ABSTRACT
This chapter provides a self-contained introduction to pump-probe
(PP′) spectroscopy of molecular systems from the perspective of the quantum process matrix χ , a formalism that is used to describe
open quantum systems. In doing so, we first present the theory of
PP′ spectroscopy using an intuitive time-dependent approach based on wave packet methods. The theory is accompanied by explicit
analytical calculations using model molecular dimer systems. This
paves the way to the derivation of the central result of this Chapter,
namely, that a frequency-integrated broadband PP′ spectra may be re-expressed as a linear combination of elements associated with
the light-matter interaction (e.g., dipole matrix elements) and the
process matrix χ describing excited-state system dynamics. We thus
offer experimental access to this theoretical formalism. This work
serves as a starting point for the reader to understand ultrafast laser
experiments in molecular systems and to gain a novel perspective of
nonlinear spectroscopy based on quantum information theory.
