Doppler broadening

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

Coherent spectroscopy of degenerate two-level systems in Cs

Abstract: Coherent spectroscopy of degenerate two-level systems of the Doppler-broadened ${D}_{2}$ cesium line has been performed in vacuum and in buffer gas cells Subnatural-width (SNW) electromagnetically induced transparency and electromagnetically induced absorption (EIA) resonances have been observed with single-frequency laser excitation for different light polarizations and collision regimes SNW-EIA resonances with linearly polarized excitation of the ${F}_{g}=4$ level are observed, and they increase their contrast with power density increase and reach a contrast of 20% at $200 \mathrm{mW}{\mathrm{cm}}^{\ensuremath{-}2}$ A theoretical model has been elaborated, taking into account the Doppler broadening of the transitions, the linewidth of the laser light, and the experimental conditions for observation of the fluorescence Here the theoretical results are in agreement with those of the experiment In a buffer gas cell, the SNW resonances in the fluorescence, in degenerate two-level systems are observed for the first time and they are only obtained with circularly polarized light A theoretical explanation of this result is proposed At the expense of contrast, in the presence of a buffer gas the coherent resonances are significantly narrower than in a vacuum cell for the same power density The observation of SNW resonances in buffer gas is significantly less sensitive to the laser frequency drift than in a vacuum cell, which could be advantageous for applications in metrology and in the measurement of weak magnetic fields

Energy Levels and Spectral Broadening of Neodymium Ions in Laser Glass

Abstract: Energy levels, linewidths, and oscillator strengths for trivalent neodymium ions in a commercial laser glass were determined from the fluorescence and absorption spectra. The spectra were composed of broad groups of overlapping lines and were deciphered from spectral variations produced by changes in glass temperature from 4° to 300°K. No thermal variation of the peak wavelengths and linewidths of the component lines was observed in this temperature range. The free ion levels of neodymium were completely split into J+½ Kramers doublets by the perturbation of the glass environment on the ion. The splitting patterns correlated closely with those determined from Nd2O3 crystals, indicating that the rare‐earth ion locates in an environment in glass much like the sesquioxide crystal environment.

Spectral broadening of lower hybrid waves produced by parametric instability in current drive experiments of tokamak plasmas

Abstract: In order to explain the results of the non-inductive current produced in the lower hybrid current drive (LHCD) experiments, a broadening of the radiofrequency (RF) power spectrum coupled to tokamak plasma needs to occur. The presented modelling, supported by diagnostic measurements, shows that the parametric instability (PI) driven by ion sound quasimodes, which occur in the scrape-off plasma layer located near the antenna mouth, produces a significant broadening of the launched LH spectrum. Considering the parameters of LHCD experiments of JET (Joint European Torus), and other machines as well, the PI growth rate is high enough for producing the compensation of the convective losses and, consequently, the broadening of a small fraction (of the order of 10%) of the launched power spectrum. Such a phenomenon is identified to be intrinsic to the RF power coupling in the LHCD experiments. As the principal implication of considering such spectral broadening in modelling the LH deposition profile, experiments of LHCD-sustained internal transport barriers in JET were successfully interpreted, which evidenced the effects of a well-defined LH deposition profile. The present work is important for addressing the long-lasting debate on the problem of the so-called spectral gap in LHCD. The design of LHCD scenarios relevant to the modern fusion research programme, an important requirement of which is the control of the plasma current profile in the outer half of plasma, can be properly achieved by considering PI-induced spectral broadening.