Momentum transfer in the ponderomotive potential of near-infrared laser pulses leads to sizable energy shifts and electron-wavepacket squeezing in time-resolved ARPES

TL;DR

This study demonstrates how near-infrared laser pulses induce momentum transfer in the ponderomotive potential, causing energy shifts and electron-wavepacket squeezing observed through time-resolved ARPES, with implications for probing transient electronic states.

Contribution

It introduces a method to measure and simulate ponderomotive momentum transfer effects in ultrafast photoemission experiments, revealing new electron-energy modulation phenomena.

Findings

Observation of delay-dependent electron energy oscillations

Identification of electron-energy bunching effect

Accurate simulation and fitting of experimental data

Abstract

We observe momentum transfer in the ponderomotive potential of near-infrared (NIR) laser pulses in time- and angle-resolved photoemission spectroscopy (tr-ARPES) experiments with ultrashort extreme ultraviolet probe pulses. Acceleration of photoelectrons in the transient grating provided by an intense laser pulse reflected at a surface leads to delay-dependent oscillations of electric kinetic energies. Photon and electron momenta determine the oscillation frequency. We experimentally observe and theoretically simulate electron yield modulations driven by a novel electron-energy bunching effect. Measurement results are simulated and fitted with high accuracy. Complete reversion of the ponderomotive momentum transfer allows for retrieval of the undisturbed initial state and the transient band structure for overlapping pump and probe pulses.