Abstract
How quanta of energy and charge are transported on both atomic spatial and ultrafast time scales is at the heart of modern technology. Recent progress in ultrafast spectroscopy has allowed us to directly study the dynamical response of an electronic system to interaction with an electromagnetic field. Here, we present energy-dependent photoemission delays from the noble metal surfaces Ag(111) and Au(111). An interferometric technique based on attosecond pulse trains is applied simultaneously in a gas phase and a solid state target to derive surface-specific photoemission delays. Experimental delays on the order of 100 as are in the same time range as those obtained from simulations. The strong variation of measured delays with excitation energy in Ag(111), which cannot be consistently explained invoking solely electron transport or initial state localization as supposed in previous work, indicates that final state effects play a key role in photoemission from solids.
Highlights
The beam is split into a probe branch (20%) that is sent through a delay line and a pump branch (80%), which produces attosecond pulse trains (20-45 eV, 300 as pulse width) by high-harmonic generation in Ar
Photoemission spectra from Ar gas are recorded at different delays between the two pulses
It should be noted that the phase, φ2q, could be retrieved by direct curve fitting without Fourier filtering
Summary
A Ti:sapphire based chirped-pulse amplification system provides ultrashort laser pulses (~25 fs, 1.2 mJ, central wavelength 796 nm) at 1 kHz repetition rate. Photoemission spectra from Ar gas are recorded at different delays between the two pulses (typical delay step = 250 as). The collection of these spectra constitutes the first RABBITT trace that was used for calibration purpose. A second toroidal mirror (incidence angle 80°) images the first focus onto a solid sample surface in a one-to-one geometry. Photoemission spectra from the metal surface are recorded with a hemispherical electron analyser. These spectra are measured simultaneously with the ones in Ar and form the second RABBITT trace. Both pulses are p-polarized and the angle of incidence on the surface is 75°
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