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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 NTRS1991

Efficient second-harmonic conversion of CW single-frequency Nd:YAG laser light by frequency locking to a monolithic ring frequency doubler

Efficient second-harmonic conversion of the 1064-nm output of a diode-pumped CW single-frequency Nd:YAG laser to 532 nm was obtained by frequency locking the laser to a monolithic ring resonator constructed of magnesium-oxide-doped lithium niobate. The conversion efficiency from the fundamental to the second harmonic was 65 percent. Two hundred milliwatts of CW single-frequency 532-nm light were produced from 310 mW of power of 1064-nm light. This represents a conversion efficiency of 20 percent from the 1-W diode laser used to pump the Nd:YAG laser to single-frequency 532-nm output. No signs of degradation were observed for over 500 h of operation.

Gerstenberger, D. C.↗
NASA NTRS1991

Multiphoton ionization of N2 by the third harmonic of a Nd:YAG laser - A new avenue for air diagnostics

Laser-induced N2 ionization is accomplished using a commercially available Nd:YAG laser, and confirmed by means of ion-collection and spectral measurements. Neutral N2 is excited by six photons of the third harmonic frequency, or 355 nm, and is transformed to an ionized state. The radiation at 355 nm is separated from the fundamental and frequency-doubled Nd:YAG radiation to guarantee monochromatic incident radiation. Intense lines near 391.4 nm are found in the initial laser polarization and for a 90-degree rotation of polarization. The radiation at 391.4 nm is associated with an incoherent laser-induced flourescence process related to an ionized-state transition, and increases quadratically with laser power. A 45-mJ laser pulse focused to a diameter of 17 microns can produce an ion concentration of 3.25 x 10 to the 13th ions/cu cm. The large ion concentration and robust fluorescence signal make this technique an efficient method for time-of-flight velocimetry and in-flight testing.

Laufer, Gabriel↗
NASA NTRS1992

Two-Pass, Diode-Pumped Nd:YAG Slab Laser Head

Neodymium/yttrium aluminum garnet (Nd:YAG) ring-laser head designed for compactness, simplicity, and increased efficiency for side pumping by diode lasers. Laser head includes two linear arrays of diode lasers, two fused-silica collimating rods, and Nd:YAG slab. Slab mounted on finned copper block, providing good thermal dissipation.

Coyle, D. Barry↗
NASA NTRS1992

Post flight operation of a high peak power neodymium YAG laser aboard the G-449 payload flown on Space Shuttle Columbia mission 61-C

The Nd Yag laser flown on board the G-449 payload completed its postflight testing successfully. There was no indication that the laser had undergone any electronic or optical component failure. A postflight video was taken immediately following the return of the payload to the laboratory. Early anticipation of vibration and temperature changes contributed to the successful operation of the laser. Photographic material resulting from post flight videotape are presented. NASA safety reviews and recommendations supplied the insights which helped contribute to the successful operation of the Nd Yag laser. The safety review data is part of the technical presentation and gives some insight into why the system survived the severe environment of temperature and vibration during the flight of Space Shuttle 61-C.

Muckerheide, M. C.↗
NASA NTRS1993

Development of a 100 mJ, 5 Hz, flashlamp-pumped, Cr,Tm:YAG coherent lidar transmitter

A contract to develop a 100 mJ, 5 Hz, flashlamp-pumped Cr,Tm:YAG coherent lidar transmitter has been awarded to Coherent Technologies, Inc. (CTI). The lidar transmitter will operate at an eyesafe wavelength of 2.01 microns. The development complements work being performed under an SBIR Phase II with Electro-Optics Technology (EOT). EOT is developing continuous wave, low and medium power Tm:YAG oscillators of a unique design. One of the low power oscillators will be used as the injection seeder/local oscillator in the CIT lidar transmitter. The lidar transmitter will require the addition of a receiver section. Once completed, the lidar will be used in atmospheric performance studies, allowing comparison with that of the more mature CO2 lidar technology. The focus of current research and plans for next year are presented.

Henderson, S.↗
NASA NTRS1992

Injection seeded, diode pumped regenerative ring Nd:YAG amplifier for spaceborne laser ranging technology development

A small, all solid state, regenerative ring amplifier designed as a prototype for space application is discussed. Novel features include dual side pumping of the Nd:YAG crystal and a triangular ring cavity design which minimizes the number of optical components and losses. The amplifier is relatively small (3 ns round trip time) even though standard optical elements are employed. The ring regeneratively amplifies a 100 ps single pulse by approximately 10(exp 5) at a repetition rate of 10 to 100 Hz. The amplifier is designed to be injection seeded with a pulsed, 100 ps laser diode at 1.06 microns, but another Nd:YAG laser system supplying higher pulse energies was employed for laboratory experiment. This system is a prototype laser oscillator for the Geoscience Laser Ranging System (GLRS) platform. Results on measurements of beam quality, astigmatism, and gain are given.

Coyle, D. Barry↗
NASA NTRS1992

Characterization of a Nd:YAG doubled pulsed laser system

A description of a frequency doubled, double pulsed Nd:YAG laser that is to be used to pump an injection locked Ti:Sapphire power oscillator is presented. These two lasers make up the transmitter portion of the Lidar Atmospheric Sensing Experiment (LAWSE) instrument. LASE is a Lidar/DIAL experiment that is to measure water vapor in the troposphere. By utilizing the twin concept, both pulses can be produced with a single laser system, thereby minimizing cost, size, and weight. Alignment problems associated with having two separate lasers each produce one of the twin pulses are also alleviated. The LASE transmitter consists of a doubled pulsed Nd:YAG laser that will pump a Ti:Sapphire power oscillator that will be injection-locked by a diode laser. The wavelength of the Ti:Sapphire output will be tunable from 813 to 818 nm. A performance summary of the pump laser is given. The data verify that the pump laser can meet the performance requirements to pump the Ti:Sapphire power oscillator.

Williams-Byrd, Julie A.↗
NASA NTRS1992

Diode pumped, regenerative Nd:YAG ring amplifier for space application

The study reviews the research and development of a prototype laser used to study one possible method of short-pulse production and amplification, in particular, a pulsed Nd:YAG ring laser pumped by laser diode arrays and injected seeded by a 100-ps source. The diode array pumped, regenerative amplifier consists of only five optical elements, two mirrors, one thin film polarizer, one Nd:YAG crystal, and one pockels cell. The pockels cell performed both as a Q-switch and a cavity dumper for amplified pulse ejection through the thin film polarizer. The total optical efficiency was low principally due to the low gain provided by the 2-bar pumped laser head. After comparison with a computer model, a real seed threshold of about 10 exp -15 J was achieved because only about 0.1 percent of the injected energy mode-matched with the ring.

Coyle, D. B.↗
NASA NTRS1995

The Effect of Temperature on the Radiative Performance of Ho-Yag Thin Film Selective Emitters

We present the emitter efficiency results for the thin film 25 percent Ho YAG (Yttrium Aluminum Garnet, Y3Al5O12) selective emitter from 1000 to 1700 K with a platinum substrate. Spectral emittance and emissive power measurements were made (1.2 less than lambda less than 3.2 microns) and used to calculate the radiative efficiency. The radiative efficiency and power density of rare earth doped selective emitters are strongly dependent on temperature and experimental results indicate an optimum temperature (1650 K for Ho YAG) for thermophotovoltaic (TPV) applications.

Lowe, Roland A.↗
NASA NTRS1996

Nd:YAG Laser-Based Dual-Line Detection Rayleigh Scattering and Current Efforts on UV, Filtered Rayleigh Scattering

Ongoing research in Rayleigh scattering diagnostics for variable density low speed flow applications and for supersonic flow measurements are described. During the past several years, the focus has been on the development and use of a Nd:YAG-based Rayleigh scattering system with improved signal-to-noise characteristics and with applicability to complex, confined flows. This activity serves other research projects in the Aerodynamics Laboratory which require the non-contact, accurate, time-frozen measurement of gas density, pressure, and temperature (each separately), in a fairly wide dynamic range of each parameter. Recently, with the acquisition of a new seed-injected Nd:YAG laser, effort also has been directed to the development of a high-speed velocity probe based on a spectrally resolved Rayleigh scattering technique.

Otugen, M. Volkan↗
NASA NTRS1997

Improvement in Suppression of Pulsed Nd:YAG Laser Light With Iodine Absorption Cells for Filtered Rayleigh Scattering Measurements

Filtered Rayleigh scattering using iodine absorption cells is an effective technique for obtaining density, temperature, and velocity measurements in high speed confined flows. By tuning a single frequency laser to a strong iodine absorption line, stray scattered laser light can be greatly suppressed. For example, the minimum transmission predicted by an iodine absorption model calculation is less than 10(exp -5) at the 18788.44/cm line using a 200 mm absorption cell containing iodine vapor at 0.46 T. Measurements obtained by other researches using a CW Nd:YAG laser agree with the model calculations. However, measurements made by us and by others using Q-switched, injection-seeded, frequency doubled Nd:YAG lasers only show minimum transmission of about 3 x 10(exp -3). This greatly reduces the applicability of the filtered Rayleigh scattering technique using these lasers in experiments having large amounts of stray scattered laser light. The purposes of the present study are to characterize the spectrum of the excess light transmitted by the iodine cell and to make changes to the laser to reduce the transmitted laser light. Transmission data as a function of laser frequency for the iodine absorption line at 18788.44/cm are presented. A planar mirror Fabry-Perot interferometer was used to characterize the frequency spectrum of the light passed through the cell. Measurements taken with the laser tuned to the center of the iodine absorption line show the light transmitted through the iodine cell to have a component with a bandwidth of about 40 GHz. This is probably caused by other modes in the laser that exist in spite of the single frequency injection beam. A second broadband component was also observed, possibly caused by the laser flash lamps or by fluorescence. An intracavity etalon was installed in the laser oscillator cavity to suppress the 40 GHz component. Measurements taken with the etalon tuned to the injection frequency showed a reduction in the transmitted laser light. This improvement allows the iodine cell to block significantly more of the stray laser light in filtered Rayleigh scattering experiments. Examples are given of filtered Rayleigh scattering measurements showing the effect of the etalon on measurements taken in a Mach 3 flow in the NASA Lewis 4 inch by 10 inch supersonic wind tunnel.

Seasholtz, Richard G.↗
NASA NTRS2005

4-Pass Pumping of Nd+3:YAG Slabs

A solid-state, side pumping scheme, designed to enhance pump energy absorption, has been adapted for use in small, side-pumped, Nd+3:YAG zigzag lasers. This technique allows for pump radiation to make four complete passes through the gain medium, effectively doubling the absorption length of the usual 2-pass geometry. This produces higher inversion densities, higher gains, broader operating temperature bands and overall higher efficiencies. The improved performance has been demonstrated with a small Nd+3:YAG, mJ-class oscillator, and will aid in the development for space-based remote sensing laser transmitters for altimetry and mapping instruments.

Coyle, D. Barry↗
NASA NTRS2008

Single-mode, All-Solid-State Nd:YAG Laser Pumped UV Converter

In this paper, the status of a high-energy, all solid-state Nd:YAG laser pumped nonlinear optics based UV converter development is discussed. The high-energy UV transmitter technology is being developed for ozone sensing applications from space based platforms using differential lidar technique. The goal is to generate greater than 200 mJ/pulse with 10-50 Hz PRF at wavelengths of 308 nm and 320 nm. A diode-pumped, all-solid-state and single longitudinal mode Nd:YAG laser designed to provide conductively cooled operation at 1064 nm has been built and tested. Currently, this pump laser provides an output pulse energy of >1 J/pulse at 50 Hz PRF and a pulsewidth of 22 ns with an electrical-to-optical system efficiency of greater than 7% and a M(sup 2) value of <2. The single frequency UV converter arrangement basically consists of an IR Optical Parametric Oscillator (OPO) and a Sum Frequency Generator (SFG) setups that are pumped by 532 nm wavelength obtained via Second Harmonic Generation (SHG). In this paper, the operation of an inter cavity SFG with CW laser seeding scheme generating 320 nm wavelength is presented. Efforts are underway to improve conversion efficiency of this mJ class UV converter by modifying the spatial beam profile of the pump laser.

Prasad, Narasimha S.↗
DOE OSTI2020

3D printed transparent ceramic YAG laser rods: Matching the core-clad refractive index

Yttrium Aluminum Garnet (YAG) solid state laser gain media rods with an active Neodymium-doped core and an optically-clear cladding region were additively manufactured via direct-ink-writing (DIW), followed by sintering and hot isostatic pressing to form fully dense optical ceramics. Lutetium and Gadolinium were chosen as optically-inert co-doping ions in the clad to match the increase in refractive index caused by the Neodymium in the core. Additionally, either 11.6% Lutetium or 3.8% Gadolinium can be used to match the index change from 2% neodymium; however, differences in diffusion distances across the core-clad interface lead to large fluctuations in index in that region. These index fluctuations can be minimized either by matching dopants with similar diffusion distances, or by implementing a gradual gradient in the doping profile, possible through DIW, rather than a sharp compositional interface attainable via more standard fabrication methods. This improvement in index homogeneity resulted in a 40% improvement in lasing performance compared with that of a core-clad rod fabricated with a sharp interface between the doped and undoped regions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on YAg by Materials Project

YAg is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Y is bonded in a body-centered cubic geometry to eight equivalent Ag atoms. All Y–Ag bond lengths are 3.16 Å. Ag is bonded in a body-centered cubic geometry to eight equivalent Y atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Laser and thermooptical characteristics of a laser head based on a thin Yb : YAG slab

Amplification and thermally induced phase distortions in a cw pumped laser head with an active element in the form of a thin Yb : YAG slab are experimentally studied. Lasing characteristics of an emitter based on this laser head are examined. Laser radiation is obtained with an average power of 32 W and a slope efficiency with respect to the absorbed pump power η = 68 %. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Relaxation oscillations in a bipolarised Nd : YAG laser with a Fabry – Perot cavity

Based on the model of a bipolarised laser, which takes into account real orientations of absorbing and emitting dipoles of active centres in the unit cell of an Nd : YAG single crystal, we have shown that the appearance of low-frequency relaxation oscillations requires the participation of both competing pump channels through linearly and circularly polarised dipole transitions. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗