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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Study of optimum methods of optical communication

Optimum methods of optical communication accounting for the effects of the turbulent atmosphere and quantum mechanics, both by the semi-classical method and the full-fledged quantum theoretical model are described. A concerted effort to apply the techniques of communication theory to the novel problems of optical communication by a careful study of realistic models and their statistical descriptions, the finding of appropriate optimum structures and the calculation of their performance and, insofar as possible, comparing them to conventional and other suboptimal systems are discussed. In this unified way the bounds on performance and the structure of optimum communication systems for transmission of information, imaging, tracking, and estimation can be determined for optical channels.

Harger, R. O.↗
NASA NTRS2013

Per-Pixel, Dual-Counter Scheme for Optical Communications

Free space optical communications links from deep space are projected to fulfill future NASA communication requirements for 2020 and beyond. Accurate laser-beam pointing is required to achieve high data rates at low power levels.This innovation is a per-pixel processing scheme using a pair of three-state digital counters to implement acquisition and tracking of a dim laser beacon transmitted from Earth for pointing control of an interplanetary optical communications system using a focal plane array of single sensitive detectors. It shows how to implement dim beacon acquisition and tracking for an interplanetary optical transceiver with a method that is suitable for both achieving theoretical performance, as well as supporting additional functions of high data rate forward links and precision spacecraft ranging.

Farr, William H.↗
DOE OSTI2023

Meta-optics-based systems and methods for ocular applications

Meta-lens based ocular imaging, near-eye display, and eye-tracking systems are described. The systems can include a single focusing optic and an integrated circuit that provides illumination light and includes an imaging array. The focusing optic includes meta-atoms formed on a substrate. The systems may have no moving parts and achieve imaging or image-projection fields-of-view approaching or exceeding 180 degrees. Because of their low part count, the systems can be robust and have a very small form factor.

Hu, Juejun↗
NASA NTRS1991

Improved accuracies for satellite tracking

A charge coupled device (CCD) camera on an optical telescope which follows the stars can be used to provide high accuracy comparisons between the line of sight to a satellite, over a large range of satellite altitudes, and lines of sight to nearby stars. The CCD camera can be rotated so the motion of the satellite is down columns of the CCD chip, and charge can be moved from row to row of the chip at a rate which matches the motion of the optical image of the satellite across the chip. Measurement of satellite and star images, together with accurate timing of charge motion, provides accurate comparisons of lines of sight. Given lines of sight to stars near the satellite, the satellite line of sight may be determined. Initial experiments with this technique, using an 18 cm telescope, have produced TDRS-4 observations which have an rms error of 0.5 arc second, 100 m at synchronous altitude. Use of a mosaic of CCD chips, each having its own rate of charge motion, in the focal place of a telescope would allow point images of a geosynchronous satellite and of stars to be formed simultaneously in the same telescope. The line of sight of such a satellite could be measured relative to nearby star lines of sight with an accuracy of approximately 0.03 arc second. Development of a star catalog with 0.04 arc second rms accuracy and perhaps ten stars per square degree would allow determination of satellite lines of sight with 0.05 arc second rms absolute accuracy, corresponding to 10 m at synchronous altitude. Multiple station time transfers through a communications satellite can provide accurate distances from the satellite to the ground stations. Such observations can, if calibrated for delays, determine satellite orbits to an accuracy approaching 10 m rms.

Kammeyer, P. C.↗
NASA NTRS2024

Convective Characteristics and GOES GLM Optical Energy in Hurricane Ian (2022)

Tropical cyclone (TC) track forecasts have improved greatly in recent decades, while intensity forecasts have struggled to improve at the same rate. As a result, there has been a focus in literature to attempt to better understand the processes that lead to TC intensification and especially TC rapid intensification (RI). Lightning has been studied as a tool to determine changes in TC intensity, but studied thus far have had conflicting results.

Hurricane↗
NASA NTRS2000

Scanning Lidar Transceiver Telescopes Using Holographic Optical Elements

Scanning enables remote measurements perpendicular to the ground track of airborne and spaceborne lidar systems, giving us three dimensional images of atmospheric backscatter or other measurable parameters. For ground based systems, scanning allows one to record a time series of data in multiple spatial dimensions. The large size and cost of scanning systems for atmospheric lidars using conventional scanning technologies is prohibitive for space based systems. By replacing the conventional reflective telescope with a holographic optical element (HOE) in the lidar, single axis conical scanning can be achieved with a mechanically simple system. Relatively inexpensive to produce, HOES can be used to satisfy a variety of scanning lidar applications. I will introduce the concept of the HOE and describe its production and use as a scanning lidar transceiver telescope. I will describe the advantages as well as the disadvantages and limitations of HOES in this application. Optical performance test results and two lidar systems currently using HOES will be described. Examples of data taken with these systems will be presented. Current and planned future developments will be described, including scanning without mechanical motion and wide field-of-view lidar imaging.

Schwemmer, Geary K.↗
NASA NTRS1994

Lasercom system architecture with reduced complexity

Spatial acquisition and precision beam pointing functions are critical to spaceborne laser communication systems. In the present invention, a single high bandwidth CCD detector is used to perform both spatial acquisition and tracking functions. Compared to previous lasercom hardware design, the array tracking concept offers reduced system complexity by reducing the number of optical elements in the design. Specifically, the design requires only one detector and one beam steering mechanism. It also provides the means to optically close the point-ahead control loop. The technology required for high bandwidth array tracking was examined and shown to be consistent with current state of the art. The single detector design can lead to a significantly reduced system complexity and a lower system cost.

Lesh, James R.↗
NASA NTRS1996

LaserCom System Architecture With Reduced Complexity

Spatial acquisition and precision beam pointing functions are critical to spaceborne laser communication systems. In the present invention a single high bandwidth CCD detector is used to perform both spatial acquisition and tracking functions. Compared to previous lasercom hardware design, the array tracking concept offers reduced system complexity by reducing the number of optical elements in the design. Specifically, the design requires only one detector and one beam steering mechanism. It also provides means to optically close the point-ahead control loop. The technology required for high bandwidth array tracking was examined and shown to be consistent with current state of the art. The single detector design can lead to a significantly reduced system complexity and a lower system cost.

Lesh, James R.↗
NASA NTRS1993

Optical imaging chamber for X-ray astronomy

The light emitted by electron avalanches in a parallel plate chamber can be used to image the tracks of photoelectrons liberated by the interaction of an incident X-ray with the gas filling the chamber. The differing morphologies of photoelectron tracks and high-energy charged particle tracks can be used for background rejection. The initial direction (before scattering) of the liberated photoelectron also contains information about the polarization of the incident radiation. We have built a small test chamber with which we have imaged photoelectron tracks using an intensified CCD camera. Our results show that optical imaging could be used in a hard X-ray imaging polarimeter useful for astronomy.

Austin, Robert A.↗
NASA NTRS1972

A 10, 6-micrometer laser receiver RF subsystem

A simplified laser receiver carrier tracking loop is described. The laser carrier is optically mixed with a locally generated 10.6 micrometer signal, thereby translating the received signal to an IF signal that varies between dc and GHz. This signal is fed to a second order carrier tracking loop that contains a transistor LC oscillator tuned by a varactor over a 1 GHz range; transistor shunt capacitance increases the upper frequency bound of the oscillator in a high Doppler environment.

Santarpia, D. E.↗
NASA NTRS1990

Tracking and letter classification under dichoptic and binocular viewing conditions

Subjects were required to fly a simulated helicopter path, while also classifying letter pairs presented intermitently at 5 retinal locations. Binocular and Dichoptic conditions were compared by employing color filters. Tracking under dichoptic conditions was strongly influenced by the absence of a common optical axis. Classification performance also deteriorated and was influenced by the conditions of tracking.

Gopher, Daniel↗
NASA NTRS1985

The Nagoya cosmic-ray muon spectrometer 3, part 4: Track reconstruction method

One of the greatest problems in measuring particle trajectories with an optical or visual detector system, is the reconstruction of trajectories in real space from their recorded images. In the Nagoya cosmic-ray muon spectrometer, muon tracks are detected by wide gap spark chambers and their images are recorded on the photographic film through an optical system of 10 mirrors and two cameras. For the spatial reconstruction, 42 parameters of the optical system should be known to determine the configuration of this system. It is almost impossible to measure this many parameters directly with usual techniques. In order to solve this problem, the inverse transformation method was applied. In this method, all the optical parameters are determined from the locations of fiducial marks in real space and the locations of their images on the photographic film by the non-linear least square fitting.

Shibata, S.↗
NASA NTRS2000

Retrieving the Vertical Structure of the Effective Aerosol Complex Index of Refraction from a Combination of Aerosol in Situ and Remote Sensing Measurements During TARFOX

The largest uncertainty in estimates of the effects of atmospheric aerosols on climate stems from uncertainties in the determination of their microphysical properties, including the aerosol complex index of refraction, which in turn determines their optical properties. A novel technique is used to estimate the aerosol complex index of refraction in distinct vertical layers from a combination of aerosol in situ size distribution and remote sensing measurements during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). In particular, aerosol backscatter measurements using the NASA Langley LASE (Lidar Atmospheric Sensing Experiment) instrument and in situ aerosol size distribution data are utilized to derive vertical profiles of the "effective" aerosol complex index of refraction at 815 nm (i.e., the refractive index that would provide the same backscatter signal in a forward calculation on the basis of the measured in situ particle size distributions for homogeneous, spherical aerosols). A sensitivity study shows that this method yields small errors in the retrieved aerosol refractive indices, provided the errors in the lidar-derived aerosol backscatter are less than 30% and random in nature. Absolute errors in the estimated aerosol refractive indices are generally less than 0.04 for the real part and can be as much as 0.042 for the imaginary part in the case of a 30% error in the lidar-derived aerosol backscatter. The measurements of aerosol optical depth from the NASA Ames Airborne Tracking Sunphotometer (AATS-6) are successfully incorporated into the new technique and help constrain the retrieved aerosol refractive indices. An application of the technique to two TARFOX case studies yields the occurrence of vertical layers of distinct aerosol refractive indices. Values of the estimated complex aerosol refractive index range from 1.33 to 1.45 for the real part and 0.001 to 0.008 for the imaginary part. The methodology devised in this study provides, for the first time, a complete set of vertically resolved aerosol size distribution and refractive index data. yielding the vertical distribution of aerosol optical properties required for the determination of aerosol-induced radiative flux changes.

Redemann, J.↗
NASA NTRS2000

Retrieving the Vertical Structure of the Effective Aerosol Complex Index of Refraction from a Combination of Aerosol in Situ and Remote Sensing Measurements During TARFOX

The largest uncertainty in estimates of the effects of atmospheric aerosols on climate stems from uncertainties in the determination of their microphysical properties, including the aerosol complex index of refraction, which in turn determines their optical properties. A novel technique is used to estimate the aerosol complex index of refraction in distinct vertical layers from a combination of aerosol in situ size distribution and remote sensing measurements during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). In particular, aerosol backscatter measurements using the NASA Langley LASE (Lidar Atmospheric Sensing Experiment) instrument and in situ aerosol size distribution data are utilized to derive vertical profiles of the 'effective' aerosol complex index of refraction at 815 nm (i.e., the refractive index that would provide the same backscatter signal in a forward calculation on the basis of the measured in situ particle size distributions for homogeneous, spherical aerosols). A sensitivity study shows that this method yields small errors in the retrieved aerosol refractive indices, provided the errors in the lidar derived aerosol backscatter are less than 30% and random in nature. Absolute errors in the estimated aerosol refractive indices are generally less than 0.04 for the real part and can be as much as 0.042 for the imaginary part in the case of a 30% error in the lidar-derived aerosol backscatter. The measurements of aerosol optical depth from the NASA Ames Airborne Tracking Sunphotometer (AATS-6) are successfully incorporated into the new technique and help constrain the retrieved aerosol refractive indices. An application of the technique to two TARFOX case studies yields the occurrence of vertical layers of distinct aerosol refractive indices. Values of the estimated complex aerosol refractive index range from 1.33 to 1.45 for the real part and 0.001 to 0.008 for the imaginary part. The methodology devised in this study provides, for the first time a complete set of vertically resolved aerosol size distribution and refractive index data, yielding the vertical distribution of aerosol optical properties required for the determination of aersol-induced radiative flux changes

Redemann, J.↗
NASA NTRS1999

Characterization of Optical Lenses to be Considered for the Imaging of Crystal Dendrite Growth

Dynamic fracture is a phenomenon that is extremely sensitive to small perturbations in system parameters. This phenomenon is, in some ways, similar to that of dendritic crystal growth, although it is governed by different physical principles. Crystal dendrite growth patterns are affected by parameters such as temperature, pressure, and gravity. By studying the behavior of crystal dendrites in a controlled, microgravity environment, a greater understanding of dynamic fracture could be revealed. A sealed cubical container contains four stingers, which facilitate the growth of crystal dendrites. The container has five windows and is emersed in a liquid, for thermal isolation. The tip of a dendrite can advance in any direction, therefore three-dimensional images of the process are desired. Furthermore, because of the rapid growth rate, a fast image frame rate is required for accurate tracking of dendrite tip velocity. In addition, optical parameters such as field of view, depth of focus, and resolution are examined, as well as the working distance between a lens and the target of observation.

Wing, Frank M.↗
DOE OSTI2021

Facile Measurement of the Rotation of a Single Optically Trapped Nanoparticle Using the Diagonal Ratio of a Quadrant Photodiode

Optical tweezers are a powerful tool for exploring physical properties of particles in various environments through analysis of their dynamics in a trapping potential. Analysis of the trapped particle's position is often done using interferometric back-focal-plane detection microscopy in which interference between the trapping laser and the light interacting with the trapped particle is projected on a quadrant photo-diode (QPD). The QPD measurements are almost universally the voltage ratios between the transverse components of the detector (left/right; up/down) that are calibrated to ascertain particle positions and orientations (i.e., rotation). In this paper, we demonstrate how measuring the diagonal ratio of the QPD allows tracking the spinning and orbital motion of optically trapped objects with enhanced sensitivity compared to the conventional transverse ratio and reveals additional information about particle dynamics. The diagonal ratio "balances" the signal from opposite sides of the QPD, allowing common mode noise reduction and increased measurement sensitivity of the rotating nanospheres at frequencies from below 200 Hz to above 15 kHz. We show that the variability in particle rotation rates is due to slight differences in the aspect ratio of the nanoparticles. We also measure in situ a gradual acceleration in the spinning frequency of trapped nanoparticles due to photothermal shedding of surface ligands and the resulting decrease of rotational friction in solution. The accelerating particles spin at rates exceeding 30 kHz and are eventually "optically printed" onto the glass coverslip on top of the liquid cell enclosure. The diagonal ratio is a simple, readily available, and powerful enabler for measuring rotational dynamics with a 5-fold sensitivity increase over conventional QPD measurements. This affords opportunities for controlling the orientational dynamics of trapped nanoparticles, which is crucial for various applications, including nanoscale mechanical motors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1985

A comparison of 8.415-, 32.0- and 565646-GHz deep space telemetry links

An economic and performance comparison is made of spacecraft telecommunication links at 8.415, 32.0, and 565646 GHz (0.53-micron wavelength) for the return of 3.43 x 10 to the 11th power bits from a Saturn Orbiter/Titan Probe mission in year 2000. Technical performance and costs for both ends of the links are included. Spacecraft antenna or telescope efficiencies, pointing losses, ground-based or Earth-orbiting relay terminals efficiencies, noise temperatures, recurring and nonrecurring engineering, and maintenance and operations costs are modeled. Weather effects, dc-to-RF or laser power conversion efficiencies, gravity and other environment distortions gain reductions, and the cost of pointing and tracking are analyzed. The effort is focused primarily on the microwave frequency links. There are large uncertainties in the cost results, but conclusions indicate that for a mid-1990's launch, the Ka-band system is as cost effective as X-band. The Ka-band system has a data rate advantage as compared to the X-band system for the same dc power input to the spacecraft. The magnitude of the advantage is a complex function of the weather at the DSN stations and the elevation angle of the ground antenna. A simple numerical comparison of the advantage is difficult and curves are provided. The optical frequency link is more costly based on the launch-to-orbit costs for the orbiting terminal. A more detailed study of the optical system is recommended to quantify astrometric tracking benefits and improve the accuracy of the cost estimate.

Dickinson, R. M.↗