AUTOCORRELATION FUNCTIONS IN THE PHOTOIONIZATION OF HYDROGEN IN ELECTRIC AND MAGNETIC-FIELDS

The photoionization (PI) cross section of hydrogen in external electric and magnetic fields was studied by a direct version of the recursive residue generation method, combined with complex dilation and discretization. The PI cross section was computed for three different combinations of fields: an electric field only, perpendicular electric and magnetic fields, and, finally, an electric field with an angle of 80°to the magnetic field. The field-induced resonances were shown to have Fano-type profiles, with a shape depending on the field combination. The fluctuations of the base line were studied using an autocorrelation function C(ε). For the field combinations studied here, C(ε) has for small ε an initial Lorentzian shape. With increasing ε different oscillatory structures in C(ε) were observed. The correlation functions were studied for several energy ranges, achieving a common Lorentzian shape for the highest range, independent of the field combinations. A simple interpretation of the behavior for all cases in terms of chaotic ionization is possible. © 1995 The American Physical Society.