Abstract
AbstractAttosecond pulses, produced through high-order harmonic generation in gases, have been successfully used for observing ultrafast, subfemtosecond electron dynamics in atoms, molecules and solid state systems. Today’s typical attosecond sources, however, are often impaired by their low repetition rate and the resulting insufficient statistics, especially when the number of detectable events per shot is limited. This is the case for experiments, where several reaction products must be detected in coincidence, and for surface science applications where space charge effects compromise spectral and spatial resolution. In this work, we present an attosecond light source operating at 200 kHz, which opens up the exploration of phenomena previously inaccessible to attosecond interferometric and spectroscopic techniques. Key to our approach is the combination of a high-repetition rate, few-cycle laser source, a specially designed gas target for efficient high harmonic generation, a passively and actively stabilized pump-probe interferometer and an advanced 3D photoelectron/ion momentum detector. While most experiments in the field of attosecond science so far have been performed with either single attosecond pulses or long trains of pulses, we explore the hitherto mostly overlooked intermediate regime with short trains consisting of only a few attosecond pulses. We also present the first coincidence measurement of single-photon double-ionization of helium with full angular resolution, using an attosecond source. This opens up for future studies of the dynamic evolution of strongly correlated electrons.
Highlights
The advent of attosecond pulses in the beginning of the millennium [1, 2] enabled the study of fundamental lightmatter interactions with unprecedented time resolution [3], revealing subfemtosecond electron dynamics in atoms, molecules and solids, such as ionization time delays [4,5,6,7], the change of dielectric polarizability [8], and the timescale of electron correlations [9, 10].Attosecond pulses are generated through high-order harmonic generation (HHG), when intense femtosecond pulses are focused into a generation gas [11]
The process of HHG significantly changes from the case of multicycle, long driving pulses, where the attosecond pulses emitted from subsequent half-cycles are nearly identical except for a π-phase shift between them, to the case of few-cycle driving pulses, where attosecond pulses emitted from consecutive half-cycles can be very different from each other
This spectrometer is based on a revised Coincidences entre ions et electrons localises (CIEL) design [16], which is conceptually similar to reaction microscope or Cold Target Recoil Ion Momentum Spectroscopy [33, 34]
Summary
The advent of attosecond pulses in the beginning of the millennium [1, 2] enabled the study of fundamental lightmatter interactions with unprecedented time resolution [3], revealing subfemtosecond electron dynamics in atoms, molecules and solids, such as ionization time delays [4,5,6,7], the change of dielectric polarizability [8], and the timescale of electron correlations [9, 10]. We present a high-repetition rate, flexible attosecond light source, designed for the study of gas phase correlated electron dynamics, as well as timeresolved nanoscale imaging. This article both summarizes and extends the previous work [14, 15]. The paper is structured as follows: The first section introduces the optical setup by briefly discussing the laser source and the XUV-IR pump-probe interferometer, before examining the gas target design for HHG and the control of the emitted APTs and introducing the 3D photoelectron/ion spectrometer. We close by presenting measurements of the fully differential cross section for double ionization of helium, an experiment that to our best knowledge has not been performed with attosecond pulses before
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