fresnel lenses may be designed to fulfill.

Watson, Michael D.↗

NASA NTRS2001

Apparatus for Direct Optical Fiber Through-Lens Illumination of Microscopy or Observational Objects

In one embodiment of the invention, a microscope or other observational apparatus, comprises a hollow tube, a lens mounted to the tube, a light source and at least one flexible optical fiber having an input end and an output end. The input end is positioned to receive light from the light source, and the output end is positioned within the tube so as to directly project light along a straight path to the lens to illuminate an object to be viewed. The path of projected light is uninterrupted and free of light deflecting elements. By passing the light through the lens, the light can be diffused or otherwise defocused to provide more uniform illumination across the surface of the object, increasing the quality of the image of the object seen by the viewer. The direct undeflected and uninterrupted projection of light, without change of direction, eliminates the need for light-deflecting elements, such as beam-splitters, mirrors, prisms, or the like, to direct the projected light towards the object.

Kadogawa, Hiroshi↗

NASA NTRS2001

Adjustable Focus Optical Correction Lens (AFOCL)

This report describes the activities and accomplishments along with the status of the characterization of a PLZT-based Adjustable Focus Optical Correction Lens (AFOCL) test device. The activities described in this report were undertaken by members of the Center for Applied Optics (CAO) at the University of Alabama in Huntsville (UAH) under NASA Contract NAS8-00188. The effort was led by Dr. Bruce Peters as the Principal Investigator and supported by Dr. Patrick Reardon, Ms. Deborah Bailey, and graduate student Mr. Jeremy Wong. The activities outlined for the first year of the contract were to identify vendors and procure a test device along with performing the initial optical characterization of the test device. This activity has been successfully executed and test results are available and preliminary information was published at the SPIE Photonics West Conference in San Jose, January 2001. The paper, "Preliminary investigation of an active PLZT lens," was well received and generated response with several questions from the audience. A PLZT test device has been commercially procured from an outside vendor: The University of California in San Diego (UCSD) in partnership with New Interconnect Packaging Technologies (NIPT) Inc. The device has been subjected to several tests to characterize the optical performance of the device at wavelengths of interest. The goal was to evaluate the AFOCL similar to a conventional lens and measure any optical aberrations present due to the PLZT material as a deviation in the size of the diffraction limited spot (blur), the presence of diffracted energy into higher orders surrounding the focused spot (a variation in Strehl), and/or a variation or spread in the location of the focused energy away from the optical axis (a bias towards optical wedge, spherical, comma, or other higher order aberrations). While data has been collected indicative of the imaging quality of the AFOCL test device, it was not possible to fully characterize the optical performance of the AFOCL alone because there were significant optical distortions due to fabrication related issues.

Peters, Bruce R.↗

NASA NTRS2009

Miniature Wide-Angle Lens for Small-Pixel Electronic Camera

A proposed wideangle lens is shown that would be especially well suited for an electronic camera in which the focal plane is occupied by an image sensor that has small pixels. The design of the lens is intended to satisfy requirements for compactness, high image quality, and reasonably low cost, while addressing issues peculiar to the operation of small-pixel image sensors. Hence, this design is expected to enable the development of a new generation of compact, high-performance electronic cameras. The lens example shown has a 60 degree field of view and a relative aperture (f-number) of 3.2. The main issues affecting the design are also shown.

Mouroulils, Pantazis↗

NASA NTRS2009

Objective Lens Optimized for Wavefront Delivery, Pupil Imaging, and Pupil Ghosting

An interferometer objective lens (or diverger) may be used to transform a collimated beam into a diverging or converging beam. This innovation provides an objective lens that has diffraction-limited optical performance that is optimized at two sets of conjugates: imaging to the objective focus and imaging to the pupil. The lens thus provides for simultaneous delivery of a high-quality beam and excellent pupil resolution properties.

Olzcak, Gene↗