Doppler broadening

About: Doppler broadening is a research topic. Over the lifetime, 5509 publications have been published within this topic receiving 92552 citations.

Characteristics of giant optical pulsations from ruby

Abstract: A method of laser modulation is described which produces fast, intense and controllable "giant" laser pulses by "Q-modulation." In experiments with ruby, pulses of peak power up to 15 MW and of duration less than 30 nsec have been studied. The principles of the technique are outlined and early experimental results reviewed. The temporal, spectral and spatial structure of giant pulses produced from ruby by a nitrobenzene Kerr cell modulator is reported. The pulse characteristics found to date yield information about the nature of various relaxation processes in ruby and point the way to further experiments to clarify many questions which are raised. The results a) set an upper limit of 10-7sec on the E-→2A-relaxation time, b) show a shortening of upper-state relaxation time by about seven times under heavy pumping, c) show relaxation of excitation taking place across the laser line in microseconds, d) show progressive spectral broadening for shorter pulses to encompass most of the fluorescent line, e) show increasing asymmetry of spectral output for faster, more intense pulses, and f) show little broadening of beam divergence over normal, but with added structure.

Investigation of OH absorption cross sections of rotational transitions in the A 2 ∑ + , ( υ ′ = 0 ) ← X 2 Π , ( υ ″ = 0 ) band under atmospheric conditions: Implications for tropospheric long‐path absorption measurements

Abstract: The accuracy of tropospheric hydroxyl radical measurements by long-path absorption spectroscopy is ultimately limited by the uncertainty of the effective OH absorption cross sections. The latter were determined from calculated spectra for the Q1(2), Q1(3), and P1(1) rotational lines of the OH A2∑+, (υ′=0)←X2Π, (υ″=0) transition at 308 nm. The calculations took into account Doppler broadening, measured data of the collisional broadening of OH by air molecules, and instrumental line broadening effects. The calculated spectra were compared with OH absorption spectra measured in a flow reactor near room temperature at 1013 hPa. Excellent agreement between calculated and measured OH spectra was achieved using the collision-broadening parameters determined recently by Leonard (1990). The effective absorption cross sections at the line center (peak absorption cross sections) calculated for the Voigt line shape at 300 K and 1013hPa are: σeff(v˜0)[ Q1(2) ]=(1.67±0.1)×10-16 cm2, σeff(v˜0)[ Q1(3) ]=(1.4±0.1)×10-16 cm2, σeff(v˜0)[ P1(1) ]=(1.41±0.1)×10-16 cm2. The full width at half maximum of the spectral lines is 2.5 pm, and the shape factor a is 1.41. Calculations of the effective absorption cross section under different atmospheric conditions demonstrate a strong pressure dependence for all lines. At 2800 m altitude (720 hPa) the peak absorption cross section of the OH Voigt lines is about 35% higher than at sea level. The temperature dependence in an interval of ±20 K around room temperature (at 1013 hPa) is only small (±3% for the Q lines and ±6% for the P1(1) line). The estimated total uncertainty of the effective absorption cross section is 8%.

Linewidths of the Microwave Inversion Spectrum of Ammonia

Abstract: The linewidths of some 25 inversion spectral lines of ammonia in the frequency region of 18–29 kMc/sec have been measured. Corrections due to various effects such as source modulation, cell‐length broadening, and Doppler shift were applied to the experimental data to evaluate the linewidth parameters. Self‐broadening and foreign‐gas broadening by some 15 different gases have been studied. In the case of self‐broadening of the series of lines with J=K for which the effect of rotational resonance is negligible, the width parameters determined experimentally agree well with those calculated by Anderson's theory from (2, 2) to (5, 5), but appreciable deviations are found at higher J. For the lines with J≠K, the discrepancy becomes larger and increases with increasing difference between J and K. The quantum number dependence of the foreign‐gas broadening by methyl chloride and by carbon dioxide has been investigated in detail. For methyl chloride broadening the theoretical and measured widths agree with each other to about the same extent as in self‐broadening, whereas the agreement is somewhat less satisfactory in the case of carbon dioxide. An alternative formulation of the collision theory of line broadening is presented. Here the theory of radiation interruption is treated as a problem of multichannel collision. The essential feature of this formulation is that it includes the higher‐order effects of the collision process rather than just the usual first‐order terms. This analysis leads to suggestions as to possible directions of improving the calculations.

BeppoSAX Observation of 4U 1626?67: Discovery of an AbsorptionCyclotron Resonance Feature

Abstract: We report on an observation of the low-mass X-ray binary 4U 1626-67 performed during the BeppoSAX science verification phase. An absorption feature at ~37 keV, which is attributable to electron cyclotron resonance, has been discovered in its pulse-averaged spectrum. The inferred neutron star magnetic field strength is 3.2(1+z)×1012 G, where z is the gravitational redshift. The feature is deep and narrow and is resolved in both the broadband fit and in the ratio of observed counts to those seen from the Crab pulsar. The cyclotron resonance energy is in good agreement with the empirical relation between cyclotron energy and high-energy cutoff, while its width is in agreement with the expected Doppler broadening of thermal electrons at the cyclotron resonance frequency. The broadband 0.1-200 keV spectrum is well fit by a two-component model: a 0.27±0.02 keV blackbody and a power law with a photon index of 0.89±0.02. This is the first broadband observation made after the change from spin-up to spin-down that occurred in mid-1990: it confirms the harder spectrum with respect to those observed in the 2-10 keV range.

Spectral broadening in Brillouin imaging

Abstract: Brillouin microscopy is an emerging imaging modality that provides fundamental information about mechanical properties of media in a non-contact manner. To date, low numerical aperture (NA) optics have been used, due to noticeable angular broadening of the Brillouin spectrum at higher NAs. In this work, we investigate theoretically and experimentally the dependence of spectral broadening effects in Brillouin imaging on system NA, for both 90° and 180° scattering geometries. Lineshape deformations and broadening are found to be minimised in a backscattering geometry, hence paving the way for high resolution in-vivo mechanical imaging.