Doppler broadening

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

Dependence of semiconductor laser linewidth on measurement time: evidence of predominance of 1/f noise

Abstract: Linewidths of 1.3 µm InGaAsP lasers were measured by using delayed self-heterodyne set-ups with two different delay-line lengths, i.e. with two equivalent measurement times. It has been found that in high-power operation the linewidth increases as the measurement time becomes longer, and that this dependence is explained well by a calculation assuming that the 1/f noise in the FM noise spectrum is the predominant cause of the spectral broadening. The significance of this fact in coherent optical communications is discussed.

An analytical model for collisional effects on spectral line shape from the Doppler to the collision regime

Abstract: A spectral line shape model accounting for both the collisional confinement narrowing of the Doppler distribution and the inhomogeneous effects due to the radiator speed dependence of the collisional broadening and shifting parameters is proposed. The velocity changes are assumed to be induced as well by hard as soft collisions. Doppler-collision correlations and speed-class exchanges are taken into account. A comparison with the previous models used for the Doppler regime and for the collisional one is done. The present model also applies for the intermediate regime where the two above mechanisms are simultaneously efficient. The spectral line shape characteristics are exemplified through the H2–Ar and C2H2–Xe prototype molecular systems.

On a heating mechanism for cold hydrogen and deuterium atoms produced at the edge of a tokamak plasma

Abstract: Spectroscopic measurements of the D and H line profiles emitted within the edge region of a tokamak plasma, have revealed the existence of a cold central component, broadened mainly by the Zeeman effect arising from the confining magnetic field. Evaluation of the Doppler broadening suggests that the cold component is probably produced by electron impact-induced molecular dissociation, dissociative excitation being one of the few mechanisms which can explain the formation of atoms of kinetic energy around 0.2 eV against a background of comparatively hot electrons and ions. Further analysis of these line profiles, observed along different directions in the equatorial plane and under various tokamak discharge conditions, reveals, in addition to this effective `cold temperature', an effective `lukewarm temperature', which we explain in terms of an appreciable collisional heating mechanism. Estimates of the rates for ion-induced dipole and ion-induced quadrupole collisions with excited atoms, yield values of the correct order of magnitude for this observed `lukewarm temperature'. In addition, measurements of Balmer- line profiles, radiated from a gas discharge in a magnetic field of similar magnitude, are analysed and their shapes compared with those from the tokamak plasma.

The interaction of solutes with their environments

Abstract: The origins of electronic spectral broadening in solutions, glasses and proteins are discussed via three pulse stimulated echo peak–shift measurements. Spectral densities for dye molecules in polar solutions are presented and discussed in terms of molecular models for the dynamics. The breakdown of the harmonic bath picture at low frequencies is presented. Finally, echo measurements on light harvesting complexes of purple bacteria are presented and it is shown that the energy transfer timescale can be obtained from peak–shift measurements.