Self-Analysis of Coherent Oscillations in Time-Resolved Optical Signals

The specific origin of oscillations in time-resolved optical signals, in particular, for complex systems with nontrivial interstate couplings and nonseparable electron-nuclear motion, is often difficult to assign. Here, we show that coherent oscillations in two-dimensional photon-echo are capable of self-analysis; their beating maps provide a tool to tell apart ground-state bleach (GSB), stimulated emission (SE), and excited-state absorption (ESA) contributions to the oscillatory signal component. Because GSB carries information on ground-state coherence while SE and ESA reflect the excited-state coherence, the observed oscillations can be unambiguously assigned to ground-state or excited-state coherent motion. The findings prove especially advantageous for systems with dense detectable manifolds of states pertaining to each electronic state. An analogous analysis for frequency-resolved (dispersed) pump-probe spectroscopy is discussed briefly.