Expanding the momentum field of view in angle-resolved photoemission systems with hemispherical analyzers

TL;DR

This paper introduces a bias voltage method to expand the momentum field of view in angle-resolved photoemission systems with hemispherical analyzers, enabling better exploration of electronic structures at low photon energies.

Contribution

The authors develop an analytic model and experimental technique to increase the effective solid angle in photoelectron measurements using a bias voltage, enhancing laser-based photoemission capabilities.

Findings

Validated the model with TbTe3 data

Achieved larger momentum space coverage

Enhanced flexibility of photoemission setups

Abstract

In photoelectron spectroscopy, the measured electron momentum range is intrinsically related to the excitation photon energy. Low photon energies $<10$ eV are commonly encountered in laser-based photoemission and lead to a momentum range that is smaller than the Brillouin zones of most materials. This can become a limiting factor when studying condensed matter with laser-based photoemission. An additional restriction is introduced by widely used hemispherical analyzers that record only electrons photoemitted in a solid angle set by the aperture size at the analyzer entrance. Here, we present an upgrade to increase the effective solid angle that is measured with a hemispherical analyzer. We achieve this by accelerating the photoelectrons towards the analyzer with an electric field that is generated by a bias voltage on the sample. Our experimental geometry is comparable to a parallel plate capacitor and, therefore, we approximate the electric field to be uniform along the photoelectron trajectory. With this assumption, we developed an analytic, parameter-free model that relates the measured angles to the electron momenta in the solid and verify its validity by comparing with experimental results on the charge density wave material TbTe$_3$. By providing a larger field of view in momentum space, our approach using a bias potential considerably expands the flexibility of laser-based photoemission setups.