Calculation of Free-Free Radial Dipole Transition Amplitudes: An L² Basis Approach

Abstract

As part of a larger project to develop efficient procedures for computing strong-field multiphoton ionization of atoms, we have discovered a way of calculating radial free-free transition amplitudes using a Slater-type basis of much the same kind as is used in existing atomic structure codes. This will allow the method to be extended from the hydrogen atom test results presented here to many-electron atoms. Since finite L² basis approximations of free-free amplitudes cannot be expected to converge, an acceleration scheme based on the epsilon algorithm was introduced and a few important lessons were learned about how best to extrapolate from a ten-to-fifteen-basis-function expansion to completeness. In particular, to investigate how to project out channel amplitudes from complex-coordinate calculations, we allowed the Slater exponent in the basis to take on complex values.