Nonlinear spectroscopy
Conventional pump-probe spectroscopy can be understood as a sequence of two linear experiments - first the pump pulse excites the system and then the probe pulse tests the following dynamics via detecting changes in the absorption, bleach and stimulated emission signals. However, in order to obtain information about the time-scales within the pulse length or to understand echo-type of experiments, one has to use the machinery of nonlinear spectroscopy (see S. Mukamel, Nonlinear Optical Spectroscopy). Usually one applies density matrix theory which allows representing the various orders of experiment as a perturbation expansion in terms of the interaction with the field. The signal is expressed as a sum of all possible Liouville space pathways. The formalism has a nice and intuitive graphical representation via double-sided Feynman diagrams. The technique in combination with Redfield relaxation theory is a powerful method for analyzing coherent multidimensional spectroscopy experiments and is frequently used in our department.
Last update: 23 October 2006
