# Coherent Excitonic Quantum Beats in Time-Resolved Photoemission Measurements

## TL;DR

This paper develops a theoretical framework to analyze coherent excitonic quantum beats observed in time-resolved photoemission spectroscopy, demonstrating how ultrafast laser pulses can coherently excite multiple exciton states and produce observable interference effects.

## Contribution

It introduces a formalism for calculating time- and angle-resolved photoemission spectra from coherently excited exciton states and applies it to a hydrogenic model to identify key control parameters.

## Key findings

- Quantum beats are most pronounced midway between exciton energy levels.
- The central energy of the pump pulse can tune the quantum beat effects.
- Coherent exciton excitation leads to observable interference in photoemission spectra.

## Abstract

Coherent excitation of materials via ultrafast laser pulses can have interesting, observable dynamics in time-resolved photoemission measurements. The broad spectral width of ultrafast pump pulses can coherently excite multiple exciton energy levels. When such coherently excited states are probed by means of photoemission spectroscopy, interference between the polarization of different exciton levels can lead to observable coherent exciton beats. Here, we present the theoretical formalism for evaluating the Time- and Angle- Resolved Photoemission Spectra (tr-ARPES) arising from the coherently excited exciton states. We subsequently apply our formalism to a simple model example of hydrogenic exciton energy levels to identify the dependencies that control the quantum beats. Our findings indicate that the most pronounced effect of coherent quantum excitonic beats is seen midway between the excited exciton energy levels and the central energy of the pump pulse provides tunability of this effect.