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International Conference on Spectral Line Shapes (ICSLS)

Ionic spectra under strong laser field in plasma

David A. Shapiro, М. Г. Степанов

Published Jan 1, 1999• 0 citations
Publisher

Abstract

An expression is found for the profile of Bennett hole with different level lifetimes under strong field and weak collisions. It is shown that the square of the total width being equal to the sum of the squares of the diffusion and field widths. Probe-field spectrum of the three-level system is obtained in the presence of the strong field at the adjacent transition. The Autler - Townes doublet components are shown to broaden and repel each other under the collisions. The main reason of both the effects occurs to be the diffusion of phase due to quadratic frequency shift.

DOI
10.1063/1.58371

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An expression is found for the profile of Bennett hole with different level lifetimes under strong field and weak collisions. It is shown that the square of the total width being equal to the sum of the squares of the diffusion and field widths. Probe-field spectrum of the three-level system is obtained in the presence of the strong field at the adjacent transition. The Autler - Townes doublet components are shown to broaden and repel each other under the collisions. The main reason of both the effects occurs to be the diffusion of phase due to quadratic frequency shift.
An analytical expression is found for the profile of Bennett hole with different level lifetimes under strong field and weak collisions. The expression is valid while the diffusion and field broadening being more than the homogeneous one, but less than the thermal width. It is shown that the square of the total width being equal to the sum of the squares of the diffusion and field widths. The shape of saturation curve is calculated including weak collisions. The formula obtained describes the smooth transition from homogenous to inhomogeneous saturation throughout the new intermediate region. Probe-field spectrum of the three-level system is computed in the presence of the strong field at the adjacent transition. The Autler-Townes doublet components are shown to broaden and repel each other under the collisions. The main reason of both the effects occurs to be the diffusion of phase due to quadratic frequency shift.
The absorption spectrum of a gas with a large Doppler width and soft collisions between particles is studied. The particles are assumed to have a nonlinear dependence of the resonance frequency on velocity. The shape of the narrow peak in the spectrum resulting from an extremum of this dependence is calculated analytically for the first time. In the absence of collisions it has a characteristic asymmetric shape. Collisions are shown to broaden the line and change its shape. The profile of the probe-field spectrum is obtained for a three-level system with the strong field at an adjacent transition. The components of the Autler-Townes doublet are found to spread and repel each other because of collisions.
We have measured the shape of the Autler-Townes doublet and the peak of electromagnetically induced transparency (EIT) under plasma conditions. We compare the experimental results with the calculated spectrum of the probe field of a three-level ArII Λ-scheme by taking into account Coulomb collisions. We show that the Coulomb broadening of the EIT peak is small (less than 40%), while the saturation resonance is broadened under the experimental conditions by a factor of 3. In contrast to the saturation resonance attributable to the Bennett dip in the velocity distribution of the population, the EIT peak is a coherent effect and is broadened mainly through Coulomb dephasing.
The spectrum of weak probe field absorption (amplification) by two-level atoms experiencing collisions with buffer gas atoms in a strong resonance laser field is studied theoretically. Analysis is carried out for systems with a weak Doppler broadening under relatively mild constraints on the strong field intensity for the general case of an arbitrary change in the phase of the radiation-induced dipole moment in elastic collisions of gas particles. It is shown that, in spite of uniform broadening of the absorption line, the probe field spectrum exhibits a clearly manifested anisotropy to mutual orientation of the wavevectors of strong and probe radiation. It is found that the width of resonances in the probe field spectrum under definite conditions (that can easily be created in experiments) is proportional to the diffusion coefficient for atoms interacting with radiation. This fact can form the basis of the spectroscopic method for measuring the transport frequencies of collisions between particles absorbing radiation and buffer particles. It is shown that phase memory effects in collisions strongly modify the probe field spectrum both qualitatively and quantitatively. Simple operative formulas proposed for the probe field spectrum are convenient for experimental data processing.
A theoretical investigation is reported of the Raman scattering and fluorescence (doublet) spectra of three-level quantum systems subjected to a strong laser field reducing broadening of the spectral lines caused by adiabatic perturbations (elastic collisions). The dependences of the frequency shifts, widths, and integrated intensities of the spectral components of the doublet on the intensity and frequency of the laser field are derived allowing for the influence of this field on the collision dynamics.