Interpreting pulse-shape effects in pump-probe spectroscopies

TL;DR

This paper investigates how pulse-shape influences pump-probe spectroscopic measurements in a model of noninteracting fermions, revealing effects on density of states, photoelectron spectra, and Raman signals that are crucial for experimental interpretation.

Contribution

It provides a detailed analysis of pulse-shape effects on various spectroscopic signals in a noninteracting fermion model, highlighting the importance of probe-pulse width in data interpretation.

Findings

Probe-modified density of states follows pump evolution with sidebands.

Photoelectron spectra are affected by nonequilibrium occupations.

Raman cross section peaks are influenced by interference and stress tensor variations.

Abstract

The effect of the pulse-shape on pump-probe spectroscopies is examined for the simplest model of noninteracting fermions on an infinite-dimensional hypercubic lattice. The probe-modified density of states follows the time evolution of the pump and displays narrowing and Floquet-like sidebands at the pump maximum, whereas the photoelectron spectra are also strongly affected by the nonequilibrium occupation of the single-particle states due to the excitation from the pump. The nonequilibrium Raman cross section is derived, and the nonresonant one in both the $A_{1\mathrm{g}}$ and $B_{1\mathrm{g}}$ symmetries contains a number of peaks at the pump maximum, which can be attributed to an interference effect or Brillouin scattering off the time variations of the stress tensor. Both the "measured" occupation of single-particle states and the ratio of Stokes to anti-Stokes peaks are strongly modified by the probe-pulse width, which must be included in the interpretation of experimental results.