Laser-based apparatus for extended ultraviolet femtosecond time-resolved photoemission spectroscopy

Abstract

A novel laser-based apparatus is presented utilizing high harmonic radiation for visible pump–EUV probe experiments on ultrafast processes. True femtosecond temporal resolution is achieved by a monochromator making use of dedicated narrowband multilayer mirrors rather than gratings for selection of single harmonic orders in the photon energy range between 66 and 73 eV. First applications of this new light source for electron spectroscopy on gas phase helium and xenon demonstrate the selection of a single high harmonic order with the intensity ratio between the selected and its adjacent harmonic not exceeding 10:1. A pump–probe study of hot electron production on a solid Pt(110) surface yields a cross-correlation corresponding to a temporal system resolution of 100 fs.

Femtosecond time-resolved photoelectron spectroscopy with a vacuum-ultraviolet photon source based on laser high-order harmonic generation

“…It facilitates extracting weak transient signals in time-resolved PES as small photoelectron intensities within plus or minus 3.1 eV of strong main lines can be readily detected without worrying about a structured background due to photoionization from partially suppressed adjacent harmonics. In contrast, single multilayer mirrors (61) or pairs of multilayer mirrors (63,66) were shown to transmit the adjacent harmonics with an intensity of the selected harmonic of 10% and more.…”

“…This comparably short pulse duration for monochromatized HHG VUV pulses makes our set up unique in a sense that, to the best of our knowledge, this is the shortest pulse duration measured so far with a monochromator based on a single grating. Shorter femtosecond pulses have been produced with pairs of multilayer optics (57,63,66) and pairs of gratings mounted in conical diffraction (55,56). Compared to other set ups based on conventional diffraction gratings (60) we produce shorter pulses because the grazing angle on the grating is comparably large and the distance of the HHG source to the grating is very short.…”

“…For ultrafast applications, time-resolved photoelectron spectroscopy (PES) (41) with pump-probe schemes where the sample is pumped with a laser pulse and probed with HHG pulses at a defined pump-probe delay has emerged as a powerful tool for the investigation of ultrafast dynamics in gas phase samples (42)(43)(44)(45)(46)(47) and on surfaces (48)(49)(50)(51)(52)(53)(54). A variety of set ups has been described to perform such experiments on gas phase samples (55)(56)(57)(58)(59)(60), on surfaces (61-64) or on both (65,66).…”

Large-scale homogeneous molecular templates for femtosecond time-resolved studies of the guest–host interaction

“…The pump-probe technique has proven to be the essential tool for femtochemistry (Zewail, 1994), where the dynamics of photoreactions is followed in the time domain. However, in contrast to the usual visible-or UV-probe utilized in tradi-tional femtochemistry, we intend to use probe pulses in the soft X-ray range thus establishing time-resolved X-ray photoelectron spectroscopy (XPS) (Haight and Peale, 1994;Siffalovic et al, 2001;Drescher et al, 2002a) for studies of intermolecular dynamics. XPS, also termed as electron spectroscopy for chemical analysis (ESCA), is a well-established technique for determining (yet hitherto in a static manner) the elemental composition of a molecule as well as the chemical environment of its atomic constituents (Siegbahn, 1967).…”

Oscillator-based High-order Harmonic Generation at 4MHz for Applications in Time-of-Flight Photoemission Spectroscopy

“…As a consequence, the statistics of measurements are limited to a few thousand events per second and a long acquisition time is required for applications in photoelectron-based spectroscopy and microscopy [4][5][6][7] (Fig. 1).…”