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At least 433 records · Page 24

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NASA NTRS1991

A lunar rover powered by an orbiting laser diode array

A conceptual design of a high-power, long-duration lunar rover powered by a laser beam is proposed. The laser transmitter in lunar orbit consists of an SP-100 nuclear reactor prime power source providing 100 kW of electricity to a laser array that emits 50 kW of laser radiation. The laser radiation is beamed to the lunar surface where it is received by a GaAlAs solid-state, laser-to-electric converter. This converter provides 22 kW of electrical power to the rover vehicle for science, locomotion, and crew needs. The mass of the laser transmitter is approximately 5000 kg, whereas the mass of the rover power supply is 520 kg. The rover power unit is significantly less massive than alternative rover power units.

De Young, R. J.↗

NASA NTRS1973

Monitoring atmospheric pollutants with a heterodyne radiometer transmitter-receiver

The presence of selected atmospheric pollutants can be determined by transmitting an infrared beam of proper wavelength through the atmosphere, and detecting the reflections of the transmitted beam with a heterodyne radiometer transmitter-receiver using part of the laser beam as a local oscillator. The particular pollutant and its absorption line strength to be measured are selected by the laser beam wave length. When the round-trip path for the light is known or measured, concentration can be determined. Since pressure (altitude) will affect the shape of the molecular absorption line of a pollutant, tuning the laser through a range of frequencies, which includes a part of the absorption line of the pollutant of interest, yields pollutant altitude data from which the altitude and altitude profile is determined.

Menzies, R. T.↗

DOE OSTI2021

Resistive AC-Coupled Silicon Detectors: principles of operation and first results from a combined analysis of beam test and laser data

This paper presents the principles of operation of Resistive AC-Coupled Silicon Detectors (RSDs) and measurements of the temporal and spatial resolutions using a combined analysis of laser and beam test data. RSDs are a new type of n-in-p silicon sensor based on the Low-Gain Avalanche Diode (LGAD) technology, where the n+ implant has been designed to be resistive, and the read-out is obtained via AC-coupling. The truly innovative feature of RSD is that the signal generated by an impinging particle is shared isotropically among multiple read-out pads without the need for floating electrodes or an external magnetic field. Careful tuning of the coupling oxide thickness and the n+ doping profile is at the basis of the successful functioning of this device. Several RSD matrices with different pad width-pitch geometries have been extensively tested with a laser setup in the Laboratory for Innovative Silicon Sensors in Torino, while a smaller set of devices have been tested at the Fermilab Test Beam Facility with a 120 GeV/c proton beam. The measured spatial resolution ranges between 2.5μm for 70–100 pad-pitch geometry and 17μm with 200–500 matrices, a factor of 10 better than what is achievable in binary read-out (bin size/12). Beam test data show a temporal resolution of ~40ps for 200 μm pitch devices, in line with the best performances of LGAD sensors at the same gain.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1984

Measurement of temperature and density fluctuations in turbulence using an ultraviolet laser

Noninvasive measurement of density and temperature fluctuations in turbulent air flow was examined. The approach used fluorescence of oxygen molecules which are selectively excited by a tunable vacuum ultraviolet laser beam. The strength of the fluorescence signal and its dependence on laser wavelength vary with the density and temperature of the air in the laser beam. Because fluorescence can be detected at 90 degrees from the beam propagation direction, spatial resolution in three dimensions, rather than path-integrated measurements can be achieved. With spatial resolutions of the order of a millimeter and at supersonic air velocities it is necessary to perform each measurement in a time of the order of a microsecond; this is possible by by using laser pulses of ten nanosecond duration. In this method atmospheric O2 is excited by the emission of a tunable ArF excimer laser, and the fluorescence, which spans the 210 to 420 range, is detected by an ultraviolet phototube.

Massey, G. A.↗

NASA NTRS2001

All-Optical Micro Motors Based on Moving Gratings in Photosensitive Media

An all-optical micromotor with a rotor driven by a traveling wave of surface deformation of a stator being in contact with the rotor is being studied. Instead of an ultrasonic wave produced by an electrically driven piezoelectric actuator as in ultrasonic motors, the wave is a result of a photo-induced surface deformation of a photosensitive material produced by an incident radiation. A thin piezoelectric polymer will deform more easily LiNbO3 or metal when irradiated with light. The type of photosensitive material studied are piezoelectric polymers with and without coatings for connecting electrodes. In order to be considered as a possible candidate for micromotors, the material should exhibit surface deformation produced by a laser beam of the order of 10 microns. This is compared to the deformations produced by static holographic gratings studied in photorefractive crystals of LiNbO3 using high vertical resolution surface profilometer Dektak 3 and surface interferometer WYKO. An experimental setup showing the oscillations has been developed. The setup uses a chopped beam from an Argon ion laser to produce the deformation while a probe beam is reflected by the thin film into a fiber which is then detected on an oscilloscope. A ramp voltage signal generator will drive the piezoelectric film in another experiment to determine the resonance of the film. A current is generated when light is incident upon the film and this current can be measured. The reverse process has already been demonstrated in other piezoelectric actuators. Changing voltage, polarity, and frequency of the signal can easily generate vibrations similar to those when light is incident on the film. This can be compared to the effects of laser interaction with light absorbing fluids such as solutions of 2,9,16,23-Tetrakis(phenylthio)-29H, 31 H-phthalocyanine in chlorobenzene in capillary tubes, The possibility of using a liquid with the piezoelectric film would be a novel idea for a micromotor since the interaction of a single low power focused laser beam at 633 nm with such fluid produced an intensive circular motion.

Curley, M.↗

NASA NTRS1993

Results from the Galileo Laser Uplink: A JPL Demonstration of Deep-Space Optical Communications

The successful completion of the Galileo Optical Experiment (GOPEX), represented the accomplishment of a significant milestone in JPL's optical communication plan. The experiment demonstrated the first transmission of a narrow laser beam to a deep-space vehicle. Laser pulses were beamed to the Galileo spacecraft by Earth-based transmitters at the Table Mountain Facility (TMF), California, and Starfire Optical Range (SOR), New Mexico. The experiment took place over an eight-day period (December 9 through December 16, 1992) as Galileo receded from Earth on its way to Jupiter, and covered ranges from 1 to 6 million kilometers (15 times the Earth-Moon distance), the laser uplink from TMF covered the longest known range for laser beam transmission and detection. This demonstration is the latest in a series of accomplishments by JPL in the development of deep-space optical communications technology.

Lasers experiment optical communications Galileo d↗

NASA NTRS1986

OH measurement by laser light absorption

Since the first attempt to measure atmospheric hydroxyl radicals by optical absorption in 1975 (Perner et al., 1976) this method has been continuously developed further and its major obstacles and limitations are known today. The laser beam needs to be expanded in order to reduce the beam divergence. At the same time the energy density of the laser beam which produces OH via ozone photolysis is reduced to such an extent that the self-produced OH concentration ranges well below the atmospheric value. Atmospheric absorptions should be observed over a wide spectral range so that not only the OH radicals are properly identified by several rotational lines but their absorption can be corrected for interfering absorptions from other air constituents as SO2, CH2O, CS2, etc., which can be identified in a wide spectral range with more confidence. Air turbulence demands fast spectral scanning or probing on and off the absorption line. Energy requirements should be kept small in field operations. In the experiment frequency doubled dye laser pulses at 308 nm are produced. The picosecond light pulses are expected to show a smooth profile (light intensity against wavelength) which will be broadened to the required spectral width according to the uncertainty principle. The pump laser will be an optoacoustically modulated Nd:YAG laser.

Perner, D.↗

NASA NTRS1974

Effects of viscoelasticity on cavitation in drag reducing fluids

To study cavitation inception in polymer solutions, a blow-down water tunnel with short running times was used. Tests were made using 1/4 and 1/2 inch diameter models of hemispherical-nose cylinders. To accurately detect the inception of cavitation, a reliable technique was developed using a continuously operating He-Ne gas laser. The laser beam was adjusted to grazing incidence with the model at the minimum pressure point where cavitation inception was to be expected. A sensitive photocell was placed at ninety degrees to detect the beam. As incipient cavitation occurred, the bubbles caused scattering of the laser beam which was picked up by the photocell. Static pressure near the model in the working section of the tunnel was measured using a solid-state pressure pick-up. The signals from the photocell and the pressure pick-up were recorded on an oscillograph. Velocity field visualization was achieved using one microsecond duration light pulses scattered by small polystryrene latex spheres in the flow.

Ting, R. Y.↗

NASA NTRS1986

Tracking System for Infrared Spectrometer

Visible laser tracking system for infrared laser spectometer keeps probe infrared laser beam aimed at moving reflector, thereby keeping reflector image and return laser beam within spectrometer field of view. System includes tracking mirror tilted by stepping motors under microprocessor control to deflect beams toward continually changing reflector position.

Johnson, R. A.↗

NASA NTRS2016

Beaconless Pointing for Deep-Space Optical Communication

Free space optical communication is of interest to NASA as a complement to existing radio frequency communication methods. The potential for an increase in science data return capability over current radio-frequency communications is the primary objective. Deep space optical communication requires laser beam pointing accuracy on the order of a few microradians. The laser beam pointing approach discussed here operates without the aid of a terrestrial uplink beacon. Precision pointing is obtained from an on-board star tracker in combination with inertial rate sensors and an outgoing beam reference vector. The beaconless optical pointing system presented in this work is the current approach for the Integrated Radio and Optical Communication (iROC) project.

free-space optical communication↗

NASA NTRS1987

The laser elevator - Momentum transfer using an optical resonator

In a conventional laser lightsail system the payload is propelled by the momentum imparted to it by the reflection of a laser beam without the use of any propellant. Because of the unfavorable relationship between energy and momentum in a light beam, these systems are very inefficient. The efficiency can be greatly improved, in principle, if the photons that impact the payload mirror are returned to the source and then redirected back toward the payload again. This system, which recirculates the laser beam, is defined as the 'laser elevator'. The gain of the laser elevator over conventional lightsails depends on the number of times the beam is recycled which is limited by the reflectance of the mirrors used, any losses in the transmission of the beam, and diffraction. Due to the increase pathlength of the folded beam, diffraction losses occur at smaller separations of the payload and the source mirror than for conventional lightsail system. The laser elevator has potential applications in launching to low earth orbit, orbital transfer, and rapid interplanetary delivery of small payloads.

Meyer, Thomas R.↗

NASA NTRS1980

Cycle II.5 aircraft aero-optical turbulent boundary-layer/shear-layer measurements

The aero-optical effects associated with propagating a laser beam through aircraft turbulent boundary layers and shear layers were examined. Observed laser optical performance levels were compared with those inferred from aerodynamic measurements of unsteady densities and correlation lengths within these random flows. Optical instrumentation included a fast shearing interferometer (FSI). A 9 cm diameter collimated helium neon laser beam made a double pass through the aircraft random flow via an airfoil mirror located one meter from the fuselage. Typical aircraft turbulent boundary layer thickness measured 0.3 meters. Averaging many FSI generated modulation transfer functions (MTFs) and Fourier transforming, this average yields the expected far field intensity degradation associated with an aircraft mounted laser system. Aerodynamic instrumentation included fine wire probes to measure unsteady temperature and mass flux. A laser doppler velocimeter measured unsteady velocity within the flows. An analysis of these data yielded point measurements of unsteady density and correlation length.

Gilbert, K.↗

NASA NTRS1972

Laser propulsion

The use of an earth-based high-power laser beam to provide energy for earth-launched rocket vehicle is investigated. The laser beam energy is absorbed in an opaque propellant gas and is converted to high-specific-impulse thrust by expanding the heated propellant to space by means of a nozzle. This laser propulsion scheme can produce specific impulses of several thousand seconds. Payload to gross-weight fractions about an order of magnitude higher than those for conventional chemical earth-launched vehicles appear possible. There is a potential for a significant reduction in cost per payload mass in earth orbit.

Rom, F. E.↗

NASA NTRS1997

Apparatus and method for high-speed characterization of surfaces

This invention permits rapid determination of a three-dimensional contour of an object. The apparatus directs a laser beam onto a point on an object, and the scattered light is received by a position sensitive detector (PSD). The location at which scattered light is received can be related to the displacement of the point on the object, using basic trigonometry. The laser beam is deflected non-mechanically, by passing it through a crystal whose index of refraction is varied in a controlled manner. By proper control of the index of refraction, one can scan the beam across a desired area of the object, without using any moving parts, and can therefore obtain complete information about the contour of the object. The device operates without making any conventional images, and is therefore much faster than comparable devices of the prior art. Also, the laser and beam deflector can be housed in a small optical head which enables the device to reach normally inaccessible areas. The device can compare the test object with a reference object, or it can compare two objects for differences.

Hooker, Jeffery A.↗

DOE OSTI2020

Stability of zirconium hydride

This reports complete Milestone M2.2.1 Stability of zirconium hydride: Experimental investigation of the hydrogen concentration of encapsulated zirconium hydride before and after joining. In this milestone, we first report the successful fabrication of crack-free bulk zirconium hydride by using the ORNL static hydriding system. The fabricated hydride was characterized by using X-ray diffraction (XRD) and X-ray computed tomography (XCT). XRD results showed that the δ-phase zirconium hydride, α-zirconium, and ε-phase hydride were present. XCT confirmed the absence of the internal cracking. The hydrogen concentration was determined by the weight change before and after hydrogen loading, given the fact that the oxide phase was not found during XRD analysis. Two metallic cladding materials, i.e., molybdenum and FeCrAl, were selected to encapsulate the fabricated zirconium hydride pellets. Demonstration capsules were designed and machined. Mo crucible was successfully sealed by using a combination of electron beam welding and gas tungsten arc welding. Due to the undesired neutronics property of Mo, further investigation of this cladding material was not pursued. Electron beam welding and laser beam welding were employed to seal the FeCrAl capsules. XRD were performed on the zirconium hydride before and after the sealing. The results showed that the welding process has negligible impact on the hydrogen content in the FeCrAl-canned zirconium hydride. The presented work fulfilled the proposed work under this milestone and paves a pathway to fabricate single-phase zirconium hydride and to develop robust cladding materials to can bulk zirconium hydride.

36 MATERIALS SCIENCE↗

NASA NTRS1986

Recording Interferograms Holographically

Images of experiments stored for later analysis Classical interferometer modified for holography by removing entrance semireflecting mirror and inserting holographic recording in one of legs. Collimated laser beam projected through hologram and directed to remaining semitransparent mirror. Combines with reference beam from same laser to form virtual image of original experiment. Developed for experiments on crystal growth during space flights. Images recorded rapidly under constraints of experiments and later examined on ground.

Comeens, E. R.↗

NASA NTRS1986

Program for Heat Flow in Welding

Program contains numerical model of temperature distribution in vicinity of weld. Weld model used to produce estimated welding power requirements, welding-power-loss analysis, heat-affected-zone temperature history, and weld-puddle cross-section plots. Applied to gas/tungsten-arc, plasma-arc, electron-beam, and laser-beam welds on wide plates under steady conditions. User predicts power requirements and temperature distributions. Weld model written in BASIC.

Nunes, A. C., Jr.↗

NASA NTRS1985

Wavelength error analysis in a multiple-beam Fizeau laser wavemeter having a linear diode array readout

An estimate of the wavelength accuracy of a laser wavemeter is performed for a system consisting of a multiple-beam Fizeau interferometer and a linear photosensor array readout. The analysis consists of determining the fringe position errors which result when various noise sources are included in the fringe forming and detection process. Two methods of estimating the fringe centers are considered: (1) maximum pixel current location, and (2) average pixel location for two detectors with nearly equal output currents. Wavelength error results for these two methods are compared for some typical wavemeter parameters.

Robinson, D. M.↗