摘要:

A fundamental understanding of coherent electromagnetic radiation processes, which is most rigorously based on quantum electrodynamics, is important for investigating the basic radiative interactions of condensed matter systems, relativistic free electrons in strong fields, and atomic systems in intense laser fields. There has been considerable recent interest in the investigation of coherent radiative interactions involving energetic electrons in crystal lattices, in spatially-periodic static-field structures (such as magnetic wigglers and undulators), and in electromagnetic fields (laser beams). There has also been current interest in radiation processes involving multiply-charged many-electron ions in high- temperature plasmas and in intense laser fields. The attention directed at these processes has been motivated in part by the need to assess various mechanisms for the generation of amplified spontaneous emission at short photon wavelengths (approaching the X-ray region). A precise theoretical treatment for these laser mechanisms and for other coherent electromagnetic radiation processes in the presence of strong fields will necessarily involve quantum-electrodynamics descriptions of the interaction between the electronic system and the electromagnetic field.

ISSN:1042-0150    

DOI:10.1080/10420159108220496

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We show that the powerful method of Floquet-Green's function can be applied to both non-relativistic and relativisit problems of interaction of an electron with a binding potential and a strong electromagnetic field. In part I we present the solution of the Schrödinger associated with a 1D polymer crystal subjected to a strong laser field, where the crystal potential is represented by a periodic delta potential and discuss some of the consequences. In part II, we give the exact solution of the relativistic problem of a Dirac electron interacting with a model-potentialandan e.m. field. The potential is chosen to support a bound state as well as the entire set of continum states of the electron in the absence of the field. The total Feynman propagator and the total wave function of the system, satisfying the Stükelberg-Feynman boundary condition are given in the useful Floquet representation. The basic transition amplitude for transition of the electron from the state () to (s′), where,, ands,s′ are the momentum and spins of the electron, due to absorption or emission of N-photons is obtained.

ISSN:1042-0150    

DOI:10.1080/10420159108220497

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

By solving a model photodetachment problem, we show how the standard Floquet wave function for a system driven by a harmonic potential is modified by the presence of coupling to the continum.

ISSN:1042-0150    

DOI:10.1080/10420159108220498

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We present a brief description of somegeneralizedFloquet formalisms and numerical methods recently developed in our laboratory fornonperturbativetreatments of the time-development of wave functions or density matrix operator of quantum systems driven by intense periodic or multi-color (multi-frequency) laser fields. Both the Schrodinger and Liouville equations are considered. In all cases, it is shown that the time-dependent (monochromatic or polychromatic) problems can beexactlytransformed into equivalent time-independent infinite-dimensional (Hermitian or non-Hermitian) matrix (or super matrix) eigenvalue problems. These yield numerically stable and computationally efficient techniques for the unified treatment of one- and multiple- photon, resonant and non-resonant, steady-state and transient phenomena in strong fields. Applications of the methods to intense-fielde multiphoton and nonlinear optical processes of current significance are briefly discussed.

ISSN:1042-0150    

DOI:10.1080/10420159108220499

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We present new developments in nonadiabatic geometric phases along two lines for systems undergoing changes of quantum state in intense fields. We first present a geometric representation of the non-Hermitian Schrodinger equation and introduce the notion of acomplexmultiphoton Aharonov-Anandan (AA) phase associated with dissipative two-level systems driven by periodic fields. The concept is further extended to include field modulation effects. We then develop the AA phase for spin-jsystems in periodic fields and find conditions for cyclic evolution for general multi-level systems. In both cases, generalizations of the Floquet formalism lead to general analytical expressions for geometric phases that can be tested by experiments.

ISSN:1042-0150    

DOI:10.1080/10420159108220500

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We develop a method that allows the investigation of adiabatic evolution in periodically driven quantum systems. It is shown how Berry's geometrical phase emerges in quantum optics. We analyse microwave experiments performed on Rydberg atoms and suggest a new, non-perturbative mechanism to produce excited atomic states.

ISSN:1042-0150    

DOI:10.1080/10420159108220501

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A nonerturbative approach to such problems has been developed, based on a Liouville-space expansion of the solution of Heisenberg equation of motion for the relevant operators as a series of time-independent basis elements with time-dependent coefficients to be determined. Since the method is applicable to nonlinear dynamics of both classical and quantum systems, these two cases are treated in parallel. The necessary nonlinear dependence on initial conditions is introduced by allowing Liouvellian eigenvalues to depend on constants of motion. The formalism is illustrated by application to the anharmonic classical oscillator and the quantum Jaynes-Cummings model.

ISSN:1042-0150    

DOI:10.1080/10420159108220502

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Recently, the possibility of obtaining ISE in spectral bands of forbidden light propagation (photonic bandgaps) has been suggested by Yablonovitch.1These bandgaps are spectral regions admitting only complex wavevectorsk(evanescent waves) in any direction, and boundecl by frequencies ωmax((min)at which the dispersion curve ω(k) becomes discontinuous. Because they are associated with definite k (band edges), such hndgaps are delocalized in space, i.e., they inhibit spontaneous emissionindependently of t.he spatial distribution of emittersin the system. The systems that have been proposed1for the demonstration of bandgaps are dielectric superlattices that exhibit strong three-dimensional (3D) periodic moclulations of the dielectric index with a period comparable to half the emission wavelength.

ISSN:1042-0150    

DOI:10.1080/10420159108220503

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The method of using dressed states in the presence of an external electromagnetic plane wave is applied to paired electrons in a thin film of normal superconductors. The ground state wave function is analyzed using the Ginzburg-Landau model, while the electron wave functions are determined by relating the Ginzburg-Landau model to the BCS model. The condensate and electron wave functions are dressed by an external electromagnetic field which creates a standing wave inside the thin film. The dissociation of the electron pairs near the Fermi surface is calculated and a differential cross-section is found which describes the flow of dissociated electrons under the influence of the electromagnetic field.

ISSN:1042-0150    

DOI:10.1080/10420159108220504

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The main purpose of this talk is to acquaint the audience with interesting properties of the mass shift of electron in a homogeneous constant field, especially with its classical asymtoticsarising at small quantum parameters (2), when β1,β2, χ≪1. The unusual properties of this shift are:1.classicity and at the same time its absence in classical Abraham-Lorentz-Dirac equation;2.nonlocality expressing formation on the length ∼mc2/eϵ much greater than Compton lengthh/mc;3.linearity in the modulus ofeϵ, i.e. nonanalyticity and, consequently, nonperturbativity in the external field ϵ4.independence of spin of a particle but dependence on spin of proper field.Although the shift does not change the classical equation of motion, it does alter the action and should therefore manifest itself in quantum-mechanical processes. For example, in pair creation by electric field in vacuum described by imaginary part of Lagrange function of external field.

ISSN:1042-0150    

DOI:10.1080/10420159108220505

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor