Lewis Klein

Relaxation processes and spectra in liquids and dense gases

The spectral response of a molecule dissolved in a liquid or dense gas is calculated using a correlation function approach. It is shown that the characteristic spectra of the molecule can be used as a probe of the molecular motions and the dynamic structure effects. A method developed by Blume and Kubo which assumes the solute–solvent interaction parameter to be a stochastic process is employed. The induced Q branch in the vibration–rotation spectra of polar molecules is discussed as an example and the cases in which the rotational relaxation of the molecule is determined by either the dynamic structure or by collisional processes are obtained in the appropriate limits.

Green's function theory of atomic line broadening in plasmas

Abstract A Greens function method is developed for the calculation of the line shape of the radiation from an atom in a plasma. It is shown that the width of the line is proportional to the imaginary part of the reciprocal of the dielectric function of the plasma. The theory includes electron correlations and quantum effects and thus results in convergent expressions for the line shape. It is also shown that for equilibrium plasmas, no resonance in the line shape occurs at frequency separations equal to the plasma frequency.

Two photon magnetooptic effects

Abstract The theory of two photon magnetooptic effects such as polarization rotation and circular dichroism is developed. An effect which has not been previously discussed, the optical analog of the Hanle effect, is proposed.

Spectroscopic Determination of Core Gradients in Inertial Confinement Fusion Implosions

We report on a collaborative effort that has led to the development of a spectroscopic method for the determination of the gradient structure in ICF implosion cores based on the self‐consistent analysis of simultaneous X‐ray monochromatic images and X‐ray line spectra. This technique is applied to a series of stable and spherically symmetric implosion experiments where Ar‐doped D2‐filled plastic shells were driven with the GEKKO and OMEGA laser systems. Argon K‐shell X‐ray line spectra were measured with streak crystal spectrometers, while X‐ray monochromatic imagers recorded core images based on the Ar Heβ line. The analysis self‐consistently determines the temperature and density gradients that yield the best fits to both the spatial distribution of monochromatic emissivity and spectral line shapes. A multi‐objective genetic algorithm is used to efficiently perform the analysis. This measurement is critical for understanding the spectra formation and plasma dynamics associated with the implosion process...

Spectroscopic Determination of Gradients in Indirect‐Drive OMEGA Implosion Cores

We report here on a spectroscopic method for determining the gradient structure in implosion cores based on the self‐consistent analysis of simultaneous X‐ray monochromatic images and X‐ray line spectra. This technique is applied to a series of stable and low convergence indirect drive experiments where Ar‐doped D2‐filled plastic shells were imploded with the OMEGA laser system. Argon K‐shell X‐ray line spectra were measured with streak crystal spectrometers, and X‐ray monochromatic imagers recorded Ar Heβ based images of the core. The analysis self‐consistently determines the temperature and density gradients that yield the best fits to the monochromatic spatial emissivity profiles and spectral line shapes. This measurement is critical for understanding the atomic kinetics, radiation transfer and plasma dynamics associated with the implosion process. In addition, since the results are independent of hydrodynamic simulations they are important for the verification and benchmarking of detailed fluid dynami...

Radiative redistribution modeling for hot and dense plasmas

A model based on an extension of the Frequency Fluctuation Model (FFM) is developed to investigate the two-photon processes and particularly the radiative redistribution functions for complex emitters in a wide range of plasmas conditions. The FFM, originally, designed as a fast and reliable numerical procedure for the calculation of the spectral shape of the Stark broadened lines emitted by multi-electron ions, relies on the hypothesis that the emitter-plasma system can be well represented by a set of “Stark Dressed Transitions,” SDT. These transitions connected to each others through a stochastic mixing process accounting for the local microfield random fluctuations, form the basis for the extension of the FFM to computation of non-linear response functions. The formalism of the second order radiative redistribution function is presented and examples are shown.

Redistribution of resonance radiation in hot and dense plasmas

The development of a numerical procedure for the study of the resonant two photon plasma spectral properties is presented. The formalism is based on an extension of the Frequency Fluctuation Model (F.F.M.) that permits the calculation of the spectral line shape of Stark broadened lines emitted by multi-electrons ions and takes into account ion dynamics effect. We present an application for the study of resonant scattering by a calculation of the radiative redistribution function for the 3d-2p transition of MgIV.

Line shapes in nonlinear spectroscopy

The shape of the spectral lines of an optically active system interacting with one or more strong radiation fields in the presence of a perturbing bath is studied. A method based on the statistics of the fluctuation of the interaction between the radiator and the perturbing environment (the model Markov microfield theory) is used. This method permits the foundations of line shape theory in modern statistical mechanics to be seen clearly. Multiphoton processes and homogeneous, inhomogeneous, and power broadening mechanisms are included in the analysis. The correlations between radiative and collisional processes which arise in nonlinear spectroscopy are included explicitly. A discussion of the new information that is obtained from these correlations in nonlinear spectroscopy is also presented. Several model systems are presented as illustrative examples of the theory.