Search NASA⌕ Search

SEARCH · Search NASA

Results for “laser operating parameters”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Kinetic study of terahertz generation based on the interaction of two-color ultra-short laser pulses with molecular hydrogen gas

In this work, using a two dimensional particle in cell-Monte Carlo collision simulation scheme, interaction of two-color ultra-short laser pulses with the molecular hydrogen gas (H{sub 2}) is examined. The operational laser parameters, i.e., its pulse shape, duration, and waist, are changed and, their effects on the density and kinetic energy of generated electrons, THz electric field, intensity, and spectrum are studied. It is seen that the best pulse shape generating the THz signal radiation with the highest intensity is a trapezoidal pulse, and the intensity of generated THz radiation is increased at the higher pulse durations and waists. For all the operational laser parameters, the maximum value of emitted THz signal frequency always remains lower than 5 THz. The intensity of applied laser pulses is taken about 10{sup 14} w/cm{sup 2}, and it is observed that while a small portion of the gaseous media gets ionized, the radiated THz signal is significant.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Numerical study for prediction of optimum operational parameters in laser welding of NiTi alloy

Laser welding of NiTi alloy is a challenging process since it strongly affects the functionality of the material in the heat affected and fusion zones. Furthermore, the inherent thermal process can remarkably change the transformation temperature of NiTi alloy in the welding zone because of variation in the material composition. Accordingly, the laser parameters such as laser power and velocity effectively determine the quality of the welded component. The functional and mechanical behavior of the resulting welded NiTi parts can also be effectively improved by controlling laser parameters, and consequently, improve the weldability quality. The purpose of the present study was to establish a reliable finite element model to predict the thermal behavior induced by the laser welding process. Here, a numerical model was employed to estimate the optimum laser parameters, which can reduce the heat affected and the fusion regions and thus result in a better weld. The results of the finite element model show good accuracy compared to the experimental results including the transient temperature and the dimension of the heat affected and fusion zones. In addition, an Artificial Neural Network (ANN) approach was applied, as a predictable tool, to perform a nonlinear mapping between inputs and outputs of the welding process in order to find the optimum laser parameters.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Meteorological effects on laser propagation for power transmission

An examination of possible laser operating parameters for power transmission to earth from solar power satellites is presented, with particular attention paid to assuring optimal delivery at midlatitudes. The degradation of beam efficiency due to molecular scattering, molecular absorption, aerosol scattering, and aerosol absorption during beam propagation through the atmosphere can be alleviated by judicious choice of wavelength windows, elevating the receptor sites, using a vertical propagation path, or by hole boring, i.e., vaporizing the aerosol particles in the beam path. Analyses are given for the beam propagation through fog, haze, clouds, and snow using various transitions. Only weapons-quality lasers are seen as being capable of boring through clouds and aerosols, employing a CW beam with superimposed pulses at high power densities. It is concluded that further short wavelength transmission experiments be performed to demonstrate transmission feasibility with the CW/pulsed mode of beam propagation.

Beverly, R. E., III↗
NASA NTRS1980

Satellite Power System (SPS) laser studies. Volume 2: Meteorological effects on laser beam propagation and direct solar pumped lasers for the SPS

The primary emphasis of this research activity was to investigate the effect of the environment on laser power transmission/reception from space to ground. Potential mitigation techniques to minimize the environment effect by a judicious choice of laser operating parameters was investigated. Using these techniques, the availability of power at selected sites was determined using statistical meteorological data for each site.

Beverly, R. E., III↗
NASA NTRSDate not supplied

Characterization Progress of an Absorption Laser Differential Interferometer

An absorption laser differential interferometer (A-LDI) system can be used to provide simultaneous, colinear measurements of flow properties (pressure, temperature, concentration, velocity) and flow fluctuations. Further characterization work on the absorption aspect of the system is provided in this paper, including characterization of the laser operating parameters, comparisons of two etalons of different free spectral range, and the further evaluation of a fixed-wavelength absorption measurement that can be used to obtain absorption and LDI measurements with the same sampling rate. A 0.4 GHz etalon was demonstrated to provide sufficient fringe peaks at low modulation depths to be used for the low-pressure testing characteristic of hypersonic wind tunnel facilities. The use of a 3 GHz etalon as a low-cost relative wavemeter was tested and validated. Data taken with the fixed-wavelength strategy in a sub-atmospheric test cell using 100% O2was successful and will allow absorption and LDI data to be acquired simultaneously, colinearly, and at the same sampling rate, yielding a truly simultaneous measurement of the flow density fluctuations and the flow mean density.

Joshua M Weisberger↗
NASA NTRSDate not supplied

Characterization Progress of an Absorption Laser Differential Interferometer

An absorption laser differential interferometer (A-LDI) system can be used to provide simultaneous, colinear measurements of flow properties (pressure, temperature, concentration, velocity) and flow fluctuations. Further characterization work on the absorption aspect of the system is provided in this paper, including characterization of the laser operating parameters, comparisons of two etalons of different free spectral range, and the further evaluation of a fixed-wavelength absorption measurement that can be used to obtain absorption and LDI measurements with the same sampling rate. A 0.4 GHz etalon was demonstrated to provide sufficient fringe peaks at low modulation depths to be used for the low-pressure testing characteristic of hypersonic wind tunnel facilities. The use of a 3 GHz etalon as a low-cost relative wavemeter was tested and validated. Data taken with the fixed-wavelength strategy in a sub-atmospheric test cell using 100% O 2 was successful and will allow absorption and LDI data to be acquired simultaneously, colinearly, and at the same sampling rate, yielding a truly simultaneous measurement of the flow density fluctuations and the flow mean density.

Joshua M. Weisberger↗
NASA NTRS1981

Iodine monofluoride 140-kW laser - Small signal gain and operating parameters

Output energies in excess of 4 mJ in a 30-nsec FWHM pulse (140-kW peak power) have been obtained from a discharge-pumped IF laser for a cavity output coupling of 35%. In addition, oscillation on a new transition of the IF (E-A) band at 472.7 nm has been observed. By measurement of the output power of the laser for various values of output mirror transmission, the small signal gain and loss coefficients were found to be (3.1 + or - 0.7)%/cm and 0.3%/cm, respectively.

Dlabal, M. L.↗
DOE OSTI2016

Pulsed inductive HF laser

We report the results of experimentally investigated dependences of temporal, spectral and spatial characteristics of an inductive HF-laser generation on the pump conditions. Gas mixtures H{sub 2} – F{sub 2}(NF{sub 3} or SF6{sub 6}) and He(Ne) – H{sub 2} – F{sub 2}(NF{sub 3} or SF{sub 6}) were used as active media. The FWHM pulse duration reached 0.42 μs. This value corresponded to a pulsed power of 45 kW. For the first time, the emission spectrum of an inductive HF laser was investigated, which consisted of seven groups of bands with centres around the wavelengths of 2732, 2736, 2739, 2835, 2837, 2893 and 2913 nm. The cross section profile of the laser beam was a ring with a diameter of about 20 mm and width of about 5 mm. Parameters of laser operation in the repetitively pulsed regime were sufficiently stable. The amplitude instability of light pulses was no greater than 5% – 6%. (lasers)

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2012

LightForce: An Update on Orbital Collision Avoidance Using Photon Pressure

We present an update on our research on collision avoidance using photon-pressure induced by ground-based lasers. In the past, we have shown the general feasibility of employing small orbit perturbations, induced by photon pressure from ground-based laser illumination, for collision avoidance in space. Possible applications would be protecting space assets from impacts with debris and stabilizing the orbital debris environment. Focusing on collision avoidance rather than de-orbit, the scheme avoids some of the security and liability implications of active debris removal, and requires less sophisticated hardware than laser ablation. In earlier research we concluded that one ground based system consisting of a 10 kW class laser, directed by a 1.5 m telescope with adaptive optics, could avoid a significant fraction of debris-debris collisions in low Earth orbit. This paper describes our recent efforts, which include refining our original analysis, employing higher fidelity simulations and performing experimental tracking tests. We investigate the efficacy of one or more laser ground stations for debris-debris collision avoidance and satellite protection using simulations to investigate multiple case studies. The approach includes modeling of laser beam propagation through the atmosphere, the debris environment (including actual trajectories and physical parameters), laser facility operations, and simulations of the resulting photon pressure. We also present the results of experimental laser debris tracking tests. These tests track potential targets of a first technical demonstration and quantify the achievable tracking performance.

Stupl, Jan↗
NASA NTRS1982

Investigations of laser pumped gas cell atomic frequency standard

The performance characteristics of a rubidium gas cell atomic frequency standard might be improved by replacing the standard rubidium discharge lamp with a single mode laser diode. Aspects of the laser pumped gas cell atomic clock studied include effects due to laser intensity, laser detuning, and the choice of the particular atomic absorption line. Results indicate that the performance of the gas cell clock may be improved by judicious choice of the operating parameters of the laser diode. The laser diode also proved to be a valuable tool in investigating the operation of the conventional gas cell clock. Results concerning linewidths, the light shift effect and the effect of isotopic spin exchange in the conventional gas cell clock are reported.

Volk, C. H.↗
NASA NTRS2010

Widely Tunable Mode-Hop-Free External-Cavity Quantum Cascade Laser

The external-cavity quantum cascade laser (EC-QCL) system is based on an optical configuration of the Littrow type. It is a room-temperature, continuous wave, widely tunable, mode-hop-free, mid-infrared, EC-QCL spectroscopic source. It has a single-mode tuning range of 155 cm(exp -1) (approximately equal to 8% of the center wavelength) with a maximum power of 11.1 mW and 182 cm(exp -1) (approximately equal to 15% of the center wavelength), and a maximum power of 50 mW as demonstrated for 5.3 micron and 8.4 micron EC-QCLs, respectively. This technology is particularly suitable for high-resolution spectroscopic applications, multi-species tracegas detection, and spectroscopic measurements of broadband absorbers. Wavelength tuning of EC-QCL spectroscopic source can be implemented by varying three independent parameters of the laser: (1) the optical length of the gain medium (which, in this case, is equivalent to QCL injection current modulation), (2) the length of the EC (which can be independently varied in the Rice EC-QCL setup), and (3) the angle of beam incidence at the diffraction grating (frequency tuning related directly to angular dispersion of the grating). All three mechanisms of frequency tuning have been demonstrated and are required to obtain a true mode-hop-free laser frequency tuning. The precise frequency tuning characteristics of the EC-QCL output have been characterized using a variety of diagnostic tools available at Rice University (e.g., a monochromator, FTIR spectrometer, and a Fabry-Perot spectrometer). Spectroscopic results were compared with available databases (such as HITRAN, PNNL, EPA, and NIST). These enable precision verification of complete spectral parameters of the EC-QCL, such as wavelength, tuning range, tuning characteristics, and line width. The output power of the EC-QCL is determined by the performance of the QC laser chip, its operating conditions, and parameters of the QC laser cavity such as mirror reflectivity or intracavity losses. In order to maximize the output power, an analysis and optimization of the EC laser parameters has been performed. The parameters of the beam emitted from the gain medium, such as divergence angle, beam profile, and astigmatism, have been investigated. The gain medium has been fully characterized before and after each stage of modification. The main modification steps are coating one facet of the gain chip with a high reflectivity mirror and the other facet with an anti-reflection layer. Then the chip is mounted in the EC-QCL. The optomechanical design has been reviewed and improved to provide for precise collimation of the strongly divergent beam of the QCL and the tuning diffraction grating.

Wysocki, Gerard↗
NASA NTRS2017

Spectral and Radiometric Calibration Using Tunable Lasers

A tunable laser system includes a tunable laser, an adjustable laser cavity for producing one or more modes of laser light emitted from the tunable laser, a first optical parametric oscillator positioned in a light path of the adjustable laser cavity, and a controller operable to simultaneously control parameters of at least the tunable laser, the first optical parametric oscillator, and the adjustable laser cavity to produce a range of wavelengths emitted from the tunable laser system. A method of operating a tunable laser system includes using a controller to simultaneously control parameters of a tunable laser, an adjustable laser cavity for producing one or more modes of laser light emitted from the tunable laser, and a first optical parametric oscillator positioned in a light path of the adjustable laser cavity, to produce a range of wavelengths emitted from the tunable laser system.

McCorkel, Joel↗
DOE OSTI2015

On the possibility of a new passively Q-switched laser operation mode with periodic wavelength switching

The possibility of cw-pumped passively Q-switched laser operation has been examined theoretically. Also, we have proposed laser operation mode in which the output wavelength automatically switches between two values without any changes in cavity parameters. Using numerical simulation and an Er:YAG laser with a Co:ZnSe passive Q-switch as an example, we have found parameters that ensure such operation mode. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1991

Spatiospectral and picosecond spatiotemporal properties of a broad area operating channeled-substrate-planar laser array

Spatiospectral and spatiotemporal properties of an eight-element channeled-substrate-planar laser array are investigated in both CW and pulsed operating conditions. The closely spaced CSP array with strong optical coupling between array elements is characterized by a broad area laserlike operation determined by its spatial mode spectra. The spatiotemporal evolution of the near and far field exhibits complex dynamic behavior in the picosecond to nanosecond domain. Operating parameters for the laser device have been experimentally determined. These results provide important information for the evaluation of the dynamic behavior of coherent semiconductor laser arrays.

Yu, NU↗
DOE OSTI2018

Raman spectroscopy of oxygen carrier particles in harsh environments

Fossil fuel combustion processes generate CO2, a greenhouse gas of considerable concern. To reduce this emission, the National Energy Technology Laboratory (NETL) is evaluating alternative combustion approaches, including chemical looping combustion (CLC). This technique generates relatively pure CO2, suitable for subsequent capture and storage. CLC uses oxygen-carrier particles (OCPs) such as iron oxides, copper oxides, calcium sulfates, etc. to provide oxygen for the combustion process. Optimization of the overall combustion process requires knowledge of the oxidation state (e.g., content of Fe2O3 vs. Fe3O4) of the OCPs during the different stages of the CLC process. Unfortunately, the ability to make on-line measurements of the oxidation state of OCPs in harsh environments is lacking and new sensors need to be developed. We are evaluating non-contact, stand-off Raman spectroscopy to determine the relative concentrations of the oxidized and reduced forms of OCPs at temperatures between 800 °C and 1000 °C, and pressures of about 10 atm. Using cw and pulsed Raman spectroscopy, in combination with a pressurized high-temperature sample chamber, we have optimized the operating parameters such as laser wavelength, laser intensity, collection optic design, focal spot size, etc. and measured Raman spectra of various OCP materials at high temperatures. To extract from the Raman spectra relevant information such as the concentration ratio of a material in different oxidation states, the measured data needs to be processed, and statistical modeling and multivariate calibration need to be performed.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2017

Raman Spectroscopy for the On Line Analysis of Oxidation States of Oxygen Carrier Particles

The need for cleaner energy systems, including CO 2 capture technologies, is driving the current development of new combustion approaches such as chemical looping combustion (CLC). This process is based on using oxygen carrier particles (OCPs) such as iron oxides, copper oxides, calcium sulfates, etc. to provide the oxygen for the combustion process. In order to optimize the overall process performance, it is critical that the properties of the oxygen carriers are well-defined and maintained for their specific purpose during the different stages of the CLC process. One of the critical properties of the oxygen carrier is its oxidation state (e.g., content of Fe 2 O 3 vs. Fe 3 O 4 ) as it affects the fundamental operation of the CLC process. Unfortunately, the ability to make on-line measurements of the oxidation state of oxygen carriers is lacking and new sensors need to be developed. Our goal is to develop a sensor for the on-line analysis of the oxidation state of oxygen carrier particles and to demonstrate its feasibility. Oxygen carrier particles (OCPs) of interest include iron oxides, copper oxides, and calcium sulfate, with particle sizes typically less than 0.5 mm diameter. The expected operating conditions of the sensor include OCP temperatures in the range of 800 °C to 1000 °C, and pressures of about 10 atm. The expected results are to be of a statistical nature, providing relative concentrations of the different oxidation states. These requirements make a strong case for using non-contact, stand-off, pulsed Raman spectroscopy as a sensor for the high-temperature on-line analysis of oxygen carrier particles. In order to achieve our goal, we have set up and tested a pulsed Raman spectroscopy system in combination with a pressurized high-temperature sample chamber, and have taking initial Raman spectra of various materials at high temperature. We are now in the process of optimizing the operating parameters such as laser wavelength, laser intensity, collection optic design, focal spot size, data acquisition, etc. We will also develop an analysis procedure for the interpretation of the Raman spectra. Typical Raman spectra consist of a convolution of background signal and multiple individual spectra. In order to extract relevant information such as the concentration ratio of a material in different oxidation states, we need to process (background subtraction, deconvolution, fitting, etc.) the measured data. In addition, statistical modeling and multivariate calibration need to be performed to correctly analyze the Raman spectra.

20 FOSSIL-FUELED POWER PLANTS↗