Design and characterization of a magnetic bottle electron spectrometer for time-resolved extreme UV and X-ray photoemission spectroscopy of liquid microjets

Atanu Bhattacharya,Stephan Thürmer,Shutaro Karashima,Takuya Horio,Toshinori Suzuki,Naoya Kurahashi,Yoshihiro Ogi,Suet Yi Liu,Yo-ichi Yamamoto

doi:10.1063/4.0000107

Atanu Bhattacharya, Stephan Thürmer + Show 7 more

Open Access

https://doi.org/10.1063/4.0000107

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Abstract

We describe a magnetic bottle time-of-flight electron spectrometer designed for time-resolved photoemission spectroscopy of a liquid microjet using extreme UV and X-ray radiation. The spectrometer can be easily reconfigured depending on experimental requirements and the energy range of interest. To improve the energy resolution at high electron kinetic energy, a retarding potential can be applied either via a stack of electrodes or retarding mesh grids, and a flight-tube extension can be attached to increase the flight time. A gated electron detector was developed to reject intense parasitic signal from light scattered off the surface of the cylindrically shaped liquid microjet. This detector features a two-stage multiplication with a microchannel plate plus a fast-response scintillator followed by an image-intensified photon detector. The performance of the spectrometer was tested at SPring-8 and SACLA, and time-resolved photoelectron spectra were measured for an ultrafast charge transfer to solvent reaction in an aqueous NaI solution with a 200 nm UV pump pulses from a table-top ultrafast laser and the 5.5 keV hard X-ray probe pulses from SACLA.

Highlights

A magnetic bottle time-of-flight (MBTOF) spectrometer is, despite its very simple design,1 a highly capable device for photoemission (PE) spectroscopy, featuring extremely high electron collection efficiency and simultaneous detection of the full spectral energy range on a per-shot basis
We describe a magnetic bottle time-of-flight electron spectrometer designed for time-resolved photoemission spectroscopy of a liquid microjet using extreme UV and X-ray radiation
While several designs of MBTOF spectrometers for ultrafast laser pump-probe PE spectroscopy of a liquid microjet have been reported,2–5 some specific design considerations are required for employing a MBTOF spectrometer in similar experiments using an X-ray free electron laser (XFEL)

Summary

INTRODUCTION

A magnetic bottle time-of-flight (MBTOF) spectrometer is, despite its very simple design, a highly capable device for photoemission (PE) spectroscopy, featuring extremely high electron collection efficiency and simultaneous detection of the full spectral energy range on a per-shot basis. These advantages make the spectrometer a preferable choice over a classical hemispherical electron energy analyzer (HEA) for ultrafast pump-probe photoemission spectroscopy with pulsed light sources. The magnetic field gradient is insufficient for full parallelization of high-energy electrons, so that a bundle of electron trajectories exhibit focusing and defocusing in a wavy pattern along the flight axis in the field-free drift region. When we measure slow electrons near zero kinetic energy, we apply at least þ0.5 V to the flight tube to increase the electron pass energy through the spectrometer and ensure an uniform detection sensitivity

Chamber

Electrostatic lens

Retarding mesh

Gated electron detector

Alignment

Estimation of energy resolution

X-ray photoelectron spectra

UV pump and hard X-ray probe experiment

CONCLUSION