Time-resolved Photoelectron Momentum Microscopy using a 1 MHz High-Harmonic Generation Beamline

In the last decades, high-harmonic generation (HHG) has rapidly developed from an experimental novelty into a workhorse of laboratory-based ultrafast physics research. In the field of photoelectron spectroscopy, extreme ultraviolet light from HHG is particularly interesting because it allows access to the electronic structure in the full Brillouin zone with femtosecond or even attosecond time-resolution. In this field, the development of HHG is mirrored by a similarly dramatic development of novel, advanced photoelectron detectors. As an example, the time-of-flight momentum microscope (MM) allows for the measurement of the full momentum vector and kinetic energy of each photoemitted electron. However, because the MM can only measure a single photoelectron per laser pulse, good measurement statistics demand for a high repetition rate light source – a requirement which is at odds with the usual need for high-energy laser pulses to drive the HHG process.