Doppler broadening

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

Comb-locked Lamb-dip spectrometer

Abstract: Overcoming the Doppler broadening limit is a cornerstone of precision spectroscopy. Nevertheless, the achievement of a Doppler-free regime is severely hampered by the need of high field intensities to saturate absorption transitions and of a high signal-to-noise ratio to detect tiny Lamb-dip features. Here we present a novel comb-assisted spectrometer ensuring over a broad range from 1.5 to 1.63 μm intra-cavity field enhancement up to 1.5 kW/cm2, which is suitable for saturation of transitions with extremely weak electric dipole moments. Referencing to an optical frequency comb allows the spectrometer to operate with kHz-level frequency accuracy, while an extremely tight locking of the probe laser to the enhancement cavity enables a 10−11 cm−1 absorption sensitivity to be reached over 200 s in a purely dc direct-detection-mode at the cavity output. The particularly simple and robust detection and operating scheme, together with the wide tunability available, makes the system suitable to explore thousands of lines of several molecules never observed so far in a Doppler-free regime. As a demonstration, Lamb-dip spectroscopy is performed on the P(15) line of the 01120-00000 band of acetylene, featuring a line-strength below 10−23 cm/mol and an Einstein coefficient of 5 mHz, among the weakest ever observed.

Spectroscopic investigations of the plasma behavior in a plasma opening switch experiment

Abstract: The electron density, the electron kinetic energy, the particle motion, and electric fields in a coaxial positive‐polarity plasma opening switch (POS) were studied using spectroscopic diagnostics. A gaseous source that injects the plasma radially outward from inside the inner POS electrode was developed. The plasma was locally seeded with various species, desired for the various measurements allowing for axial, radial, and azimuthal resolutions both prior to and during the 180 ns long current pulse. The electron density was determined from particle ionization times and the electron energy from line intensities and time dependent collisional‐radiative calculations. Fluctuating electric fields were studied from Stark broadening. The ion velocity distributions were obtained from emission‐line Doppler broadenings and shifts. The early ion motion, the relatively low ion velocities and the nearly linear velocity dependence on the ion charge‐to‐mass ratio, leads to the conclusion that the magnetic field penetrat...

Structural modifications induced by ion irradiation and temperature in boron carbide B4C

Abstract: Already used as neutron absorber in the current French nuclear reactors, boron carbide (B 4 C) is also considered in the future Sodium Fast Reactors of the next generation (Gen IV). Due to severe irradiation conditions occurring in these reactors, it is of primary importance that this material presents a high structural resistance under irradiation, both in the ballistic and electronic damage regimes. Previous works have shown an important structural resistance of boron carbide even at high neutron fluences. Nevertheless, the structural modification mechanisms due to irradiation are not well understood. Therefore the aim of this paper is to study structural modifications induced in B 4 C samples in different damage regimes. The boron carbide pellets were shaped and sintered by using spark plasma sintering method. They were then irradiated in several conditions at room temperature or 800 °C, either by favoring the creation of ballistic damage (between 1 and 3 dpa), or by favoring the electronic excitations using 100 MeV swift iodine ions ( S e ≈ 15 keV/nm). Ex situ micro-Raman spectroscopy and Doppler broadening of annihilation radiation technique with variable energy slow positrons were coupled to follow the evolution of the B 4 C structure under irradiation.

Influence of laser intensity on absorption line broadening in laser absorption spectroscopy

Abstract: The influence of laser intensity on absorption line broadening was investigated. Laser absorption spectroscopy was applied to low-pressure plasma, and the translational temperature deduced from the Doppler width was found to increase with laser intensity; this was in contrast to the conventional laser theory. Consequently, the dependency of absorption saturation on the Doppler frequency was considered. The predicted variation in broadening width with laser intensity showed a good agreement with the measurement. In addition, we obtained a correction factor for the temperature measurement at high laser intensity.

Quantum scattering calculations for H2S–He between 1–600 K in comparison with pressure broadening, shift, and time resolved double resonance experiments

Abstract: We have performed quantum scattering calculations to predict pressure broadening, pressure shift, and inelastic depopulation cross-sections for the rotational transitions 11,0←10,1 and 22,0←21,1 of the H2S molecule in collision with helium atoms over a temperature range from 1 to 600 K. The calculated cross-sections are compared with experimental values obtained by millimeter wave spectroscopic techniques and the collisional cooling method. We observe good agreement between theory and experiment over the temperature region from 20 to 600 K, but increasing differences below 20 K. Possible reasons for the deviations at lower temperatures are discussed. The calculations also illustrate the contribution of elastic collisions to the pressure broadening cross-sections.