Theory of pump-probe spectroscopy using an amplitude approach

P. R. Berman

Chunyuan Bai, Chun Huang, Zhongyao Yue +4 more

Transient absorption spectroscopy (TAS) conventionally employs a weak probe pulse to passively interrogate pump-induced coherences in a quantum system. Here, we demonstrate a distinct regime in which an intense probe pulse actively controls and interrogates quantum coherences. Using time-dependent perturbation theory, we derive an analytical expression for the absorption cross section that incorporates probe-induced Rabi and Raman effects. Consequently, the system response becomes explicitly probe-intensity dependent, leading to pronounced modifications of both the absorption amplitude and phase. These features are in excellent agreement with density-matrix calculations. We further validate the theory experimentally using TAS of atomic rubidium, where systematic variations of the probe intensity and pump-probe delay directly reveal these predicted features. Our results establish intense probe pulses as a direct and effective tool for manipulating quantum coherences without auxiliary control fields.

James K. Freericks, O. P. Matveev, Andrij M. Shvaika +1 more

We present a theoretical description of time-resolved photoemission in charge-density-wave insulators that derive their ordering from electron nesting effects. In these pump/probe experiments, a large amplitude (but short duration) pump pulse excites the system into nonequilibrium and then a higher frequency low amplitude probe pulse photoexcites electrons, which are measured at the detector. We describe effects of electron correlations on the photoelectron spectroscopy and provide details for the theoretical techniques used to solve these problems. We also show how the gap fills in as the system is excited, even though the order parameter does not go to zero. The theory is developed for the Falicov-Kimball model, which can be solved exactly with nonequilibrium dynamical mean-field theory.

P. R. Berman, B. Dubetsky, Jingzhong Guo

V. L. Jacobs

G. Khitrova

This thesis presents theoretical calculations relating to pump-probe and four-wave mixing spectroscopy. In pump-probe spectroscopy, one measures the absorption profile for the situation when an arbitrarily strong pump field drives a given atomic transition and a weak probe field drives the same transition. We have carried out calculations of probe absorption in vapors for arbitrary ratios of natural width and detuning to the Doppler width associated with a given transition. New line shape features which were absent in previous theories are observed.