Doppler broadening

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

Electron density determination in the divertor volume of ASDEX Upgrade via Stark broadening of the Balmer lines

Abstract: In this article we present the development of a new diagnostic capable of determining the electron density in the divertor volume of ASDEX Upgrade (AUG). It is based on the spectroscopic measurement of the Stark broadening of the Balmer lines. In this work two approaches of calculating the Stark broadening, i.e. the unified theory and the model microfield method, are compared. It will be shown that both approaches yield similar results in the case of Balmer lines with high upper principal quantum numbers n. In addition, for typical AUG parameters the influence of the Zeeman splitting on the high n Balmer lines is found to be negligible. Moreover, an assumption for the Doppler broadening of Tn = 5 eV, which is the maximum Frank–Condon dissociation energy of recycled neutrals, is sufficient. The initial electron density measurements performed using this method are found to be consistent with both Langmuir probe and pressure gauge data.

Impact of nonlinear spectral broadening in ultra-long Raman fibre lasers

Abstract: We present an experimental study of the impact of FWM-induced nonlinear spectral broadening on the effective reflectivity of ultra-long Raman fiber laser cavities of diverse lengths and fiber bases. We observe an exponential decay of the effective reflectivity with growing power. In standard single-mode fiber, effective reflectivity drops of up to 50% for shorter cavity lengths are observed, while the longest cavity length of 82.4km displays power leakage amounting to an effective reduction of reflectivity of approximately 30%. Using different types of fiber we examine the effect of chromatic dispersion on the Stokes wave broadening.

Temperature field measurements in a sooting flame by filtered rayleigh scattering (FRS)

Abstract: Two-dimensional temperature measurements were performed in a sooting, methane-air flame by a modification of the conventional Rayleigh scattering technique. This new technique, filtered Rayleigh scattering (FRS), uses a molecular absorption filter in the detection path to spectrally separate part of the gas-phase Rayleigh scattering from the elastic scattering contributions of soot particles. It also suppresses laser-induced glare and background scattered light from walls and windows. Thus particle and background, unaffected, gas-phase Rayleigh scattering can be detected. This has been done in a weakly sooting flame where the temperature field information was obtained using a calibration of the FRS setup in a nonsooting flame by conventional Rayleigh scattering. This was necessary because the FRS gas scattering intensity is no longer a simple function of temperature and the known scattering cross sections of the individual gas species present. It also depends on the spectral broadening of the Rayleigh line relative to the incident radiation. Two theoretical models for the calculation of the dependence of the RRS signal on the experimental conditions, for the kinetic and the hydrodynamic regime, are presented in order to directly calculate gas-phase temperatures from FRS measurements without the need for calibration. For the present flames, the broadening mechanism is in an intermediate regime.

A diode laser absorption study on a 100 MHz argon ICP

Abstract: Diode laser absorption on the - argon transition is used to measure heavy particle temperatures in a 100 MHz argon inductively coupled plasma. Radial profiles of this temperature are obtained from the Gaussian part of the absorption profile with an accuracy of about 500 K, for four different input powers and at two different heights. The integrated profile is used to calculate the 4s level density and to trace the ionizing and recombining plasma parts. The measurements also show that the method of attributing the Lorentzian width only to Stark broadening for calculating electron densities is not correct for this argon transition in atmospheric plasmas. A second broadening process with Lorentzian shape, Van der Waals broadening, has to be taken into account. Under the measured conditions at the hottest positions in the plasma about 50% of the Lorentz component is due to Van der Waals broadening and this increases to almost 100% at the edges of the plasma.

Multichromophoric cyclodextrins. 2. Inhomogeneous spectral broadening and directed energy hopping

Abstract: A [beta]-cyclodextrin bearing seven 2-naphthoyloxy chromophores is a good model for the study of the effect of the excitation wavelength on energy hopping among chromophores in well-defined positions, as in photosynthetic antennae. Absorption spectra, emission spectra, and excitation polarization spectra were recorded in a propylene glycol-dioxane glass at 200 K. Comparison is made with a bis(naphthoate) bichromophoric molecule. The parallelism between the increase of emission spectrum displacement and fluorescence anisotropy observed for the red edge of most vibronic bands, and especially for the 0-0 one, is established for the first time. It can be interpreted in terms of inhomogeneous spectral broadening due to solvation heterogeneity. The decrease of energy transfer that is observed upon red-edge excitation is evidence that energy hopping is not chaotic but directed toward lower-energy chromophores. 43 refs., 7 figs.