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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Clock Synchronization Characterization of the Washington DC Metropolitan Area Quantum Network (DC-QNet)

Quantum networking protocols relying on interference and precise time-of-flight measurements require high-precision clock synchronization. This study describes the design, implementation, and characterization of two optical time transfer methods in a metropolitan-scale quantum networking research testbed. With active electronic stabilization, sub-picosecond time deviation (TDEV) was achieved at integration times between 1 s and 10 5 s over 53 km of deployed fiber. Over the same integration periods, 10-picosecond level TDEV was observed using the White Rabbit-Precision Time Protocol (WR-PTP) over 128 km. Measurement methods are described to understand the sources of environmental fluctuations on clock synchronization towards the development of in-situ compensation methods. Path delay gradients, chromatic dispersion, polarization drift, and optical power variations all contributed to clock synchronization errors. The results from this study will inform future work in the development of link noise management methods essential for enabling experimental research in developing practical quantum networking protocols.

PIKTime↗
NASA NTRSDate not supplied

Picosecond Clock Synchronization Across A 7-Node Metropolitan Scale Quantum Network

Quantum networking protocols relying on interference and precise time-of-flight measurements require high precision clock synchronization. This study describes the design, implementation, and characterization of two optical time transfer methods in a metropolitan-scale quantum networking research testbed. The first technique called active electronic stabilization (ELSTAB), was able to achieve sub-picosecond time deviation (TDEV) at integration times between 1 s and 105s over multiple different fiber lengths of both underground and aerial deployed fiber. The second technique, White Rabbit-Precision Time Protocol (WR-PTP), was able to achieve 10-picosecond TDEV’s over similar fiber lengths at comparable integration times. Environmental fluctuations affected the stability of clock synchronization over deployed fiber. These fluctuations resulted in path delay gradients, chromatic dispersion, polarization drift, and optical power variations. The results from this study will inform future work in the development of compensation methods essential for enabling experimental research in developing practical quantum networking protocols.

synchronization↗
NASA NTRS1982

Integrated optics technology study

The status and near term potential of materials and processes available for the fabrication of single mode integrated electro-optical components are discussed. Issues discussed are host material and orientation, waveguide formation, optical loss mechanisms, wavelength selection, polarization effects and control, laser to integrated optics coupling fiber optic waveguides to integrated optics coupling, sources, and detectors. Recommendations of the best materials, technology, and processes for fabrication of integrated optical components for communications and fiber gyro applications are given.

Chen, B.↗
NASA NTRS1993

Device For Perception Of Polarization

Polarized image viewed through rotating polarizing filter appears to pulsate. Optical device enables human observer to perceive polarization of light. Used alone for viewing in real time and/or in conjunction with video or movie camera to record for subsequent detailed quantitative analysis of polarization in scene. Device used in remote sensing to classify portions of scenes according to polarization characteristics, to enhance viewing through atmosphere and oceans and to enhance contrasts. Used to monitor oilspill from air and detect changes in soil moisture and to map wetlands, among many other possible civilian and military applications.

Whitehead, Victor S.↗
NASA NTRS1993

An observational search for CO2 ice clouds on Mars

CO2 ice clouds were first directly identified on Mars by the Mariner 6 and 7 infrared spectrometer limb scans. These observations provided support for early theoretical modeling efforts of CO2 condensation. Mariner 9 IRIS temperature profiles of north polar hood clouds were interpreted as indicating that these clouds were composed of H2O ice at lower latitudes and CO2 ice at higher latitudes. The role of CO2 condensation on Mars has recently received increased attention because (1) Kasting's model results indicated that CO2 cloud condensation limits the magnitude of the proposed early Mars CO2/H2O greenhouse, and (2) Pollack el al.'s GCM results indicated that the formation of CO2 ice clouds is favorable at all polar latitudes during the fall and winter seasons. These latter authors have shown that CO2 clouds play an important role in the polar energy balance, as the amount of CO2 contained in the polar caps is constrained by a balance between latent heat release, heat advected from lower latitudes, and thermal emission to space. The polar hood clouds reduce the amount of CO2 condensation on the polar caps because they reduce the net emission to space. There have been many extensive laboratory spectroscopic studies of H2O and CO2 ices and frosts. In this study, we use results from these and other sources to search for the occurrence of diagnostic CO2 (and H2O) ice and/or frost absorption features in ground based near-infrared imaging spectroscopic data of Mars. Our primary goals are (1) to try to confirm the previous direct observations of CO2 clouds on Mars; (2) to determine the spatial extent, temporal variability, and composition (H2O/CO2 ratio) of any clouds detected; and (3) through radiative transfer modeling, to try to determine the mean particle size and optical depth of polar hood clouds, thus, assessing their role in the polar heat budget.

Bell, James F., III↗
NASA NTRS1998

Polarization Considerations

As light passes through a optical system the reflections and refractions will in general change the polarization state of the light. If we assume that all of the materials in the thin film coatings and substrate are isotropic and homogeneous then calculating the amount of "instrumental" polarization is a relatively straight forward task. In the following sections we will present a of the steps required to perform a 'polarization ray trace' calculation for a single ray and monochromatic and hence polarized light. The thin film portion of the calculation is also shown. The reason for explicitly showing the thin film equations is that there are sign conventions imposed on the boundary value equations by the orientation and handedness of the various coordinate frames which are attached to the geometric rays. The attenuation of light through a optical system, is relatively simple, and requires at the very least a lens (average) reflectivity or transmissivity. Determining the polarization sensitivity of a optical system is still relatively straight forward requiring at least a knowledge of the behavior of the "s" and "p" components at each interface for the chief ray. Determining the thin film induced aberrations of a optical system are somewhat more demanding. Questions about the arithmetic sign of the phase factors and how this relates to the overall "OPD" of a ray are ubiquitous. Many rays are required to construct a wavefront. Thin film codes which modify the OPD's of rays are a requirement for this last mentioned computation. This requires a consistent scheme of coordinate frames and sign conventions and is probably the most demanding task of a polarization ray trace. Only the electric field will used in the discussion. This is not a restriction as the Stokes parameters are functions of the electric field. The following does not attempt to explain, but only to present all of the required concepts and formulas.

Waluschka, Eugene↗
NASA NTRS1986

Stratospheric conductivity variations over thunderstorms

This paper reports the first in-situ observation of variations in the electrical conductivity over thunderstorms at 26 km altitude. The vector electric field, positive and negative polar conductivity, and optical lightning power/flash were measured by payloads on superpressure balloons in the Southern Hemisphere in early 1984. It is found that in 72 percent of the thunderstorm periods observed (or in 23 of 32 periods) there were clear cases of conductivity variations while the balloons were over the thunderstorms. Examples from two separate balloons at widely separated dates and locations showing both daytime and nighttime events are presented. The conductivity measurements are made with the relaxation technique, and the vector field measurements are based on the double Langmuir probe high-impedance method. It is found that the positive and negative conductivity measurements vary independently and have a different temporal profile than the dc electric field. The polar conductivity variations can exceed a factor of 2 at this altitude. In seven of the nine most intense thunderstorm events the total conductivity increased, while in only one of these nine events did it decrease (one event had no change). Implications of these observations for global current patterns are discussed.

Holzworth, R. H.↗
NASA NTRS1993

Optimization of microscopic and macroscopic second order optical nonlinearities

Nonlinear optical materials (NLO) can be used to extend the useful frequency range of lasers. Frequency generation is important for laser-based remote sensing and optical data storage. Another NLO effect, the electro-optic effect, can be used to modulate the amplitude, phase, or polarization state of an optical beam. Applications of this effect in telecommunications and in integrated optics include the impression of information on an optical carrier signal or routing of optical signals between fiber optic channels. In order to utilize these effects most effectively, it is necessary to synthesize materials which respond to applied fields very efficiently. In this talk, it will be shown how the development of a fundamental understanding of the science of nonlinear optics can lead to a rational approach to organic molecules and materials with optimized properties. In some cases, figures of merit for newly developed materials are more than an order of magnitude higher than those of currently employed materials. Some of these materials are being examined for phased-array radar and other electro-optic switching applications.

Marder, Seth R.↗
NASA NTRS1984

F layer ionization patches in the polar cap

Ground-based optical and digital ionosonde measurements were conducted at Thule, Greenland to measure ionospheric structure and dynamics in the nighttime polar cap F layer. These observations showed the existence of large-scale (800-1000 km) plasma patches drifting in the antisunward direction during a moderately disturbed (Kp greater than or equal to 4) period. Simultaneous Dynamics Explorer (DE-B) low-altitude plasma instrument (LAPI) measurements show that these patches with peak densities of about 10 to the 6th el per cu cm are not locally produced by structured particle precipitation. The LAPI measurements show a uniform precipitation of polar rain electrons over the polar cap. The combined measurements provide a comprehensive description of patch structure and dynamics. They are produced near or equatorward of the dayside auroral zone and convect across the polar cap in the antisunward direction. Gradients within the large scale, drifting patches are subject to structuring by convective instabilities. UHF scintillation and spaced receiver measurements are used to map the resulting irregularity distribution within the patches.

Weber, E. J.↗
NASA NTRS1979

Discovery of a soft X-ray flux from AN Ursae Majoris

During November 1975, the soft X-ray detectors on the SAS 3 satellite scanned across AN Ursae Majoris, a star very similar to AM Herculis in its unusual optical properties. A soft (0.1-0.4 keV) X-ray flux averaging 2.8 x 10 to the -11th erg/sq cm-sec was detected from AN UMa, as had been anticipated by analogy with AM Her. Folding the X-ray flux measurement with the known binary period reveals an X-ray light curve with approximately 100% modulation, and thereby secures the identification of the X-ray source as AN UMa. Unlike the case in AM Her, the X-ray minimum in AN UMa occurs midway between optical linear-polarization peaks.

Hearn, D. R.↗
NASA NTRS1981

The MSFC vector magnetograph

The NASA/Marshall Space Flight Center's solar vector magnetograph system allows measurements of all components of the Sun's photospheric magnetic field over a 5 x 5 or 2.5 x 2.5 arc min square field of view with an optimum time resolution of approximately 100 sec and an optimum signal-to-noise of approximately 1000. The basic system components are described, including the optics, detector, digital system, and associated electronics. Automatic sequencing and control functions are outlined as well as manual selections of system parameters which afford unique system flexibility. Results of system calibration and performance are presented, including linearity, dynamic range, uniformity, spatial and spectral resolutions, signal-to-noise, electro-optical retardation and polarization calibration.

Hagyard, M. J.↗
NASA NTRS1984

Local Interstellar Medium. International Astronomical Union Colloquium No. 81

Helium and hydrogen backscattering; ultraviolet and EUV absorption spectra; optical extinction and polarization; hot gases; soft X-ray observations; infrared and millimeter wavelengths; radio wavelengths and theoretical models of the interstellar matter within about 150 parsecs of the Sun were examined.

Kondo, Y.↗
NASA NTRS1989

Planar Poincare chart - A planar graphic representation of the state of light polarization

The planar Poincare chart, which represents the complete planar equivalence of the Poincare sphere, is proposed. The four sets of basic lines are drawn on two separate charts for the generalization and convenience of reading the scale. The chart indicates the rotation of the principal axes of linear birefringent material. The relationships between parameters of the two charts are given as 2xi-2phi (orientation angle of the major axis-ellipticity angle) pair and 2alpha-delta (angle of amplitude ratio-phase difference angle) pair. The results are useful for designing and analyzing polarization properties of optical components with birefringent properties.

Tedjojuwono, Ken K.↗
NASA NTRS1991

THz dichroic plates for use at high angles of incidence

The design of a high frequency dichroic plate consisting of an electrically thick self supporting metallic mesh that can be used in a linearly polarized quasi-optical system at high angles of incidence is described. The measured and computed performance of a 2.5-inch aperture mesh is given. This mesh has a 3-dB cutoff frequency of 875 GHz and less than 0.75 dB of transmission loss from 950-1350 GHz at incidence angles of 0, 30, and 45 degrees. The results of a multimode waveguide analysis corroborate the measured data.

Siegel, Peter H.↗
NASA NTRS1992

Non-mechanical optical path switching and its application to dual beam spectroscopy including gas filter correlation radiometry

A non-mechanical optical switch is developed for alternately switching a monochromatic or quasi-monochromatic light beam along two optical paths. A polarizer polarizes light into a single, e.g., vertical component which is then rapidly modulated into vertical and horizontal components by a polarization modulator. A polarization beam splitter then reflects one of these components along one path and transmits the other along the second path. In the specific application of gas filter correlation radiometry, one path is directed through a vacuum cell and one path is directed through a gas correlation cell containing a desired gas. Reflecting mirrors cause these two paths to intersect at a second polarization beam splitter which reflects one component and transmits the other to recombine them into a polarization modulated beam which can be detected by an appropriate single sensor.

Sachse, Glen W.↗
NASA NTRS1992

Lidar depolarization by nonspherical particles: Potential of combined depolarization/backscattering measurements for PSC's characterization

We analyze the potential of combined backscatter and depolarization information for deriving the optical parameters of Polar Stratospheric Clouds (PSCs) together with the size and physical phase of the cloud particles. In particular, we investigate the influence of particle shape and orientation on the parallel and perpendicular backscattered intensities and on the depolarization ratio under experimental noise conditions, and how the first three moments of the particle size distribution (i.e., particle concentration, mean radius, and standard deviation) may be used to introduce further distinction between type Ia and type Ib PSCs.

Flesia, C.↗