Semiclassical calculation of transition matrix elements for atoms in external fields

Closed-orbit theory is generalized to the semiclassical calculation of cross-correlated recurrence functions for atoms in external fields. The cross-correlation functions are inverted by a high-resolution spectral analyzer to obtain the semiclassical eigenenergies and transition matrix elements. The method is demonstrated for dipole transitions of the hydrogen atom in a magnetic field. This is an alternative semiclassical calculation of individual quantum transition strengths from closed-orbit theory.