Search NASA⌕ Search

SEARCH · Search NASA

Results for “Doppler-broadening”

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.

35 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Excitation of the OI (3s 5S0-3p 5P; lambda 7774 A) multiplet by electron impact on O2

Electron impact on O2 has been employed to ascertain the absolute cross-section value and emission linewidths of the OI (3s 5S0-3p 5P; 7774 A) multiplet. The emission linewidths are highly Doppler-broadened in dissociative excitation, and display two distinct kinetic energy distributions: which indicate that both purely repulsive and discrete, bound, excited molecular states, which then predissociate, are involved in the dissociation process that leads to the excitation of OI 7774 A. The magnitude of the measured cross-section and the fragment kinetic energy distribution both indicate that the previous time-of-flight studies of the metastable OI (5S0) state require reinterpretation.

Erdman, P. W.↗
NASA NTRS1987

Experimental and theoretical investigations of the optogalvanic effect in a Hg-Ar discharge

The optogalvanic effect induced in a Hg-Ar discharge by light at 546.1 nm is studied experimentally and theoretically. The plasma and its response to a disturbance in the atomic-level populations are described entirely in terms of electron collision cross sections and other fundamental parameters. In a detailed description of the laser interaction with the atomic system, it was necessary to take into account velocity-changing collisions (VCC). These collisions (VCC) strongly modify the interaction between the Doppler-broadened system and the optical field. In some Doppler-free optogalvanic spectra the dramatic influence of VCC on the velocity distribution of atomic-level population is evident. Measurements of the magnitude of the optogalvanic signal confirm most of the theoretical results. Some anomalous features of the impedance change due to a weak beam were observed when a strong counterpropagating beam was introduced.

Richardson, W. H.↗
NASA NTRS1988

Evidence for a common high-temperature superconducting effect in La(1.85)Sr(0.15)CuO4 and YBa2Cu3O7

The paper reports the positron-annihilation lifetime and Doppler-broadening energy spectra in La(1.85)Sr(0.15)CuO4 superconductors for T = 10-297 K. A strong temperature dependence in positron lifetime and momentum distribution parameters is observed for positron-electron annihilation data while the sample is in the superconducting state, but not while it is in the normal state. Experimental evidence is presented that the superconducting mechanisms in La(1.85)Sr(0.15)CuO4 and YBa2Cu3O7 are similar and it is suggested that this is a consequence of a common physics involving the delicate balance between localized- and itinerant-electron behavior.

Jean, Y. C.↗
NASA NTRS1989

Nonthermal synchrotron radiation and pair annihilation in gamma-ray bursts

A self-consistent Monte Carlo simulation of quantized synchrotron emission, pair production, and pair annihilation in strong (2 x 10 to the 12th G or greater) magnetic fields is presented as a model of the production of annihilation lines in gamma-ray burst sources. The calculation determines the self-consistent photon spectrum and pair distribution functions resulting from a nonthermal injection of electrons into a region of homogeneous, strong magnetic field. The results indicate that the appearance of observable annihilation features in gamma-ray burst spectra requires isotropic or fan-beamed injection of electrons with energies of at least 5 MeV. The lines are narrow because higher energy electrons escape annihilation and do not contribute to Doppler-broadening. Injection beamed along the field did not produce observable annihilation lines in any of the cases studied. As a result, emission at energies much greater than 1 MeV produced through beaming seems to be incompatible with observable annihilation in this model. These results are discussed in relation to observed features in gamma-ray burst spectra.

Preece, Robert↗
NASA NTRS1991

Discovery of a Doppler-limited CO line in the upper mesosphere of Venus - A new dynamical probe

The presence of CO in the upper atmosphere of Venus is a consequence of the photochemistry of CO2, the dominant atmospheric constituent. In December 1989 the J = 1-2 transition of CO was observed at 230 GHz. In addition to the broad absorption line first reported by Kakar et al. (1976), a narrow absorption feature at the center of the line due to upper mesospheric CO, where the temperature profile starts to exhibit diurnal variation with altitude. The narrow feature is approximately 600 kHz wide and is predominantly Doppler-broadened. The Doppler core provides a new means of measuring wind velocities at these altitudes in the atmosphere of Venus. Detection of small Doppler shifts in the line core can in principle be used to measure winds with an accuracy of 10 m/s. Results are presently limited by the 17 kHz uncertainty in the measured rest frequency, corresponding to a systematic error in wind velocity up to 22 m/s, and the absence of laboratory measurements of the pressure shift in CO by CO2.

Buhl, David↗
NASA NTRS1991

Solar flare gamma-ray line profiles

Solar gamma-ray lines are produced through collisions of pairs of positive ions whose center of mass energies are above the relevant thresholds for excitation of gamma-ray emitting states. Because of the low density of the solar plasma, prompt gamma rays are emitted by recoiling ions before significant energy loss has occurred. Thus, the lines are expected to be Doppler-broadened to widths of the order of a hundred KeV. Gamma-ray lines resulting from proton and alpha-particle (He-4 ion) beams on carbon and oxygen targets in the laboratory exhibit complex profiles which change rapidly with the gamma-ray observation angle. Earlier work has been limited to modeling laboratory and solar flare gamma-ray profiles produced by proton excitation, but laboratory profiles of the carbon 4.44-MeV line and oxygen 6.13-MeV line from alpha excitation have now been successfully modeled. Solar flare gamma-ray line profiles of the carbon and oxygen lines from heavy ions in the ambient solar medium interacting with representative high-energy proton and alpha particle populations are presented.

Lang, F. L.↗
NASA NTRS1994

High-energy gamma-ray emission from solar flares: Constraining the accelerated proton spectrum

Using a multi-component model to describe the gamma-ray emission, we investigate the flares of December 16, 1988 and March 6, 1989 which exhibited unambiguous evidence of neutral pion decay. The observations are then combined with theoretical calculations of pion production to constrain the accelerated proton spectra. The detection of pi(sup 0) emission alone can indicate much about the energy distribution and spectral variation of the protons accelerated to pion producing energies. Here both the intensity and detailed spectral shape of the Doppler-broadened pi(sup 0) decay feature are used to determine the spectral form of the accelerated proton energy distribution. The Doppler width of this gamma-ray emission provides a unique diagnostic of the spectral shape at high energies, independent of any normalisation. To our knowledge, this is the first time that this diagnostic has been used to constrain the proton spectra. The form of the energetic proton distribution is found to be severely limited by the observed intensity and Doppler width of the pi(sup 0) decay emission, demonstrating effectively the diagnostic capabilities of the pi(sup 0) decay gamma-rays. The spectral index derived from the gamma-ray intensity is found to be much harder than that derived from the Doppler width. To reconcile this apparent discrepancy we investigate the effects of introducing a high-energy cut-off in the accelerated proton distribution. With cut-off energies of around 0.5-0.8 GeV and relatively hard spectra, the observed intensities and broadening can be reproduced with a single energetic proton distribution above the pion production threshold.

Alexander, David↗
NASA NTRS1994

Hubble Space Telescope Goddard high-resolution spectrograph H2 rotational spectra of Jupiter's aurora

We have observed the emission spectrum from Jupiter's north auroral atmosphere with 0.57 A spectral resolution over 1204-1241 A. Bright emissions have been detected from 50 deg to 60 deg latitude at locations consistent with 6 to 30 R (sub J) auroral ovals, with much fainter emissions away form the auroral ovals. The emission spectrum is well fitted by both laboratory spectra and theoretical models of optically thin electron excited H2, with added Doppler-broadened Lyman Alpha emission. The observed Lyman Alpha emission wings extend more than 1 A from line center and appear correlated in strength with the H2 brightness. Individual rotational lines in the H2 Werner band system are resolved, allowing a determination of the H2 rotational temperature at the altitude of the emission. We derive best-fit temperatures from 400-450 to 700-750 K, with the auroral emission layer temperature changing either across the auroral oval or over several days' time. These observations demonstrate for the first time the ability to measure the observed rapid H2 temperature variations across Jupiter's auroral atmosphere.

Clarke, John T.↗
NASA NTRS1995

High Spectral Resolution Lidar measurements of extinction and particle size in clouds

The spectral width of light backscattered from molecules is increased due to Doppler shifts caused by the thermal motion of the molecules. The thermal motion of aerosol and cloud particles is much slower and the backscatter spectrum is nearly unchanged. The University of Wiconsin High Spectral Resolution Lidar (RSRL) measures optical properties of the atmosphere by separating the Doppler-broadened molecular backscatter return from the unbroadened aerosol return. The molecular backscatter cross section can be calculated from the molecular density profile. Thus, observing the magnitude of the measured molecular signal relative to the computed profile allows unambiguous measurement of the atmospheric extinction profile. The ratio of the aerosol return to the molecular return along with the computed molecular cross section provides direct measurement of the aerosol backscatter cross section.

Eloranta, E. W.↗
NASA NTRS1996

High Spectral Resolution Lidar Measurements Using an I2 Absorption Filter

The University of Wisconsin high spectral resolution lidar (HSRL) measures optical properties of the atmosphere by separating the Doppler-broadened molecular backscatter return from the unbroadened aerosol return. The HSRL was modified to use an I2 absorption cell The modified HSRL transmitter uses a continuously pumped, Q-switched, injection seeded, frequency doubled Nd:YAG laser operating at a 4 kHz pulse repetition rate. This laser is tunable over a 124 GHz frequency range by temperature tuning the seed laser under computer control.

Eloranta, E. W.↗
NASA NTRS2001

Spectral Diagnostics for Early-Type Stars in Support of High-Resolution Satellite Observation

High-resolution X-ray spectra have recently been obtained using the Chandra X-ray Satellite Observatory for the two hot supergiant stars zeta Pup and delta Ori. The spectra show the presence of strong K-shell line emission from O, Ne, Mg, Si, and S, as well as strong L-shell line emission from Fe. Initial examination of the spectra indicates that the lines are significantly broader than what would be expected for a stationary plasma, and appear to be consistent with Doppler-broadened emission from hot plasma forming in shock-heated regions embedded in the wind (see Figure 1). Chandra has sufficient spectral resolution to study the velocity structure of isolated X-ray line profiles. Our analysis for zeta Pup has shown blue-shifted and skewed line profiles, providing the most direct evidence that the X-ray source is embedded in the stellar wind. The sensitivity of the He-like fir (forbidden-intercombination-resonance) lines to a strong UV radiation field is used to estimate the radial distances at which lines of O VII, Ne IX, Mg XI, Si XIII, and S XV originate.

MacFarlane, Joseph J.↗
NASA NTRS2002

Broadband Direct Detection Submillimeter Spectrometer with Multiplexed Superconducting Transition Edge Thermometer Bolometers

We present performance results based on the first astronomical use of multiplexed superconducting bolometers as direct detectors (i.e., with cold electrons) for spectroscopy. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer for the Caltech Submillimeter Observatory (CSO). FIBRE's detectors are superconducting transition edge sensor (TES) bolometers read out by a SQUID multiplexer. The Fabry-Perot uses a low resolution grating to order sort the incoming light. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing 5 orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering Delta lambda/lambda = 1/7 at a resolution of delta lambda/lambda = 1/1200 can be acquired. This spectral resolution is sufficient to resolve Doppler-broadened line emission from external galaxies. FIBRE has been operated in the 350 Am (850 GHz) band. These bands cover line emission from the important star formation tracers neutral carbon [CI] and carbon monoxide (CO).

Benford, D. J.↗
NASA NTRS2004

First Astronomical Use of Multiplexed Transition Edge Sensor Bolometers

We present performance results based on the first astronomical use of multiplexed superconducting bolometers. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer that achieved first light in June 2001 at the Caltech Submillimeter Observatory (CSO). FIBRE's detectors are superconducting transition edge sensor (TES) bolometers read out by a SQUID multiplexer. The Fabry-Perot uses a low resolution grating to order sort the incoming light. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing 5 orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering Delta lambda/lambda = 1/7 at a resolution of delta lambda/lambda approx. 1/1200 can be acquired. This spectral resolution is sufficient to resolve Doppler-broadened line emission from external galaxies. FIBRE operates in the 350 m and 450 m bands. These bands cover line emission from the important star formation tracers neutral carbon (CI) and carbon monoxide (CO). We have verified that the multiplexed bolometers are photon noise limited even with the low power present in moderate resolution spectrometry.

Staguhn, J. G.↗
NASA NTRS2003

Performance characteristics of narrow linewidth fiber laser pumped mid-IR difference frequency mixing light source for methane detection

A high-power, narrow-linewidth Yb fiber laser with a fiber Bragg grating (FBG) pumped difference frequency generation (DFG) in a periodically poled lithium niobate (PPLN) crystal was investigated in detail. A mid-IR power of approximately 2.3 microW at 3.3 micrometers with a slope efficiency of 0.85 mW/W2 was achieved. A Doppler-broadened absorption spectrum of CH4 at 3038.497 cm-1 (3.2911 micrometers) was obtained with a 0.1-m long-gas cell at a pressure of 133 Pa. The linewidth of the DFG source was evaluated to be less than 96 MHz from the observed spectral linewidth. Real-time monitoring of CH4 (approximately 1.78 ppm) in ambient air in a multipass cell which has an optical path length of 10 m was also demonstrated.

Non-NASA Center↗
NASA NTRS2001

Yb fiber laser pumped mid-IR source based on difference frequency generation and its application to ammonia detection

A Yb fiber laser pumped cw narrow-linewidth tunable mid-IR source based on a difference frequency generation (DFG) in a periodically poled LiNbO3 (PPLN) crystal for trace gas detection was demonstrated. A high power Yb fiber laser and a distributed feedback (DFB) laser diode were used as DFG pump sources. This source generated mid-IR at 3 microns with a powers of ~2.5 microW and a spectral linewidth of less than 30 MHz. A frequency tuning range of 300 GHz (10 cm-1) was obtained by varying the current and temperature of the DFB laser diode. A high-resolution NH3 absorption Doppler-broadened spectrum at 3295.4 cm-1 (3.0345 microns) was obtained at a cell pressure of 27 Pa from which a detection sensitivity of 24 ppm m was estimated.

NASA Discipline Environmental Health↗
NASA NTRS2008

Kinetic Temperature and Electron Density Measurement in an Inductively Coupled Plasma Torch using Degenerate Four-Wave Mixing

Laser wave mixing is presented as an effective technique for spatially resolved kinetic temperature measurements in an atmospheric-pressure radio-frequency inductively-coupled plasma. Measurements are performed in a 1 kW, 27 MHz RF plasma using a continuous-wave, tunable 811.5-nm diode laser to excite the 4s(sup 3)P2 approaches 4p(sup 3)D3 argon transition. Kinetic temperature measurements are made at five radial steps from the center of the torch and at four different torch heights. The kinetic temperature is determined by measuring simultaneously the line shape of the sub-Doppler backward phase-conjugate degenerate four-wave mixing and the Doppler-broadened forward-scattering degenerate four-wave mixing. The temperature measurements result in a range of 3,500 to 14,000 K+/-150 K. Electron densities measured range from 6.1 (+/-0.3) x 10(exp 15)/cu cm to 10.1 (+/-0.3) x 10(exp 15)/cu cm. The experimental spectra are analyzed using a perturbative treatment of the backward phase-conjugate and forward-geometry wave-mixing theory. Stark width is determined from the collisional broadening measured in the phase-conjugate geometry. Electron density measurements are made based on the Stark width. The kinetic temperature of the plasma was found to be more than halved by adding deionized water through the nebulizer.

Schafer, Julia↗
NASA NTRS2020

Chandra spectral measurements of the O supergiant ζ Puppis indicate a surprising increase in the wind mass-loss rate over 18 yr

New long Chandra grating observations of the O supergiant ζ Pup show not only a brightening of the X-ray emission line flux of 13 per cent in the 18 yr since Chandra’s first observing cycle, but also clear evidence – at more than 4σsignificance – of increased wind absorption signatures in its Doppler-broadened line profiles. We demonstrate this with non-parametric analysis of the profiles as well as Gaussian fitting and then use line-profile model fitting to derive a mass-loss rate of 2.47±0.09×10−6Myr−1, which is a 40 per cent increase over the value obtained from the cycle 1 data. The increase in the individual emission line fluxes is greater for short-wavelength lines than long-wavelength lines, as would be expected if a uniform increase in line emission is accompanied by an increase in the wavelength-dependent absorption by the cold wind in which the shock-heated plasma is embedded.

David H. Cohen↗