Search NASA⌕ Search

SEARCH · Search NASA

Results for “Laser coupling”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28

A photochemical study of the kinetics of the reactions of NH2 with phosphine, ethylene, and acetylene using flash photolysis-laser induced fluorescence

The photochemistry of the reactions of NH2 was investigated in an attempt to explain the existence of an abundance of ammonia in the Jovian atmosphere. The production of ammonia reservoirs from the coupling of ammonia with other atmospheric constituents was considered. The rate constants for the reactions of NH2 radicals with phosphine, acetylene, and ethylene were measured. Flash photolysis was used for the production of NH2 radicals and laser induced fluorescence was employed for radical detection. It was determined that the rates of the reactions were too slow to be significant as a source of ammonia reservoirs in the Jovian atmosphere.

Bosco, S. R.↗

Circular-scan streak tube with solid-state readout

A circular-scan streak tube designed for use in a laser ranging system is described. Electrostatic focusing is used between the photocathode and a microchannel plate, and electrons from the microchannel plate are proximity focused onto an output phosphor screen. Electron beam deflection is achieved by driving two orthogonal sets of deflection plate assemblies in phase quadrature at a frequency of 200 MHz. The light intensity in the output beam trace is measured by using a circular Reticon array of 720 photodiodes, which is fiber-optically coupled to the output phosphor screen of the tube. Sample measurements of frequency-doubled Nd:YAG laser-pulse waveforms are given. Also the output beamwidth has been measured at the 200-MHz deflection frequency. The results suggest a limiting resolution of 33 psec for the circular-scan streak tube used for these tests.

Johnson, C. B.↗

Laser wavelength selector and output coupler

Optical system eliminates displacement occurring when wavelengths are selected in multiple wavelength laser utilizing intracavity wavelength selection by first-order Littrow reflection of plane grating. Output coupling varies direction of output beam as different wavelengths are selected by grating rotation.

Hard, T. M.↗

Analytical study of laser supported combustion waves in hydrogen

A one-dimensional energy equation, with constant pressure and area, was used to model the LSC wave. This equation balances convection, conduction, laser energy absorption, radiation energy loss and radiation energy transport. Solutions of this energy equation were obtained to give profiles of temperature and other properties, as well as the relation between laser intensity and mass flux through the wave. The flow through the LSC wave was then conducted through a variable pressure, variable area streamtube to accelerate it to high speed, with the propulsion application in mind. A numerical method for coupling the LSC wave model to the streamtube flow was developed, and a sample calculation was performed. The result shows that 42% of the laser power has been radiated away by the time the gas reaches the throat. It was concluded that in the radially confined flows of interest for propulsion applications, transverse velocities would be less important than in the unconfined flows where air experiments have been conducted.

Kemp, N. H.↗

A new hydrodynamic analysis of double layers

A genuine two-fluid model of plasmas with collisions permits the calculation of dynamic (not necessarily static) electric fields and double layers inside of plasmas including oscillations and damping. For the first time a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser-produced plasmas showing very high dynamic electric fields in nonlinear force-produced cavitous and inverted double layers in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. Results are the rotation of plasmas in magnetic fields and a new second harmonic resonance, explanation of the measured inverted double layers, explanation of the observed density-independent, second harmonics emission from laser-produced plasmas, and a laser acceleration scheme by the very high fields of the double layers.

Hora, Heinrich↗

Large Telescope Segmented Primary Mirror Alignment

A document discusses a broadband (white light) point source, located at the telescope Cassegrain focus, which generates a cone of light limited by the hole in the secondary mirror (SM). It propagates to the aspheric null-mirror, which is optimized to make all the reflected rays to be normal to the primary mirror (PM) upon reflection. PM retro-reflects the rays back through the system for wavefront analysis. The point source and the wavefront analysis subsystems are all located behind the PM. The PM phasing is absolute (white light) and does not involve the SM. A relatively small, aspheric null-mirror located near the PM center of curvature has been designed to deliver the high level of optical wavefront correction. The phasing of the segments is absolute due to the use of a broadband source. The segmented PM is optically aligned independently and separately from the SM alignment. The separation of the PM segments alignment from the PM to the SM, and other telescope optics alignments, may be a significant advantage, eliminating the errors coupling. The point source of this concept is fully cooperative, unlike a star or laser-generated guide-star, providing the necessary brightness for the optimal S/N ratio, the spectral content, and the stable on-axis position. This concept can be implemented in the lab for the PM initial alignment, or made to be a permanent feature of the space-based or groundbased telescope.

Rud, Mayer↗

Recent Progress in Laboratory Astrophysics and Astrochemistry Achieved with the COSmIC Facility

We describe the characteristics and the capabilities of the laboratory facility, COSmIC, that was developed at NASA Ames to generate, process and analyze interstellar, circumstellar and planetary analogs in the laboratory. COSmIC stands for "Cosmic Simulation Chamber" and is dedicated to the study of neutral and ionized molecules and nanoparticles under the low temperature and high vacuum conditions that are required to simulate various space environments such as diffuse interstellar clouds, circumstellar outflows and planetary atmospheres. COSmIC integrates a variety of state-of-the-art instruments that allow recreating simulated space conditions to generate, process and monitor cosmic analogs in the laboratory. The COSmIC experimental setup is composed of a Pulsed Discharge Nozzle (PDN) expansion, that generates a plasma in the stream of a free supersonic jet expansion, coupled to high-sensitivity, complementary in situ diagnostics: cavity ring down spectroscopy (CRDS) and laser induced fluorescence (LIF) systems for photonic detection, and Reflectron Time-Of-Flight Mass Spectrometer (ReTOF-MS) for mass detection. Recent results obtained using COSmIC will be highlighted. In particular, the progress that has been achieved in the domain of the diffuse interstellar bands (DIBs) and in monitoring, in the laboratory, the formation of circumstellar dust grains and planetary atmosphere aerosols from their gas-phase molecular precursors. Plans for future laboratory experiments on interstellar and planetary molecules and grains will also be addressed, as well as the implications of the studies underway for astronomical observations and past and future space mission data analysis.

Salama, Farid↗

Laser processing of silicon solar cells

Results of a study to utilize an Nd:glass laser for production line annealing of ion implantation induced damage in solar cells are reported. Czochralski-grown and sawn Si wafers 7.6 cm in diam, 0.35 mm thick, were implanted with phosphorus junctions and boron BSFs. Annealing with electron beam, laser, and firing of an Al paste to form the BSFs in different cells was compared. The laser was employed at 1.06 and 0.53 micron and in combination of both, with a 20-50 nsec pulsewidth, and energy densities of 1.2, 1.5, 1.9, and 2.1 J/sq cm. Best optical coupling was observed with the combined wavelengths and a 20 nsec pulse, using energy densities less than 1.5 J/sq cm. Although the Al sintered cells displayed the best characteristics, laser annealing is concluded to offer electrically active, defect-free, shallow junction Si substrates for high efficiency cells.

Katzeff, J. S.↗

Animation graphic interface for the space shuttle onboard computer

Graphics interfaces designed to operate on space qualified hardware challenge software designers to display complex information under processing power and physical size constraints. Under contract to Johnson Space Center, MICROEXPERT Systems is currently constructing an intelligent interface for the LASER DOCKING SENSOR (LDS) flight experiment. Part of this interface is a graphic animation display for Rendezvous and Proximity Operations. The displays have been designed in consultation with Shuttle astronauts. The displays show multiple views of a satellite relative to the shuttle, coupled with numeric attitude information. The graphics are generated using position data received by the Shuttle Payload and General Support Computer (PGSC) from the Laser Docking Sensor. Some of the design considerations include crew member preferences in graphic data representation, single versus multiple window displays, mission tailoring of graphic displays, realistic 3D images versus generic icon representations of real objects, the physical relationship of the observers to the graphic display, how numeric or textual information should interface with graphic data, in what frame of reference objects should be portrayed, recognizing conditions of display information-overload, and screen format and placement consistency.

Wike, Jeffrey↗

Quantum mechanical theory of collisional ionization in the presence of intense laser radiation

The paper presents a quantum mechanical formalism for treating ionizing collisions occurring in the presence of an intense laser field. Both the intense laser radiation and the internal electronic continuum states associated with the emitted electrons are rigorously taken into account by combining discretization techniques with expansions in terms of electronic-field representations for the quasi-molecule-plus-photon system. The procedure leads to a coupled-channel description of the heavy-particle dynamics which involves effective electronic-field potential surfaces and continua. It is suggested that laser-influenced ionizing collisions can be studied to verify the effects of intense laser radiation on inelastic collisional processes. Calculation procedures for electronic transition dipole matrix elements between discrete and continuum electronic states are outlined.

Bellum, J. C.↗

Coupling, Q-Factor, and Integration Aspects of Microsphere Applications

With suggested applications varying from microlaser and cavity QED through optical locking of diode lasers to modulators and sensors, high-Q silica microspheres with whispering-gallery (WG) modes so far remain the subject of tabletop feasibility demonstrations. Despite the uniquely high quality-factor and submillimeter dimensions suitable for tight packaging, this novel type of high-finesse cavity still has to be adapted to fiber- and integrated-optic hardware. In the visible and near infrared-band experiments (633-850nm) measuring the ringdown time tau of free oscillations, Q = (0.6 to 0.8 ) x 10(exp 10) has been obtained in silica spheres of diameter -800 microns (corresponding tau = 3 to 4 microseconds). It was proved that under normal laboratory conditions, quality-factor is subject to deterioration within several-minute scale down to (2 ... 3 ) x 10(exp 9). The responsible mechanism was identified as adsorption of a monolayer of atmospheric water, so that preservation of the ultimate Q requires manipulation in dry environment, or fast packaging into sealed devices. Larger Q can be expected closer to minimum of attenuation in fused silica alpha = 0.2 dB/km; Q greater than or equal to 1 x 10(exp 11) at lambda=1.55 microns, with corresponding energy storage time tau approx. 0.1ms. Experiments are currently underway to determine whether this high Q can be realized experimentally. The evident difficulty is that OH-related optical absorption has its peaks located near the reported minimum of attenuation in silica. We can also mention here that some of proposed fiber materials, yet not ready for fiber drawing, have been predicted to have smaller attenuation than fused silica and may be suitable for microsphere fabrication (sodium-magnesium silicate glass, alpha = 0.06dB/km). WG modes possess very small radiative loss (it does not prevent Q-10(exp 20) and more) and therefore are electromagnetically isolated and cannot be excited by free-space beams. If no modification (such as grating) is made on the sphere surface, the coupling has to he provided by an appropriate near-field device. A systematic theoretical approach has been recently developed to quantify the performance of near-field couplers for WG modes. Efficient coupling can be obtained upon fulfillment of two main conditions: (1) mode matching and (2) sufficient coupling strength to provide the buildup of a WG mode with a given intrinsic loss. In other words, the wave in the coupler has to be phase-matched and sufficiently overlapped with the WG mode to provide enough buildup in the cavity. If the coupling efficiency is characterized by the fractional depth K(sup 2) of the resonance dip in intensity transmittance observed upon varying the frequency of the exciting wave in the coupler.

Ilchenko, V. S.↗

Vaporization of graphite in the temperature range of 4000 to 4500 K

The vaporization of graphite under intense laser radiation is considered both theoretically and experimentally. Under intense radiation, the mass-loss rate can be high enough to cause the flow in the laser plume to be supersonic. It is shown that under these conditions the vaporization process is coupled to the plume gasdynamics and the mass-loss rate for graphite is 62% of the free vaporization rate. Experimental results are presented for surface temperatures from 3985 to 4555 K and mass-loss rates from 0.56 to 27.0 g per sq cm sec. The results are used to determine the vapor pressure of graphite in a pressure range of 2 to 11 atm, and the values are shown to be in agreement with the JANAF vapor pressure curve.

Lundell, J. H.↗

Nondispersive X-ray spectroscopy and imaging of plasmas using a charge-coupled device

A virtual-phase charge-coupled device (CCD) was used to obtain pinhole images and X-ray spectra of laser-produced, solid target plasmas. With the CCD used in the single-photon counting mode, the spectrum in the energy range 2-10 keV was obtained without a dispersive element. Typical spectra reveal two distinct temperatures: a cold component of approximately 200 eV and a hot component of approximately 5 keV. Also, multiline spectra comprising characteristic line emission (K alpha, K beta) from a multilayer target bombarded by beta-rays were recorded using a three-phase CCD. The results demonstrate the potential of CCDs as imaging spectrometers with application in space, laboratory, and fusion-plasma research.

Marsh, K.↗

Frequency stabilization in injection controlled pulsed CO2 lasers

Longitudinal mode selection by injection has been demonstrated as a viable technique for tailoring a TEA-CO2 laser with pulse energies of a Joule or greater to fit the requirements of a coherent lidar transmitter. Once reliable generation of single-longitudinal-mode (SLM) pulses is obtained, one can study the intrapulse frequency variation and attempt to determine the sources of frequency sweeping, or chirp. These sources include the effect of the decaying plasma, the thermal gradient due to the energy dissipation associated with the laser mechanism itself, and the pressure shift of the center frequency of the laser transition. The use of the positive-branch unstable resonator as an efficient means of coupling a discharge with transverse spatial dimensions of the order of centimeters to an optical cavity mode introduces another concern: namely, what can be done to emphasize transverse mode discrimination in an unstable resonator cavity while maintaining high coupling efficiency. These issues are briefly discussed in the paper, and representative experimental examples are included.

Menzies, Robert T.↗

Phase-locked injection laser arrays with variable stripe spacing

A phase-locked injection laser array is described which utilizes variations in spacing of identical lasing elements to vary the coupling between them. A coupled-mode analysis indicates that excellent matching of fundamental array mode to a uniform gain distribution can be obtained. Observation of the array emission patterns confirms the results of the coupled-mode analysis.

Ackley, Donald E.↗

Frequency stabilization and transverse mode discrimination in injection-seeded unstable resonator TEA CO2 lasers

Longitudinal mode selection by injection has been demonstrated as a viable technique for TEA-CO2 lasers with pulse energies of a Joule or greater. Once reliable generation of single-longitudinal-mode (SLM) pulses is obtained, the characteristics and the causes of intrapulse frequency variation can be studied. These include the effect of the decaying plasma, the thermal gradient due to the energy dissipation associated with the laser mechanism itself, and the pressure shift of the center frequency of the laser transition. The use of the positive-branch unstable resonator as an efficient means of coupling a discharge with large spatial dimensions to an optical cavity mode introduces another concern: namely, what can be done to emphasize transverse mode discrimination in an unstable resonator cavity while maintaining high coupling efficiency. These issues are discussed in this paper, and relevant experimental results are included.

Ancellet, G. M.↗

AlGaAs phased array laser for optical communications

Phased locked arrays of multiple AlGaAs diode laser emitters were investigated both in edge emitting and surface emitting configurations. CSP edge emitter structures, coupled by either evanescent waves or Y-guides, could not achieve the required powers (greater than or similar to 500 mW) while maintaining a diffraction limited, single lobed output beam. Indeed, although the diffraction limit was achieved in this type of device, it was at low powers and in the double lobed radiation pattern characteristic of out-of-phase coupling. Grating surface emitting (GSE) arrays were, therefore, investigated with more promising results. The incorporation of second order gratings in distribute Bragg reflector (DBR) structures allows surface emission, and can be configured to allow injection locking and lateral coupling to populate 2-D arrays that should be able to reach power levels commensurate with the needs of high performance, free space optical communications levels. Also, a new amplitude modulation scheme was developed for GSE array operation.

Carlson, N. W.↗

A wide-band monolithic quasi-optical power meter for millimeter- and submillimeter-wave applications

A novel monolithic power meter has been developed for submillimeter-wave applications (100 GHz to 10 THz). The detector is a large-area bismuth bolometer integrated on a 1.2-micron-thick dielectric membrane. This approach results in a wide-band, high-responsivity detector. The power meter is simple to fabricate, is inexpensive, and can be easily calibrated using a low-frequency network. Quasi-optical measurements at 90, 140, and 240 GHz show that the bolometer is polarization-independent and could be modeled by a simple transmission line model. Absolute power measurements at 90, 140, and 240 GHz show a + or - 5 percent accuracy and agree well with a calibrated Anritsu power meter at 90 GHz. Potential application areas are power calibration, antenna coupling efficiency measurements, and absolute power measurements from solid-state devices and far-infrared lasers at submillimeter wavelengths. Absolute output power measurements on a 220-280 GHz tripler using the quasi-optical power meter are presented as an application example.

Ling, Curtis C.↗