Bremsstrahlung in laser-assisted scattering

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Abstract
The process of spontaneous radiation accompanying the scattering of a charged particle by a center of force is studied under conditions in which the scattering takes place in an intense, low-frequency laser field. Approximations are developed which provide expressions for both the amplitude and the total rate for spontaneous bremsstrahlung in the presence of the external field, given in terms of the physical (on-shell) amplitude for bremsstrahlung in the absence of the field. Of particular interest is the effect of the external field on the radiation probability when there is a narrow resonance in the field-free scattering. An explicit analytic approximation is obtained for the spectrum of spontaneous radiation in the resonant case; a series of peaks is found, with spacing between adjacent peaks equal to the frequency of the external field. The effect may be thought of as a continuum analog of the process of intense-field harmonic generation. A simple model, constructed with the aid of a low-frequency approximation for the amplitude for bremsstrahlung in the absence of the external field, is evaluated numerically in order to illustrate this resonance-replication effect. DOI: http://dx.doi.org/10.1103/PhysRevA.48.505 © 1993 The American Physical Society