Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “raman”

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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Measuring Hydrogen Plumes With Raman Lidar

Prototype Raman lidar system measures concentration of hydrogen gas in atmosphere as function of position, with range resolution of 3 ft over 3,000 ft. Sensitive to concentrations smaller than 0.5 percent, 10 times below minimum flammable concentration. Pulsed ultraviolet laser beam excites Raman emissions from molecules to be detected. Backscattered light collected by telescope, filtered at appropriate wavelengths, and sent to photodetectors. Developed for use as safety monitor, and to study dispersion of hydrogen gas leaking into atmosphere.

Caputo, Bernard↗
NASA NTRS1991

Laser Raman diagnostics in subsonic and supersonic turbulent jet diffusion flames

Ultraviolet (UV) spontaneous vibrational Raman scattering combined with laser-induced predissociative fluorescence (LIPF) is developed for temperature and multi-species concentration measurements. Simultaneous measurements of temperature, major species (H2, O2, N2, H2O), and minor species (OH) concentrations are made with a 'single' narrow band KrF excimer laser in subsonic and supersonic lifted turbulent hydrogen-air diffusion flames. The UV Raman system is calibrated with a flat-flame diffusion burner operated at several known equivalence ratios from fuel-lean to fuel-rich. Temperature measurements made by the ratio of Stokes/anti-Stokes signal and by the ideal gas law are compared. The single shot measurement precision for concentration and temperature measurement is 5 to 10 pct. Calibration constants and bandwidth factors are determined from the flat burner measurements and used in a data reduction program to arrive at temperature and species concentration measurements. These simultaneous measurements of temperature and multi-species concentrations allow a better understanding of the complex turbulence-chemistry interactions and provide information for the input and validation of CFD models.

Cheng, T. S.↗
NASA NTRS1992

An Extention of the Raman-lidar Technique to Measure the Velocity and Temperature of the Atmospheric Emission Jets from Stacks

If a Raman lidar possesses a proper spatial resolution sufficient for acquiring profiles of return signals across an emission jet, then the difference in number densities of nitrogen molecules within the jet and outside it will cause a dip in the lidar return signal from nitrogen. Experimentation showed that the Raman lidar technique can accurately measure the velocity and temperature of atmospheric emission from smoke stacks.

Arshinov, Yu. F.↗
NASA NTRS1992

Measurement of multiple scattering effects with a polarization Raman elastic-backscatter lidar

A new method for the determination of multiple scattering effects is described. A polarization Raman elastic backscatter lidar is used, which allows the measurement of the depolarization of both the elastically backscattered light and the light Raman scattered from nitrogen molecules. With this technique the depolarization effect due to multiple scattering can be separated from single scattering polarization. Presented here are a short discussion of the idea and a measurement example.

Wandinger, Ulla↗
NASA NTRS1991

Collisional broadening, line shifting, and line mixing in the stimulated Raman 2nu2 Q branch of CH4

Self-, argon-, and helium-broadening coefficients have been measured for 13 lines in the 2nu2 Raman Q branch of CH4 using stimulated inverse Raman spectroscopy. The linewidths clearly show the symmetry-state dependence characteristic of pressure broadening, and inelastic processes in general, involving spherical-top molecules. Pressure-induced line shifts have also been measured for these features in pure methane. The pressure-shift coefficients do not display the symmetry-state dependence found for the linewidths. By applying the Rosenkranz perturbation treatment to a pair of collisionally mixed lines, an estimate of individual state-to-state contributions to the overall linewidth has been obtained.

Millot, G.↗
NASA NTRS1992

Collisional broadening of rotational lines in the stimulated Raman pentad Q-branch of CD4

Self- and argon-broadening coefficients are reported for a number of Raman Q-branch transitions in the nu(1) and nu(2) + nu(4) bands of (C-12)D4 at room temperature (296 K). The coefficients display a variation with j and with C exp n (symmetry species A, E, F) that is essentially independent of collision partner and which is similar to the j- and C exp n-dependence found in previous measurements of the IR line-broadening coefficients. The rotationally inelastic collision rates previously measured by Foy et al. (1988) for (C-13)D4 (V4 = 0, 1) in collision with (C-13)D4 or Ar account for only a part of the Raman broadening rate, suggesting possibly significant contributions to the linewidths from efficient V-V transfer or elastic dephasing collisions.

Millot, G.↗
NASA NTRS1992

Raman scattering of InGaAs/InP grown by uniform radial flow epitaxy

Uniform radial flow epitaxy, a novel growth technique, has been used to grown InGaAs films on InP. Epitaxial layers above and below the critical thickness for the onset of slip were grown. Raman spectroscopy was used to characterize the quality of epitaxial layers, determine alloy composition, and measure the strain. Raman spectra from both pseudomorphic (strained) and relaxed (unstrained) InGaAs films were obtained at 300 and 80 K. The difference in the frequencies of their GaAs-like longitudinal optical phonons was used to calculate stress for the strained InGaAs/InP, leading to a direct formula for the evaluation of the layer stress.

Feng, Z. C.↗
NASA NTRS1992

Nonequilibrium vibrational population measurements in an expanding flow using spontaneous Raman scattering

Vibrational relaxation of nitrogen in a 2D nozzle flow is studied using spontaneous Raman scattering. An electric arc driven shock tube operating as a reflected shock tunnel produces stagnation conditions of 5600 K and 100 atm. A 248 nm KrF laser pulse is focused into the nozzle to produce spatially resolved spontaneous Raman spectra. Vibrational population distributions are derived from the spectra for the states v = 0 to v = 8. The experimental results are compared with two theoretical models: the Landau-Teller relaxation model and a numerical solution of the master equations using transition rates derived from SSH theory. The Landau-Teller correction factor has been measured at 1.0 - 1.5.

Sharma, Surendra P.↗
NASA NTRS1992

Raman lidar measurements of Pinatubo aerosols over southeastern Kansas during November-December 1991

Raman lidar measurements over southeastern Kansas of stratospheric aerosols produced by the June 1991 eruptions of Mt. Pinatubo were made on 10 nights during November and December 1991. Both aerosol backscattering and extinction profiles were derived simultaneously from the lidar data since this system detects Raman scattering from nitrogen and oxygen as well as the backscattered light from aerosols and molecules. Aerosols scattering ratios greater than 3(at 351 nm) were measured on several nights. Peak aerosol concentrations were located between 19-22 km and varied significantly from night to night. Aerosol extinction/backscatter ratios computed from the lidar data and averaged over the altitude region of enhanced aerosol scattering between 15-25 km varied between 18-28 sr. Mie computations show these values to be consistent with scattering by aerosol particles with mode radii between 0.3 to 0.5 micron and that the ratios would increase to 40-65 sr at 694 nm. Aerosol optical thicknesses derived from the lidar extinction measurements at 351 nm varied between 0.04 and 0.06.

Ferrare, R. A.↗
NASA NTRS1992

Raman spectra of seven interplanetary dust particles

The Raman shift spectra of seven interplanetary dust particles, U2034(F10), U2034(F8), U2022(B1), W7074 18, W7074 C15, W7074 C3 and W7074 A7, were measured with a Spex-1403 Raman spectrograph. The exciting radiations were the 488 nm and 514 nm line of a 5W argon ion laser. All seven spectra exhibit the 1350 and 1600 Delta/cm arbon bands, implying that the Interplanetary dust particles were coated with hydrocarbon and incompletely crystallized carbon, the part of which may be the residue of hydrocarbon contents in the particles after water loss by the heating during their entry into the earth's atmosphere. A weak band structure in the 520-610/cm range could be caused by cyclosilicates, and a weak band at 2900/cm is tentatively identified as due to hydrocarbon molecules.

Xu, Yin-Lin↗
NASA NTRS1993

Temperature sensitivity of an atmospheric Raman lidar system based on a XeF excimer laser

The temperature sensitivity of Raman backscattering from atmospheric nitrogen, oxygen, and water vapor is considered over the range of temperatures expected in the troposphere. These results are applied to the Raman spectrum induced by a XeF excimer laser, which produces three line groups centered at approximately 349, 351, and 353 nm. Bandpass filter characteristics are determined for this case.

Whiteman, David N.↗
NASA NTRS1994

Raman structural studies of the nickel electrode

The objectives of this investigation have been to define the structures of charged active mass, discharged active mass, and related precursor materials (alpha-phases), with the purpose of better understanding the chemical and electrochemical reactions, including failure mechanisms and cobalt incorporation, so that the nickel electrode may be improved. Although our primary tool has been Raman spectroscopy, the structural conclusions drawn from the Raman data have been supported and augmented by three other analysis methods: infrared spectroscopy, powder X-ray Diffraction (XRD), and x-ray absorption spectroscopy (in particular EXAFS, Extended X-ray Absorption Fine Structure spectroscopy).

Cornilsen, Bahne C.↗
NASA NTRS1994

Atomic oxygen fluorescence excitation using a Raman-shifted, tunable ArF-excimer laser

A novel method for exciting the two-photon, 2p3 3p 3P left arrow 2p4 3P atomic oxygen transition is reported. The transition to the upper state is achieved through the combined absorption of photons from the second and third Stokes order pulses of an ArF-excimer laser that is wavelength-shifted by the use of deuterium Raman cell. All three transitions from the ground electronic state of the oxygen atom lie within the tuning range of the Raman-shifted ArF laser. The available pulse energy from this laser configuration is comparable to that of commercially available Nd:YAG-pumped dye laser systems operated at 226 nm.

Fletcher, D. G.↗
NASA NTRS1994

Raman lidar profiling of atmospheric water vapor: Simultaneous measurements with two collocated systems

Raman lidar is a leading candidate for providing the detailed space- and time-resolved measurements of water vapor needed by a variety of atmospheric studies. Simultaneous measurements of atmospheric water vapor are described using two collocated Raman lidar systems. These lidar systems, developed at the NASA/Goddard Space Flight Center and Sandia National Laboratories, acquired approximately 12 hours of simultaneous water vapor data during three nights in November 1992 while the systems were collocated at the Goddard Space Flight Center. Although these lidar systems differ substantially in their design, measured water vapor profiles agreeed within 0.15 g/kg between altitudes of 1 and 5 km. Comparisons with coincident radiosondes showed all instruments agreed within 0.2 g/kg in this same altitude range. Both lidars also clearly showed the advection of water vapor in the middle troposphere and the pronounced increase in water vapor in the nocturnal boundary layer that occurred during one night.

Goldsmith, J. E. M.↗
NASA NTRS1995

Raman scattering characterization of space solar cell structures

A contactless method for the determination of the free-carrier density and the composition distribution across the thickness of 3-5 multi-layer solar cell structures, using the Raman scattering method, is developed. The method includes a step analysis of Raman spectra from optical phonons and phonon-plasmon modes of different layers. The method provides simultaneous measurements of the element composition and the thickness of the structure's layers together with the free-carrier density. The results of measurements of the free-carrier density composition distributions of the liquid phase epitaxy grown AlGaAs/GaAs and GaSb solar cell structures are presented and discussed.

Mintairov, Alexander M.↗
NASA NTRS1995

Flight results for the airborne Raman lidar

The airborne Raman lidar recently completed a series of flight tests aboard a C-130 aircraft operated by the NASA Wallops Flight Facility. The Raman lidar is intended to make simultaneous remote measurements of methane, water vapor, temperature, and pressure. The principal purpose of the measurements is to aid in the investigation of polar phenomena related to the formation of ozone 'holes' by permitting the identification of the origin of air parcels using methane as a tracer.

Heaps, William S.↗
NASA NTRS1998

Raman Lidar Measurements of Aerosol Extinction and Backscattering: Methods and Comparisons - Report 1

This paper examines the aerosol backscattering and extinction profiles measured at night by the NASA Goddard Space Flight Center Scanning Raman Lidar (SRL) during the remote cloud sensing (RCS) intensive operations period (IOP) at the Department of Energy Atmospheric Radiation Measurement (ARM) southern Great Plains (SGP) site in April 1994. These lidar data are used to derive aerosol profiles for altitudes between 0.0 1 5 and 5 km. Since this lidar detects Raman scattering from nitrogen and oxygen molecules as well as the elastic scattering from molecules and aerosols, it measures both aerosol backscattering and extinction simultaneously. The aerosol extinction/backscattering ratio varied between approximately 30 sr and 75 sr at 351 nm. Aerosol optical thicknesses derived by integrating the lidar profiles of aerosol extinction measured at night between 0. I and 5 km are found to be about 10-40% lower than those measured by a Sun photometer during the day. This difference is attributed to the contribution by stratospheric aerosols not included in the lidar estimates as well as to diurnal differences in aerosol properties and concentrations. Aerosol profiles close to the surface were acquired by pointing the lidar nearly horizontally. Measurements of aerosol scattering from a tower-mounted nephelometer are found to be 40% lower than lidar measurements of aerosol extinction over a wide range of relative humidities even after accounting for the difference in wavelengths. The reasons for this difference are not clear but may be due to the inability of the nephelometer to accurately measure scattering by large particles.

Ferrare, R. A.↗
NASA NTRS1999

In Site Analysis of a High Temperature Cure Reaction in Real Time Using Modulated Fiber-Optic FT-Raman Spectroscopy

The vibrational spectrum of a high temperature (330 C) polymerization reaction was successfully monitored in real time using a modulated fiber-optic FT-Raman spectrometer. A phenylethynyl terminated monomer was cured, and spectral evidence for two different reaction products was acquired. The products are a conjugated polyene chain and a cyclized trimer. This is the first report describing the use of FT-Raman spectroscopy to monitor a high temperature (greater than 250 C) reaction in real time.

Cooper, John↗