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Results for “Doppler broadening effects”

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 19 records
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NASA NTRS1973

Doppler broadening effect on collision cross section functions - Deconvolution of the thermal averaging

The surprising feature of the Doppler problem in threshold determination is the 'amplification effect' of the target's thermal energy spread. The small thermal energy spread of the target molecules results in a large dispersion in relative kinetic energy. The Doppler broadening effect in connection with thermal energy beam experiments is discussed, and a procedure is recommended for the deconvolution of molecular scattering cross-section functions whose dominant dependence upon relative velocity is approximately that of the standard low-energy form.

Bernstein, R. B.↗
NASA NTRS1986

Correction of Doppler-broadened Rayleigh backscattering effects in H2O dial measurements

A general method of solutions for treating effects of Doppler-broadened Rayleigh backscattering in H2O Differential Absorption Lidar (DIAL) measurements are described and discussed. Errors in vertical DIAL measuremtns caused by this laser line broadening effect can be very large and, therfore, this effect has to be accounted for accurately. To analyze and correct effects of Doppler-broadened Rayleigh backscattering in DIAL experiments, a generalized DIAL approximation was derived starting from a lidar equation, which includes Doppler broadening. To evaluate the accuracy of H2O DIAL measurements, computer simulations were performed. It was concluded that correction of Doppler broadened Rayleigh backscattering is possible with good accuracy in most cases of tropospheric H2O DIAL measurements, but great care has to be taken when layers with steep gradients of Mie backscattering like clouds or inversion layers are present.

Ansmann, A.↗
NASA NTRS1991

Theoretical studies of lasers and converters

Discussed here is Doppler broadening and its effects upon the stimulated emission cross-section connecting an upper level with a lower level in an iodine laser. The stimulated emission cross section is given. The level transitions for the iodine laser are illustrated as are the relative intensities of these transitions. Also discussed is the Voigt profile, which considers the effect of both Doppler broadening and collision broadening upon the absorption line shape. The equations describing the Voigt profile were added to the continuous flow laser model laser simulation program. The results were compared with the standard absorption profile reported in an earlier study. There seems to be no advantage to using the Voigt profile as the laser power output is relatively insensitive to changes in the absorption cross section at the pressures being considered for a space laser. One disadvantage of using the Voigt profile is the excessive numerical computations required by the additional equations.

Heinbockel, John H.↗
NASA NTRS1972

Laser-induced line-narrowing effects in coupled Doppler-broadened transitions. II - Standing-wave features.

Previous theoretical results on the influence of a laser on the line shape of a coupled transition (laser-induced line narrowing) have been restricted to the case where the laser is detuned from the center of its atomic gain profile or is in the form of a traveling wave. The present paper extends these results to the case where the laser is an intense standing-wave field tunable to the center of its atomic gain profile (conditions for Lamb dip). A theoretical solution of the problem is developed, and a detailed discussion of line shapes and physical processes involved is included.

Feldman, B. J.↗
NASA NTRS1972

Abundances in late-type giants.

The narrow-band photometry of Spinrad and Taylor (1969) is analyzed by the synthetic spectra technique. Surface gravities, Doppler broadening velocities, effective temperatures, and metal abundances are determined for 131 K giants. Evolutionary tracks and gravities determined from the photometry are used to give space positions, space velocities, and absolute magnitudes of the 131 stars. We conclude that a class of stars exists with metals and/or nitrogen significantly enhanced with respect to the sun; further that these stars have average space motions similar to those of moderately old Population I stars. The Doppler broadening velocity is found to be a strong function of temperature for K giants, and in some cases, possibly a function of surface gravity.

Gottlieb, D. M.↗
NASA NTRS1974

Correlation effects in the theory of combined Doppler and pressure broadening. I - Classical theory

An investigation is conducted of the combined effects of radiator-perturber collisions and radiator translational motion in the context of foreign gas broadening of optical transitions in neutral radiators. Questions concerning the speed-dependent collision frequency are considered and aspects of general theory are explored, taking into account the correlation function, the ensemble average, and the kinetic equation formalism. An elementary solution is discussed along with a one-perturber approximation, inverse power law model calculations, and a comparison with the Voigt profile.

Ward, J.↗
NASA NTRS1978

Laser amplification of incoherent radiation

The amplification of noise in a laser amplifier is treated theoretically. The model for the active medium and its description using density-matrix techniques, are taken from the theory of laser operation. The spectral behavior of the radiation in the nonlinear regime is studied and the formalism is written from the onset in the frequency domain. The statistics of the light are gradually modified by the nonlinear amplification process, and expressions are derived for the rate of change of fluctuations in intensity as a measure of statistical changes. In addition, the range of validity of Litvak's Gaussian-statistics approximation is discussed. In the homogeneous-broadening case, the evolution of initially broadband Gaussian radiation toward quasimonochromatic oscillations with laserlike statistics is explored in several numerical examples. The connections of this study with the time-domain work on self-pulsing in a ring-laser configuration, are established. Finally, spectral-narrowing and -rebroadening effects in Doppler-broadened media are discussed both analytically and with numerical examples. These examples show the distinct contribution of pulsations in the population ('Raman-type terms'), and saturation phenomena.

Menegozzi, L. N.↗
NASA NTRS2011

Application of Commercial Non-Dispersive Infrared Spectroscopy Sensors for Sub-Ambient Carbon Dioxide Detection

Monitoring carbon dioxide (CO2) concentration within a spacecraft or spacesuit is critically important to ensuring the safety of the crew. Carbon dioxide uniquely absorbs light at wavelengths of 3.95 micrometers and 4.26 micrometers. As a result, non-dispersive infrared (NDIR) spectroscopy can be employed as a reliable and inexpensive method for the quantification of CO2 within the atmosphere. A multitude of commercial-off-the-shelf (COTS) NDIR sensors exist for CO2 quantification. The COTS sensors provide reasonable accuracy so long as the measurements are attained under conditions close to the calibration conditions of the sensor (typically 21.1 C and 1 atm). However, as pressure deviates from atmospheric to the pressures associated with a spacecraft (8.0-10.2 PSIA) or spacesuit (4.1-8.0 PSIA), the error in the measurement grows increasingly large. In addition to pressure and temperature dependencies, the infrared transmissivity through a volume of gas also depends on the composition of the gas. As the composition is not known a priori, accurate sub-ambient detection must rely on iterative sensor compensation techniques. This manuscript describes the development of recursive compensation algorithms for sub-ambient detection of CO2 with COTS NDIR sensors. In addition, the basis of the exponential loss in accuracy is developed theoretically considering thermal, Doppler, and Lorentz broadening effects which arise as a result of the temperature, pressure, and composition of the gas mixture under analysis. As a result, this manuscript provides an approach to employing COTS sensors at sub-ambient conditions and may also lend insight into designing future NDIR sensors for aerospace application.

Swickrath, Michael J.↗
NASA NTRS2012

Application of Commercial Non-Dispersive Infrared Spectroscopy Sensors for Sub-Ambient Carbon Dioxide Detection

Monitoring carbon dioxide (CO2) concentration within a spacecraft or spacesuit is critically important to ensuring the safety of the crew. Carbon dioxide uniquely absorbs light at wavelengths of 3.95 micrometers and 4.26 micrometers. As a result, non-dispersive infrared (NDIR) spectroscopy can be employed as a reliable and inexpensive method for the quantification of CO2 within the atmosphere. A multitude of commercial off-the-shelf (COTS) NDIR sensors exist for CO2 quantification. The COTS sensors provide reasonable accuracy as long as the measurements are attained under conditions close to the calibration conditions of the sensor (typically 21.1 C (70.0 F) and 1 atmosphere). However, as pressure deviates from atmospheric to the pressures associated with a spacecraft (8.0{10.2 pounds per square inch absolute (psia)) or spacesuit (4.1{8.0 psia), the error in the measurement grows increasingly large. In addition to pressure and temperature dependencies, the infrared transmissivity through a volume of gas also depends on the composition of the gas. As the composition is not known a priori, accurate sub-ambient detection must rely on iterative sensor compensation techniques. This manuscript describes the development of recursive compensation algorithms for sub-ambient detection of CO2 with COTS NDIR sensors. In addition, the source of the exponential loss in accuracy is developed theoretically. The basis of the loss can be explained through thermal, Doppler, and Lorentz broadening effects that arise as a result of the temperature, pressure, and composition of the gas mixture under analysis. This manuscript provides an approach to employing COTS sensors at sub-ambient conditions and may also lend insight into designing future NDIR sensors for aerospace application.

Swickrath, Michael J.↗
NASA NTRS2013

Commercial Non-Dispersive Infrared Spectroscopy Sensors for Sub-Ambient Carbon Dioxide Detection

Carbon dioxide produced through respiration can accumulate rapidly within closed spaces. If not managed, a crew's respiratory rate increases, headaches and hyperventilation occur, vision and hearing are affected, and cognitive abilities decrease. Consequently, development continues on a number of CO2 removal technologies for human spacecraft and spacesuits. Terrestrially, technology development requires precise performance characterization to qualify promising air revitalization equipment. On-orbit, instrumentation is required to identify and eliminate unsafe conditions. This necessitates accurate in situ CO2 detection. Recursive compensation algorithms were developed for sub-ambient detection of CO2 with commercial off-the-shelf (COTS) non-dispersive infrared (NDIR) sensors. In addition, the source of the exponential loss in accuracy is developed theoretically. The basis of the loss can be explained through thermal, Doppler, and Lorentz broadening effects that arise as a result of the temperature, pressure, and composition of the gas mixture under analysis. The objective was to develop a mathematical routine to compensate COTS CO2 sensors relying on NDIR over pressures, temperatures, and compositions far from calibration conditions. The routine relies on a power-law relationship for the pressure dependency of the sensors along with an equivalent pressure to account for the composition dependency. A Newton-Raphson iterative technique solves for actual carbon dioxide concentration based on the reported concentration. Moreover, first principles routines were established to predict mixed-gas spectra based on sensor specifications (e.g., optical path length). The first principles model can be used to parametrically optimize sensors or sensor arrays across a wide variety of pressures/temperatures/ compositions. In this work, heuristic scaling arguments were utilized to develop reasonable compensation techniques. Experimental results confirmed this approach and provided evidence that composition broadening significantly alters spectra when pressure is reduced. Consequently, a recursive compensation technique was developed with the Newton-Raphson method, which was subsequently verified through experimentation.

Swickrath, Michael J.↗
NASA NTRS1985

Deconvolution of diode-laser spectra

A new technique has been developed for deconvolving diode-laser spectra. This technique treats Doppler broadening, collisional broadening, and instrumental effects simultaneously. This technique is superior to previous deconvolution methods in the recovery of line-strength and transition-frequency information. A section of the ethane spectrum near 12 microns is used as an example. This new approach applies to any spectroscopy in which the instrumental resolution is narrower than actual linewidths.

Halsey, G. W.↗
NASA NTRSDate not supplied

Direct Measurement of the Ion Temperatures in Tycho's SNR

We present preliminary results of our XMM- Newton/RGS observation of the southeastern ejecta knots in Tycho's supernova remnant. The RGS successfully resolved numerous emission lines including O He-alpha, O Ly-alpha, and Fe L lines. Line broadening was measured to be ~3 eV for the O He-alpha and ~4.5 eV for Fe L lines. If we attribute the broadening to pure thermal Doppler effects, then we obtain kT_O and kT_Fe to be ~400 keV and 1.5 MeV, respectively. These temperatures can be explained by collisionless shock heating with a shock velocity of ~3600 km/s. This is inconsistent with (slightly smaller than) a forward shock speed of ~4300 km/s, suggesting that the knots are heated by a reverse shock. The relative abundance of intermediate-mass elements to oxygen in the knots is more consistent with that expected in a classical W7 model (a single-degenerate scenario) than a violent merger of two white dwarves (a double-degenerate scenario).

Brian Williams↗
NASA NTRS2020

RGS Observations of Ejecta Knots in Tycho's Supernova Remnant

We present results from XMM-Newton/RGS observations of prominent knots in the southest portion of Tycho's supernova remnant, known to be the remnant of a Type Ia SN in 1572 C.E. By dispersing the photons from these knots out of the remnant with very little emission in front of or behind them, we obtained the nearly uncontaminated spectra of the knots. In the southernmost knot, the RGS successfully resolved numerous emission lines from Si, Ne, O He-alpha and Ly-alpha, and Fe L-shell. This is the first clear detection of O lines in Tycho's SNR. Line broadening was measured to be ~ 3 eV for the O He-alpha and ~ 4:5 eV for Fe L lines. If we attribute the broadening to pure thermal Doppler effects, then we obtain kTO and kTFe to be ~ 400 keV and 1.5 MeV, respectively. These temperatures can be explained by heating in a reverse shock with a shock velocity of ~ 3500 km/s. The abundances obtained from fitting the RGS and MOS data together imply substantially elevated amounts of these materials, confi rming previous studies that the knots are heated by a reverse shock, and thus contain ejecta material from the supernova. We are unable to fi nd a Type Ia explosion model that reproduces these abundances, but this is likely the result of this knot being too small to extrapolate to the entire remnant.

Brian J. Williams↗