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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
NASA NTRS2018

Polarization-Controlled Directional Multiphoton Photoemission from Hot Spots on Single Au Nanoshells

Directional photoemission from single Au nanoshells is demonstrated in the low-intensity, multiphoton regime. Thisdirectionality is shown to be due to the plasmonic excitation of highly photoemissive, nanometer scale surface regions, which are characterized by correlated momentum mapping, scanning electron microscopy (SEM), and laser polarization-dependence studies. Furthermore, the photoelectron flux from a single nanoshell can be systematically rotated by over 90° in momentum space simply by polarization-controlled coupling to different hot spots. Photoelectrondistributions are directly characterized in momentum space via velocity map imaging (VMI) of the two-dimensional transverse (px, py) momentum components for single nanoshells. For the majority of nanoshells studied, the photoemission is directionally orthogonal to the laser polarization, which implicates nanoscale crevice-shaped "hotspots" clearly observed in the correlated SEM/VMI studies, with the near-field plasmonic nature of these crevices clarified further via finite-element simulations. These results rationalize the large photoemission enhancements observed in previous Au nanoshell studies, but more importantly provide a novel experimental access to directionally tunable electron emission from nanoscale sources. The ability to control photoemission/photocurrent angular distributions at the nanoscale with only modest optical fields indicates a new parameter for optimizing nanoplasmonic system performance and suggests new plasmonic applications such as ultrafast, polarization-controlled photoelectric/photovoltaic switches.

Pettine, Jacob↗
NASA NTRSDate not supplied

Efficient Ho:LuLiF MOPA Laser Transmitter for Space Pathfinder Coherent Wind Lidar

Supported by NASA’s Earth Science Technology Office (ESTO), a new lidar transmitter system is developed under the Wind-Space Pathfinder coherent wind lidar project. It is an efficient Ho:LuLiF master oscillator power amplifier system (MOPA) that is capable of generating 15 watts power and 180 ns pulse width at 200 Hz PRF with excellent beam quality. The laser is injection seeded to provide stable single longitudinal frequency output. The laser beam polarization can be switched between “S” and “P” alternatively. Thus, the “S” and “P” beams can be directed to two separate telescopes at different directions to provide true horizontal wind measurement without a moving part in the lidar system. The laser power, pulse width and beam quality fulfill the space lidar system’s figure-of-merit (FOM) and measurement accuracy requirements.

Coherent laser radar↗
NASA NTRSDate not supplied

Efficient Ho:LuLiF MOPA Laser Transmitter for Space Pathfinder Coherent Wind Lidar

Supported by NASA’s Earth Science Technology Office (ESTO), a new lidar transmitter system is developed under the Wind-Space Pathfinder coherent wind lidar project. It is an efficient Ho:LuLiF master oscillator power amplifier system (MOPA) that is capable of generating 15 watts power and 180 ns pulse width at 200 Hz PRF with excellent beam quality. The laser is injection seeded to provide stable single longitudinal frequency output. The laser beam polarization can be switched between “S” and “P” alternatively. Thus, the “S” and “P” beams can be directed to two separate telescopes at different directions to provide true horizontal wind measurement without a moving part in the lidar system. The laser power, pulse width and beam quality fulfill the space lidar system’s figure-of-merit (FOM) and measurement accuracy requirements.

Coherent Laser Radar↗
NASA NTRS2001

Fast all-optical switch

An apparatus and method wherein polarization rotation in alkali vapors or other mediums is used for all-optical switching and digital logic and where the rate of operation is proportional to the amplitude of the pump field. High rates of speed are accomplished by Rabi flopping of the atomic states using a continuously operating monochromatic atomic beam as the pump.

Shay, Thomas M.↗
NASA NTRS2014

Evaluation of Magnetoresistive RAM for Space Applications

Magnetoresistive random-access memory (MRAM) is a non-volatile memory that exploits electronic spin, rather than charge, to store data. Instead of moving charge on and off a floating gate to alter the threshold voltage of a CMOS transistor (creating different bit states), MRAM uses magnetic fields to flip the polarization of a ferromagnetic material thus switching its resistance and bit state. These polarized states are immune to radiation-induced upset, thus making MRAM very attractive for space application. These magnetic memory elements also have infinite data retention and erase/program endurance. Presented here are results of reliability testing of two space-qualified MRAM products from Aeroflex and Honeywell.

Heidecker, Jason↗
NASA NTRS1979

Antenna feed system for receiving circular polarization and transmitting linear polarization

An invention is described which provides for receiving a circularly polarized signal from an antenna feed connected to orthogonally spaced antenna elements. It also provides for transmitting a linearly polarized signal through the same feed without switches, and without suffering a 3 dB polarization mismatch loss, using an arrangement of hybrid junctions. The arrangement is comprised of two dividing hybrid junctions, each connected to a different pair of antenna elements and a summing hybrid junction. In one version, a receiver is connected to the summing hybrid junction directly. A diplexer is used to connect a transmitter to only one pair of antenna elements. In another version, designated left and right circularly polarized (LCP and RCP) transmitters are connected to the summing hybrid junction by separate diplexers, and separate LCP and RCP sensitive receivers are connected to the diplexers in order to transmit linearly polarized signals using all four antenna elements while receiving circularly polarized signals as before. An orthomode junction and horn antenna may replace the two dividing hybrid junctions and antenna feed.

Seidel, B. L.↗
NASA NTRS1981

Antenna feed system for receiving circular polarization and transmitting linear polarization

An object is to provide for receiving a circularly polarized signal from an antenna feed (10) connected to orthogonally spaced antenna elements (11, 12, 13, 14) and for transmitting a linearly polarized signal through the same feed without switches, and without suffering a 3 dB polarization mismatch loss, using an arrangement of hybrid junctions. The arrangement is comprised of two dividing hybrid junctions (15, 16), each connected to a different pair of antenna elements and a summing hybrid junction (17). In one embodiment, a receiver (18) is connected to the summing hybrid junction directly. A diplexer (19a or 19b) is used to connect a transmitter (20a or 20b) to only one pair of antenna elements. In an alternative embodiment, designated left and right circularly polarized (LCP and RCP) transmitters (21, 22) are connected to the summing hybrid junction by separate diplexers (23, 24), and separate LCP and RCP sensitive receivers (25, 26) are connected to the diplexers in order to transmit linearly polarized signals using all four antenna elements while receiving circularly polarized signals as before. An orthomode junction (30) and horn antenna (32) may replace the two dividing hybrid junctions (15, 16) and antenna feed (10).

Seidel, Boris L.↗
NASA NTRS1995

Remote sensing measurements of atmospheric methane at 2.3 microns with a nonmechanical GFCR

Gas filter correlation radiometer (GFCR) is a passive remote sensing technique used in a variety of atmospheric measurements. In recent years, a nonmechanical optical switching GFCR has been invented and developed at NASA Langley Research Center. The use of a polarization modulator, in conjunction with a polarization beamsplitter, enables rapid optical switching without mechanically moving parts. In comparison with the conventional GFCR, which involves mechanical chopping or switching between two optical paths, the nonmechanical GFCR possesses some very attractive advantages such as fast sampling rate, high reliability, low weight, and long operational life time. In a recent study, we have developed a new GFCR configuration and have fabricated a compact, nonmechanical breadboard instrument. Using this instrument, we have carried out atmospheric methane measurements in the 2.3 micron region. Measurement results are compared with theoretical predictions using the HITRAN database.

Wang, Liang-guo↗
NASA NTRS2013

Chalcogenide Nanoionic-based Radio Frequency Switch

A nonvolatile nanoionic switch is disclosed. A thin layer of chalcogenide glass engages a substrate and a metal selected from the group of silver and copper photo-dissolved in the chalcogenide glass. A first oxidizable electrode and a second inert electrode engage the chalcogenide glass and are spaced apart from each other forming a gap therebetween. A direct current voltage source is applied with positive polarity applied to the oxidizable electrode and negative polarity applied to the inert electrode which electrodeposits silver or copper across the gap closing the switch. Reversing the polarity of the switch dissolves the electrodeposited metal and returns it to the oxidizable electrode. A capacitor arrangement may be formed with the same structure and process.

Nessel, James↗
NASA NTRS2011

Chalcogenide Nanoionic-Based Radio Frequency Switch

A nonvolatile nanoionic switch is disclosed. A thin layer of chalcogenide glass engages a substrate and a metal selected from the group of silver and copper photo-dissolved in the chalcogenide glass. A first oxidizable electrode and a second inert electrode engage the chalcogenide glass and are spaced apart from each other forming a gap there between. A direct current voltage source is applied with positive polarity applied to the oxidizable electrode and negative polarity applied to the inert electrode which electrodeposits silver or copper across the gap closing the switch. Reversing the polarity of the switch dissolves the electrodeposited metal and returns it to the oxidizable electrode. A capacitor arrangement may be formed with the same structure and process.

Nessel, James↗
NASA NTRS2012

Lidar Electro-Optic Beam Switch with a Liquid Crystal Variable Retarder

A document discusses a liquid crystal variable retarder, an electro-optic element that changes the polarization of an optical beam in response to a low-voltage electronic signal. This device can be fabricated so that the element creates, among other states, a half-wave of retardance that can be reduced to a very small retardance. When aligned to a polarized source, this can act to rotate the polarization by 90 in one state, but generate no rotation in the other state. If the beam is then incident on a polarization beam splitter, it will efficiently switch from one path to the other when the voltage is applied. The laser beam switching system has no moving parts, improving reliability over mechanical switching. It is low cost, tolerant of high laser power density, and needs only simple drive electronics, minimizing the required system resources.

Baer, James↗
NASA NTRS1967

Simplified technique demonstrates magnetic domain switching

Light from a conventional photographic light source is polarized and projected through thin samples of gadolinium iron garnet and then observed with a conventional polarizing microscope. A distinctive change in color from red to yellow is observed as the magnetic domains are switched.

Source record↗
NASA NTRS1982

Voltage reapplication rate control for commutation of thyristors

A circuit for commutating a thyristor (21) by shunting its current for a minimum interval, thereby removing sustaining voltage to said thyristor, then subsequently restoring voltage to said thyristor at a predetermined rate, utilizes a series combination of a commutation electronic switch (22) and an isolated dc voltage supply (23) connected in parallel with the thyristor. The voltage supply is arranged with a polarity that permits the current flowing through the thyristor in one direction to be bypassed through the series combination while the commutation switch is turned on and to reverse bias the thyristor when the commutation switch is fully on. A dv/dt control circuit (24) limits the rate of rise of voltage across the commutation switch (22) as it is turned off in response to a command input signal. The dv/dt control circuit is comprised of a constant current drive (31) and a capacitor (32) connected between the output terminal of the commutation switch and the control input terminal of the commutation switch. The thyristor may be a triac (40) with two commutation switches (42, 43), one for current of each polarity, or with a single commutation switch (55) and a bridge circuit (52-55) for selecting the polarity of the switch (56).

Rippel, Wally E.↗
NASA NTRS2006

The Primordial Anisotropy Polarization Pathfinder Array (PAPPA): Instrument Overview and Status

PAPPA is a balloon-based experiment designed to measure the polarization of the Cosmic Microwave Background using candidate technology for an eventual Inflation Probe mission. It will survey a 20 x 20 degree patch of sky with 1 degree angular resolution covering 3 passbands centered at 100,200 and 300 GHz. Detection will be accomplished via antenna-coupled transition edge sensors (TESs) with SQUID-based readouts. In the eventual flight package, band defining filters and MEMS-based polarization modulators will be incorporated into the superconducting microstrip transmission lines that terminate in resistors that are thermally coupled to the TESs. The MEMS switches will allow on-chip polarization modulation that is faster than significant detector gain variations. The initial configuration will incorporate a simplified focal plane augmented by quasioptical polarization modulation. We describe the overall instrument design and present a summary of the current progress.

Chuss, David↗
NASA NTRS1988

Bistable direction switching in an off-axis pumped continuous wave ruby laser

A report is presented of the observation of hysteretic bistable direction switching in a single-mode CW ruby laser system. This effect is only observed when the pump beam which is focused into the ruby rod is misaligned with respect to the rod end faces. At low pump powers, the ruby lases in a mode nearly collinear with the pump axis. At a higher pump power the ruby switches to a mode that is collinear with the rod end faces and preserves the original polarization. The effect is large enough to switch the beam by an angle equal to twice the diffraction angle. The observations show that under steady-state pumping, a CW ruby laser can exhibit bistable operation in its output direction and power. A calculation using the heat equation with two concentric cylinders with one as a heat source (pump laser) and the outer wall of the other held at 77 K, gives an increase in core temperature of about 0.01 K. Therefore, the increase in temperature is not large enough to change the index of refraction to account for such large macroscopic effects.

Afzal, R. Sohrab↗
NASA NTRS1984

Magneto-optic garnet and liquid crystal optical switches

Magnetic stripe domain and liquid crystal devices are being developed and evaluated as fiber optic switches that can be utilized for nonblocking type nxm optical matrix switches in networking and optical processing. Liquid crystal switches are characterized by very low insertion loss and crosstalk, while stripe domain switches commutate in less than one microsecond. Both switches operate on multimode, randomly polarized fiber light with potentially large values for (n,m). The applications of these magnetic stripe domain and liquid crystal devices are discussed.

Krawczak, J. A.↗
NASA NTRS2004

Measuring Radiation Patterns of Reconfigurable Patch Antennas on Wafers

An apparatus and technique have been devised for measuring the radiation pattern of a microwave patch antenna that is one of a number of identical units that have been fabricated in a planar array on a high-resistivity silicon wafer. The apparatus and technique are intended, more specifically, for application to such an antenna that includes a DC-controlled microelectromechanical system (MEMS) actuator for switching the antenna between two polarization states or between two resonance frequencies. Prior to the development of the present apparatus and technique, patch antennas on wafers were tested by techniques and equipment that are more suited to testing of conventional printed-circuit antennas. The techniques included sawing of the wafers to isolate individual antennas for testing. The equipment included custom-built test fixtures that included special signal launchers and transmission-line transitions. The present apparatus and technique eliminate the need for sawing wafers and for custom-built test fixtures, thereby making it possible to test antennas in less time and at less cost. Moreover, in a production setting, elimination of the premature sawing of wafers for testing reduces loss from breakage, thereby enhancing yield.

Simons, Rainee N.↗