TIME-FREQUENCY THEORY OF PUMP-PROBE ABSORPTION-SPECTROSCOPY

A variation of density matrix formulation based on the nature of held- matter interference in a mixed time-frequency domain is developed to s tudy molecular pump-probe absorption spectra in condensed phases. Cons idered are both the integrated probe transmitant signals and the frequ ency-dispersed transient absorption coefficients for molecular systems with either two or three electronic surfaces involved. The present fo rmulation is exact and applicable to any field with arbitrary timescal e and shape, and it is valid when the pulses are overlapped as well as separated. The dual temporal-spectral effect of both the excitation a nd detection fields can be clearly elucidated via a transformation tha t preserves causality, The resulting field-matter interference picture of transient absorption in the correlated time-frequency domain is co nceptually natural and physically transparent. The molecular dynamics, and the field-matter temporal/spectral coherence and interference phe nomena can all be clearly demonstrated. (C) 1997 American Institute of Physics.