Evaluation of optical probe signals from nonequilibrium systems

TL;DR

This paper predicts how nonequilibrium systems respond optically, revealing phase-dependent effects and resonances that enable control over signals based on initial quantum states and external driving fields.

Contribution

It introduces new theoretical insights into the phase dependence of optical responses in nonequilibrium systems, including effects of initial coherences and external field influences.

Findings

Linear response depends on electric field phase even without coherences

Quantum coherences induce additional phase-dependent resonances

External field frequency affects probe absorption in driven systems

Abstract

We predict several effects associated with the optical response of systems prepared in a nonequilibrium state by impulsive optical excitations. The linear response depends on the phase of the electric field even if the initial nonequilirbium state has only populations, no coherences. Initial quantum coherences induce additional phase dependence which also shows new resonances in nonlinear wave mixing. In systems strongly driven by an external optical field, the field frequency generates a phase dependent probe absorption. This gives further control to manipulate the relative contribution to the linear signal due to initial populations and coherences.