ABSTRACT In this article we discuss aspects of correlations and entanglements in condensed gases.... more ABSTRACT In this article we discuss aspects of correlations and entanglements in condensed gases. This requires us to look at the quantum fluctuations in the field that describes the condensates. We discuss ways in which these effects can be observed in experiments and used in precision measurements.
Abstract The subject of this review is the collisional redistribution of resonance atomic radiati... more Abstract The subject of this review is the collisional redistribution of resonance atomic radiation in dilute gases. The formation of scattered spectra in weak and intense fields is discussed and the formation that may be obtained from experiments is presented. The focus of recent work in the field is on radiative events taking place during collisions. Different aspects of the problem are presented using mainly the density matrix and correlation function approach. This work has shown what types of information on interatomic potentials and collision dynamics can be obtained using near-resonant light scattering from gases: this is highlighted in a discussion of light scattering in the presence of depolarizing collisions. We discuss the relationship of work on collisional redistribution to the various “half-collision” experiments that have recently come to the fore.
We report the changes observed in intense (∼1015 W cm−2) 1-μm-wavelength laser pulses propagating... more We report the changes observed in intense (∼1015 W cm−2) 1-μm-wavelength laser pulses propagating through argon and krypton at a range of densities below and above atmospheric. The transmitted pulses show blue shifting of the fundamental spectrum and defocusing of the spatial profile. Our interpretation is aided by simultaneous measurements of the plasma luminescence and also by comparison with a two-dimensional numerical model. We infer from our results that laser-induced collisional ionization is important at the higher gas densities even when pulses with a duration as short as 2 ps are used.
Abstract We present a simple model for two-electron excitation and ionization of an atom in the p... more Abstract We present a simple model for two-electron excitation and ionization of an atom in the presence of an intense laser field. We show, in particular, how the Coulomb interaction, via configuration interaction, prevents the excitation and ionization from being collective in all but the most intense fields. By collective we mean that each electron has the same spatial wavefunction: this implies that the electron pair may be described by a restricted time-dependent Hartree-Fock wavefunction. The configuration interaction prevents collective behaviour not only through the process of auto-ionization but also through the mixing of doubly excited independent electron states into the ground state. We are able to give criteria for establishing true collective excitation and ionization of our model two-electron system in an intense field.
A theoretical model has been developed to study the propagation and amplification of hypershort (... more A theoretical model has been developed to study the propagation and amplification of hypershort (< 200 fs) pulses in excimer laser amplifiers, dealing specifically with coherent propagation effects and giving a detailed description of the dissociation of the ground state for a linear potential. The model equations are presented and the physical significance of the terms discussed.
We consider the localization of a pair of particles in relative-position space. We show how a seq... more We consider the localization of a pair of particles in relative-position space. We show how a sequence of scattering interactions progressively entangles two particles, giving rise to a robust state of well-defined separation and thus providing a natural description of relative position. We use two thought experiments to describe the localization process. The first is an interferometer with recoiling mirrors. The second, and more general, case considers photons scattering from a pair of particles and the resulting emergence of a Young's interference pattern. The underlying framework of the localization process suggests a prominent role for entanglement and relative observables at the boundary between quantum and classical mechanics.
ABSTRACT In this article we discuss aspects of correlations and entanglements in condensed gases.... more ABSTRACT In this article we discuss aspects of correlations and entanglements in condensed gases. This requires us to look at the quantum fluctuations in the field that describes the condensates. We discuss ways in which these effects can be observed in experiments and used in precision measurements.
Abstract The subject of this review is the collisional redistribution of resonance atomic radiati... more Abstract The subject of this review is the collisional redistribution of resonance atomic radiation in dilute gases. The formation of scattered spectra in weak and intense fields is discussed and the formation that may be obtained from experiments is presented. The focus of recent work in the field is on radiative events taking place during collisions. Different aspects of the problem are presented using mainly the density matrix and correlation function approach. This work has shown what types of information on interatomic potentials and collision dynamics can be obtained using near-resonant light scattering from gases: this is highlighted in a discussion of light scattering in the presence of depolarizing collisions. We discuss the relationship of work on collisional redistribution to the various “half-collision” experiments that have recently come to the fore.
We report the changes observed in intense (∼1015 W cm−2) 1-μm-wavelength laser pulses propagating... more We report the changes observed in intense (∼1015 W cm−2) 1-μm-wavelength laser pulses propagating through argon and krypton at a range of densities below and above atmospheric. The transmitted pulses show blue shifting of the fundamental spectrum and defocusing of the spatial profile. Our interpretation is aided by simultaneous measurements of the plasma luminescence and also by comparison with a two-dimensional numerical model. We infer from our results that laser-induced collisional ionization is important at the higher gas densities even when pulses with a duration as short as 2 ps are used.
Abstract We present a simple model for two-electron excitation and ionization of an atom in the p... more Abstract We present a simple model for two-electron excitation and ionization of an atom in the presence of an intense laser field. We show, in particular, how the Coulomb interaction, via configuration interaction, prevents the excitation and ionization from being collective in all but the most intense fields. By collective we mean that each electron has the same spatial wavefunction: this implies that the electron pair may be described by a restricted time-dependent Hartree-Fock wavefunction. The configuration interaction prevents collective behaviour not only through the process of auto-ionization but also through the mixing of doubly excited independent electron states into the ground state. We are able to give criteria for establishing true collective excitation and ionization of our model two-electron system in an intense field.
A theoretical model has been developed to study the propagation and amplification of hypershort (... more A theoretical model has been developed to study the propagation and amplification of hypershort (< 200 fs) pulses in excimer laser amplifiers, dealing specifically with coherent propagation effects and giving a detailed description of the dissociation of the ground state for a linear potential. The model equations are presented and the physical significance of the terms discussed.
We consider the localization of a pair of particles in relative-position space. We show how a seq... more We consider the localization of a pair of particles in relative-position space. We show how a sequence of scattering interactions progressively entangles two particles, giving rise to a robust state of well-defined separation and thus providing a natural description of relative position. We use two thought experiments to describe the localization process. The first is an interferometer with recoiling mirrors. The second, and more general, case considers photons scattering from a pair of particles and the resulting emergence of a Young's interference pattern. The underlying framework of the localization process suggests a prominent role for entanglement and relative observables at the boundary between quantum and classical mechanics.
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Papers by K. Burnett