Photoemission electron microscopy for nanoscale imaging and attosecond control of light-matter interaction at metal surfaces

Electron dynamics at solid surfaces unfold on the nanometer length and attosecond timescale when driven by electromagnetic fields at optical frequencies, enabling vast scientific and technological applications in the field of nano-optics and nanoplasmonics. Direct imaging of the electrons upon interaction with light is a highly desirable tool for understanding and control of the dynamics, which requires ultrahigh spatiotemporal resolution. This thesis explores the combination of photoemission electron microscopy (PEEM) with few-cycle femtosecond laser pulses and attosecond extreme ultraviolet (XUV) pulses for studying ultrafast electron dynamics from metallic surfaces and nanosystems. The work involves development and implementation of new experimental tools including detection, data acquisition and analysis techniques for PEEM measurements. The first approach is using a combination of PEEM with attosecond streaking spectroscopy (atto-PEEM) for direct, non-invasive probing of nanoplasmonic fields from supported nanostructures. As a first step towards the implementation of the atto-PEEM concept, PEEM imaging on lithographically fabricated gold structures employing 93 eV attosecond XUV pulses from a 1 kHz high-harmonic generation (HHG) source is performed. The spatial resolution is limited to ~200 nm due to space charge effects when working with such a low-repetition-rate HHG source and chromatic aberrations caused by the large energy bandwidth of XUV-generated photoelectrons. Nevertheless, we show that microspectroscopic imaging of core-level and valence band electrons is achievable using our energy-resolved PEEM despite the aforementioned issues. Most importantly, we find that the fast photoelectrons from the valence band, which carry the attosecond temporal structure of the plasmonic field, are not affected by space charge effects. The currently developed megahertz-repetition-rate attosecond XUV sources are therefore expected to enable the experimental realization of nanoplasmonic streaking with ultrahigh spatiotemporal resolution in the near future. Second, PEEM is coupled with a single-shot stereographic above-threshold ionization phase meter, which allows carrier-envelope phase (CEP) tagging for studying attosecond control of photoemission. First experiments performed on gold nanospheres on a gold plane and on a random rough gold surface using few-cycle near-infrared pulses show a CEP artefact with a modulation period of π. The artefact is found to be caused by a laser intensity dependence of both the photoelectron spectra and the CEP measurement. Intensity tagging is therefore added to the current CEP tagging technique to correct this intensity-dependent artefact. As a result, a very weak CEP modulation (~1% amplitude) of the photoemission yield from a bulk tungsten surface with a 2π modulation period (as expected from solids) is successfully detected in the above-threshold photoemission regime after applying appropriate corrections based on the intensity tagging. Entering the tunneling regime, the CEP modulation increases to ~7% despite the presence of space charge effects due to high laser peak intensity. We also apply this technique to investigate the CEP dependence on gold nanotriangles and find no apparent CEP modulation within an accuracy of ~0.6% as given by our experimental conditions, which constitutes an upper limit for a possible CEP modulation from this nanostructure.