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We present a simple electron time of flight spectrometer for time resolved photoelectron spectroscopy of liquid samples using a vacuum ultraviolet (VUV) source produced by high-harmonic generation. The field free spectrometer coupled with the time-preserving monochromator for the VUV at the Artemis facility of the Rutherford Appleton Laboratory achieves an energy resolution of 0.65 eV at 40 eV with a sub 100 fs temporal resolution. A key feature of the design is a differentially pumped drift tube allowing a microliquid jet to be aligned and started at ambient atmosphere while preserving a pressure of 10-1 mbar at the micro channel plate detector. The pumping requirements for photoelectron (PE) spectroscopy in vacuum are presented, while the instrument performance is demonstrated with PE spectra of salt solutions in water. The capability of the instrument for time resolved measurements is demonstrated by observing the ultrafast (50 fs) vibrational excitation of water leading to temporary proton transfer. [ABSTRACT FROM AUTHOR]

The laser-assisted photoelectric effect from liquid surfaces is reported for the first time. Photoelectrons generated by 35.6 eV radiation from a liquid microjet of water under vacuum are dressed with a ħ ω=1.55 eV laser field. The subsequent redistribution of the photoelectron energies consists in the appearance of sidebands shifted by energies equivalent to ħω, 2ħω, and 3ħω. The response has been modeled to the third order and combined with energy-resolved measurements. This result opens the possibility to investigate the dynamics at surfaces of liquid solutions and provide information about the electron emission process from a liquid. [ABSTRACT FROM AUTHOR]

We describe a complete technological system at Imperial College London for Attosecond Science studies. The system comprises a few-cycle, carrier envelope phase stabilized laser source which delivers sub 4 fs pulses to a vibration-isolated attosecond vacuum beamline. The beamline is used for the generation of isolated attosecond pulses in the extreme ultraviolet (XUV) at kilohertz repetition rates through laser-driven high harmonic generation in gas targets. The beamline incorporates: interferometers for producing pulse sequences for pump-probe studies; the facility to spectrally and spatially filter the harmonic radiation; an in-line spatially resolving XUV spectrometer; and a photoelectron spectroscopy chamber in which attosecond streaking is used to characterize the attosecond pulses. We discuss the technology and techniques behind the development of our complete system and summarize its performance. This versatile apparatus has enabled a number of new experimental investigations which we briefly describe. [ABSTRACT FROM AUTHOR]

The characterization of the temporal profile of plasmonic fields is important both from the fundamental point of view and for potential applications in ultrafast nanoplasmonics. It has been proposed by Stockman et al (2007 Nat. Photonics 1 539) that the plasmonic electric field can be directly measured by the attosecond streaking technique; however, streaking from nanoplasmonic fields differs from streaking in the gas phase because of the field localization on the nanoscale. To understand streaking in this new regime, we have performed numerical simulations of attosecond streaking from fields localized in nanoantennas. In this paper, we present simulated streaked spectra for realistic experimental conditions and discuss the plasmonic field reconstruction from these spectra. We show that under certain circumstances when spatial averaging is included, a robust electric field reconstruction is possible. [ABSTRACT FROM AUTHOR]

Symmetry breaking across phase transitions often causes changes in selection rules and emergence of optical modes which can be detected via spectroscopic techniques or generated coherently in pump-probe experiments. In second-order or weakly first-order transitions, fluctuations of the ordering field are present above the ordering temperature, giving rise to intriguing precursor phenomena, such as critical opalescence. Here, we demonstrate that in magnetite (Fe3O4) light excitation couples to the critical fluctuations of the charge order and coherently generates structural modes of the ordered phase above the critical temperature of the Verwey transition. Our findings are obtained by detecting coherent oscillations of the optical constants through ultrafast broadband spectroscopy and analyzing their dependence on temperature. To unveil the coupling between the structural modes and the electronic excitations, at the origin of the Verwey transition, we combine our results from pump-probe experiments with spontaneous Raman scattering data and theoretical calculations of both the phonon dispersion curves and the optical constants. Our methodology represents an effective tool to study the real-time dynamics of critical fluctuations across phase transitions. [ABSTRACT FROM AUTHOR]