High repetition pump-and-probe photoemission spectroscopy based on a compact fiber laser system

TL;DR

This paper presents a high repetition rate fiber laser-based TRPES system that achieves high signal-to-noise ratios and low pump fluence measurements, improving ultrafast electronic dynamics studies.

Contribution

It introduces a compact 95-MHz fiber laser system for TRPES, reducing space-charge effects and enabling low-fluence ultrafast measurements compared to traditional systems.

Findings

Achieved TRPES with 11.3 meV energy and 310 fs time resolution.

Demonstrated TRPES on bismuth at pump fluence as low as 30 nJ/mm².

Showed reduced space-charge broadening with the 95-MHz laser system.

Abstract

The paper describes a time-resolved photoemission (TRPES) apparatus equipped with a Yb-doped fiber laser system delivering 1.2-eV pump and 5.9-eV probe pulses at the repetition rate of 95 MHz. Time and energy resolutions are 11.3 meV and ~310 fs, respectively; the latter is estimated by performing TRPES on a highly oriented pyrolytic graphite (HOPG). The high repetition rate is suited for achieving high signal-to-noise ratio in TRPES spectra, thereby facilitating investigations of ultrafast electronic dynamics in the low pump fluence (p) region. TRPES of polycrystalline bismuth (Bi) at p as low as 30 nJ/mm2 is demonstrated. The laser source is compact and is docked to an existing TRPES apparatus based on a 250-kHz Ti:sapphire laser system. The 95-MHz system is less prone to space-charge broadening effects compared to the 250-kHz system, which we explicitly show in a systematic probe-power dependency of the Fermi cutoff of polycrystalline gold. We also describe that the TRPES response of an oriented Bi(111)/HOPG sample is useful for fine-tuning the spatial overlap of the pump and probe beams even when p is as low as 30 nJ/mm2.