Parametric Projection Operator Technique for Second Order Non-linear Response

TL;DR

This paper introduces a parametric projector operator technique to calculate second order non-linear optical responses, deriving a quantum master equation that accounts for pulse delay effects in multilevel molecular systems.

Contribution

It presents a novel parametric quantum master equation incorporating pulse delay dependence for second order non-linear optical response calculations.

Findings

Distinct dynamics of excited state populations for different delays

Electronic coherence varies with pulse delay

Environmental effects influence system dynamics

Abstract

We demonstrate the application of the recently introduced parametric projector operator technique to a calculation of the second order non-linear optical response of a multilevel molecular system. We derive a parametric quantum master equation (QME) for the time evolution of the excited state of an excitonic system after excitation by the first two pulses in the usual spectroscopic four-wave-mixing scheme. This master equation differs from the usual QME by a correction term which depends on the delay \tau between the pulses. In the presence of environmental degrees of freedom with finite bath correlation time and in the presence of intramolecular vibrations we find distinct dynamics of both the excite state populations and the electronic coherence for different delays \tau.