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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

An improved multi-exposure approach for high quality holographic femtosecond laser patterning

High efficiency two photon polymerization through single exposure via spatial light modulator (SLM) has been used to decrease the fabrication time and rapidly realize various micro/nanostructures, but the surface quality remains a big problem due to the speckle noise of optical intensity distribution at the defocused plane. Here, a multi-exposure approach which used tens of computer generate holograms successively loaded on SLM is presented to significantly improve the optical uniformity without losing efficiency. By applying multi-exposure, we found that the uniformity at the defocused plane was increased from ∼0.02 to ∼0.6 according to our simulation. The fabricated two series of letters “HELLO” and “USTC” under single-and multi-exposure in our experiment also verified that the surface quality was greatly improved. Moreover, by this method, several kinds of beam splitters with high quality, e.g., 2 × 2, 5 × 5 Daman, and complex nonseperate 5 × 5, gratings were fabricated with both of high quality and short time (<1 min, 95% time-saving). This multi-exposure SLM-two-photon polymerization method showed the promising prospect in rapidly fabricating and integrating various binary optical devices and their systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1971

The effect of timing errors in optical digital systems

The effects of imperfect timing in direct detection (non-coherent) optical binary systems using both PPM and on-off keying for bit transmission are investigated. Particular emphasis is placed on specification of timing accuracy, and an examination of system degradation when this accuracy is not attained. Bit error probabilities are shown as a function of timing errors, from which average error probabilities can be computed for specific synchronization methods. Of significant importance is the presence of a residual, or irreducible error probability in both systems, due entirely to the timing system, that cannot be overcome by the data channel.

Gagliardi, R.↗
NASA NTRS1972

The effect of timing errors in optical digital systems.

The use of digital transmission with narrow light pulses appears attractive for data communications, but carries with it a stringent requirement on system bit timing. The effects of imperfect timing in direct-detection (noncoherent) optical binary systems are investigated using both pulse-position modulation and on-off keying for bit transmission. Particular emphasis is placed on specification of timing accuracy and an examination of system degradation when this accuracy is not attained. Bit error probabilities are shown as a function of timing errors from which average error probabilities can be computed for specific synchronization methods. Of significance is the presence of a residual or irreducible error probability in both systems, due entirely to the timing system, which cannot be overcome by the data channel.

Gagliardi, R. M.↗
NASA NTRS1974

Threshold detection in an on-off binary communications channel with atmospheric scintillation

The optimum detection threshold in an on-off binary optical communications system operating in the presence of atmospheric turbulence was investigated assuming a poisson detection process and log normal scintillation. The dependence of the probability of bit error on log amplitude variance and received signal strength was analyzed and semi-emperical relationships to predict the optimum detection threshold derived. On the basis of this analysis a piecewise linear model for an adaptive threshold detection system is presented. Bit error probabilities for non-optimum threshold detection system were also investigated.

Webb, W. E.↗
NASA NTRS1975

Threshold detection in an on-off binary communications channel with atmospheric scintillation

The optimum detection threshold in an on-off binary optical communications system operating in the presence of atmospheric turbulence was investigated assuming a poisson detection process and log normal scintillation. The dependence of the probability of bit error on log amplitude variance and received signal strength was analyzed and semi-empirical relationships to predict the optimum detection threshold derived. On the basis of this analysis a piecewise linear model for an adaptive threshold detection system is presented. The bit error probabilities for nonoptimum threshold detection systems were also investigated.

Webb, W. E.↗
NASA NTRS1975

Threshold detection in an on-off binary communications channel with atmospheric scintillation

The optimum detection threshold in an on-off binary optical communications system operating in the presence of atmospheric turbulence has been investigated assuming a Poisson detection process and log normal scintillation. The dependence of the probability of bit error on log amplitude variance and received signal strength has been analyzed, and semi-empirical relationships to predict the optimum detection threshold have been derived. On the basis of this analysis, a piecewise-linear model for an adaptive threshold detection system is presented. The bit-error probabilities for nonoptimum threshold detection systems have also been investigated.

Webb, W. E.↗
NASA NTRS1976

Development and evaluation of a Hadamard transform imaging spectrometer and a Hadamard transform thermal imager

A spectrometric imager and a thermal imager, which achieve multiplexing by the use of binary optical encoding masks, were developed. The masks are based on orthogonal, pseudorandom digital codes derived from Hadamard matrices. Spatial and/or spectral data is obtained in the form of a Hadamard transform of the spatial and/or spectral scene; computer algorithms are then used to decode the data and reconstruct images of the original scene. The hardware, algorithms and processing/display facility are described. A number of spatial and spatial/spectral images are presented. The achievement of a signal-to-noise improvement due to the signal multiplexing was also demonstrated. An analysis of the results indicates both the situations for which the multiplex advantage may be gained, and the limitations of the technique. A number of potential applications of the spectrometric imager are discussed.

Harwit, M.↗
NASA NTRS1976

Hadamard transform imager and imaging spectrometer

An imager and a spectrometric imager, which achieve multiplexing by the use of binary optical encoding masks, have been built and tested. The masks are based on orthogonal, pseudorandom digital codes derived from Hadamard matrices. The spatial (and/or spectral) data are therefore obtained in the form of a Hadamard transform of the spatial (and/or spectral) scene. Computer algorithms are used to decode the data and reconstruct images of the original scene. The hardware, algorithms processing and display facility are described. A number of spatial and spatial/spectral images, obtained in the laboratory, are presented.

Swift, R. D.↗
NASA NTRS1984

A generalization of the near-optimum binary coherent state receiver concept

The structure of a maximum a posteriori decoder is derived for binary optical fields processed according to Kennedy's near-optimum scheme, but operating in the presence of random optical phase-error and interfering background fields. An exact expression is found for the error probability, and examples to illustrate decoder performance under various operating conditions of interest are provided.

Vilnrotter, V. A.↗
NASA NTRS1991

Approach range and velocity determination using laser sensors and retroreflector targets

A laser docking sensor study is currently in the third year of development. The design concept is considered to be validated. The concept is based on using standard radar techniques to provide range, velocity, and bearing information. Multiple targets are utilized to provide relative attitude data. The design requirements were to utilize existing space-qualifiable technology and require low system power, weight, and size yet, operate from 0.3 to 150 meters with a range accuracy greater than 3 millimeters and a range rate accuracy greater than 3 mm per second. The field of regard for the system is +/- 20 deg. The transmitter and receiver design features a diode laser, microlens beam steering, and power control as a function of range. The target design consists of five target sets, each having seven 3-inch retroreflectors, arranged around the docking port. The target map is stored in the sensor memory. Phase detection is used for ranging, with the frequency range-optimized. Coarse bearing measurement is provided by the scanning system (one set of binary optics) angle. Fine bearing measurement is provided by a quad detector. A MIL-STD-1750 A/B computer is used for processing. Initial test results indicate a probability of detection greater than 99 percent and a probability of false alarm less than 0.0001. The functional system is currently at the MIT/Lincoln Lab for demonstration.

Donovan, William J.↗
NASA NTRS1993

Fabrication techniques for very fast diffractive lenses

Aspheric lenses with arbitrary phase functions can be fabricated on thin light weight substrates via the binary optics fabrication technique. However, it is difficult and costly to fabricate a fast lens (f/number less than 1) for use as the shorter wavelengths. The pitch of the masks and the alignment accuracy must be very fine. For a large lens, the space-bandwidth product of the element can also become impractically large. In this paper, two alternate approaches for the fabrication of fast aspheric diffractive lenses are described. The first approach fabricates the diffractive lens interferometrically, utilizing a spherical wavefront to provide the optical power of the lens and a computer generated hologram to create the aspheric components. The second approach fabricates the aspheric diffractive lens in the form if a higher order kinoform which trades groove profile fidelity for coarser feature size. The design and implementation issues for these two fabrication techniques are discussed.

Tai, Anthony M.↗
NASA NTRS1993

Predesign of diamond turned refractive/diffractive elements for IR objectives

Diffractive lenses have arrived. Literally hundreds of papers have been published and technology impact reports have been written about the exciting addition of a new tool for the lens designer. Sophisticated computer programs have been developed to aid in the optimization of these diffractive phase profiles for a wide variety of applications. Now, several fabrication methods are being pursued to produce these diffractive elements economically. The best known process is the etching of a multi-level relief grating, known as binary optics. This process uses sets of computer generated lithographic masks. Another, more recently developed method is Dry Photopolymer Embossing (DPE). This replication process uses master holograms. And now, diamond turning is being applied for the machining of these elements. Diamond turning is especially well suited for infrared optics. As any process has advantages and limitations, so has diamond turning. These advantages and limitations are discussed and general guidelines are presented to aid the designer and systems engineer in the project predesign stage.

Riedl, Max J.↗
NASA NTRS1985

Optical Quantum Receiver For Binary Signals

In quantum optical receiver, both amplitude and phase of received optical signal measured to extract as much information as possible, thereby reducing error probability. Phase-modulated received signal mixed with equal amplitude replica of optical carrier generated in phase locked loop. Two signals interfere with each other at photomultiplier cathode. Probability of error with this scheme close to theoretical minimum and implemented with current technology.

Vilnrotter, V. A.↗
DOE OSTI2016

Generation of Hermite–Gaussian modes of high-power femtosecond laser radiation using binary-phase diffractive optical elements

We present the results of experiments on generation of Hermite–Gaussian modes up to the third order inclusive using binary-phase diffractive optical elements (DOEs) illuminated by subterawatt femtosecond laser pulses. We perform a compariosn of the mode formation using DOEs designed by the kinoform method and the fractional coding technique, when the DOEs are illuminated by both femtosecond radiation and cw laser radiation at close wavelengths. (laser beams)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Generation of equal-intensity coherent optical beams by binary geometrical phase on metasurface

We report here the design and realization of a broadband, equal-intensity optical beam splitter with a dispersion-free binary geometric phase on a metasurface with unit cell consisting of two mirror-symmetric elements. We demonstrate experimentally that two identical beams can be efficiently generated with incidence of any polarization. The efficiency of the device reaches 80% at 1120 nm and keeps larger than 70% in the range of 1000–1400 nm. We suggest that this approach for generating identical, coherent beams have wide applications in diffraction optics and in entangled photon light source for quantum communication.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1979

Mass flow in close binaries - Results of optical and ultraviolet observations

Observational data provide information regarding mass flow in close binaries. Data about origin, condition, and development of circumstellar matter can also be obtained. The investigations are based on an evaluation and correlation of photometric observations and simultaneously made photoelectric and spectrographic observations in the visible spectral range and, in addition, also on satellite observations in the ultraviolet range. Supplementary information concerning the mass flow in close binaries is obtained on the basis of observations related to the X-ray, infrared, and radio range. Suitable theoretical models are employed to interpret the observational data.

Rahe, J.↗
DOE OSTI2019

A Search for Optical Emission from Binary Black Hole Merger GW170814 with the Dark Energy Camera

Binary black hole (BBH) mergers found by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors are of immense scientific interest to the astrophysics community, but are considered unlikely to be sources of electromagnetic emission. To test whether they have rapidly fading optical counterparts, we used the Dark Energy Camera to perform an i-band search for the BBH merger GW170814, the first gravitational wave (GW) detected by three interferometers. The 87 deg 2 localization region (at 90% confidence) centered in the Dark Energy Survey (DES) footprint enabled us to image 86% of the probable sky area to a depth of i ~ 23 mag and provide the most comprehensive data set to search for electromagnetic (EM) emission from BBH mergers. To identify candidates, we perform difference imaging with our search images and with templates from pre-existing Dark Energy Survey (DES) images. The analysis strategy and selection requirements were designed to remove supernovae and to identify transients that decline in the first two epochs. We find two candidates, each of which is spatially coincident with a star or a high-redshift galaxy in the DES catalogs, and they are thus unlikely to be associated with GW170814. Our search finds no candidates associated with GW170814, disfavoring rapidly declining optical emission from BBH mergers brighter than i ~ 23 mag (L optical ~ 5 × 10 41 erg s -1 ) 1–2 days after coalescence. In terms of GW sky map coverage, this is the most complete search for optical counterparts to BBH mergers to date.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Ultraviolet and optical studies of binaries with luminous cool primaries and hot companions. IV - Further IUE detections

We have obtained IUE spectra for 31 middle and late-type giant and supergiant stars whose TD-1 fluxes or ground-based spectra indicate the presence of a hot component, or whose radial velocities indicate an unseen component. Stellar components earlier than type F1 were detected in 22 cases. While 20 of the hot secondaries are seen weakly in optical spectra, two are UV discoveries: HD 58134 and HD 183864. The hot companions are classified accurately by temperature class from their far-UV spectra. The interstellar extinction of each system and the relative luminosities of the components are derived from the UV and optical fluxes, using a new grid of UV intrinsic colors for hot dwarfs. We find that many giant stars apparently have companions which are too hot and hence too luminous for consistency with the primary's spectral classification.

Parsons, Sidney B.↗