PHOTOABSORPTION PROBABILITY FOR A SYSTEM GOVERNED BY A TIME-DEPENDENTHAMILTONIAN THROUGH THE (T,T')-FORMALISM

Heller's expression for the absorption cross-section in the weak field limit is extended to cases where the total Hamiltonian contains a str ong time-dependent component, supplemented by a weak field. A very sim ilar expression to the original case then results when the (t,t') form alism is used; one only needs to construct a correlation function for the system without the weak field, and use it to extract the absorptio n probability for any value of the weak-field frequency (or pulse shap e). In addition, a numerical approach for extracting Floquet states wi thout full-matrix diagonalization is demonstrated, by filtering (or fi lter-diagonalization) a single wave function (or the correlation funct ion) propagated under the (t,t') Hamiltonian. (C) 1997 American Instit ute of Physics.