Attosecond Angle-Resolved Photoelectron Spectroscopy

Abstract

We report experiments on the characterization of a train of attosecond pulses obtained by highharmonic generation, using mixed-color (XUV IR) atomic two-photon ionization and electron detection on a velocity map imaging detector. We demonstrate that the relative phase of the harmonics is encoded both in the photoelectron yield and the angular distribution as a function of XUV-IR time delay, thus making the technique suitable for the detection of single attosecond pulses. The timing of the attosecond pulse with respect to the field oscillation of the driving laser critically depends on the target gas used to generate the harmonics. DOI: 10.1103/PhysRevLett.91.223902 PACS numbers: 42.65.Ky, 32.80.Rm, 42.65.Re The development of ultrashort laser pulses has led to significant advances in physics, chemistry, and biology. With femtosecond lasers the elementary motions of atoms and molecules can be observed [1], leading, for example, to a better understanding of complex biological systems [2]. Although electron dynamics often plays a crucial role in these systems, experimental studies have thus far been mostly limited to investigating the ''slow'' particles (i.e., atoms) that move under the influence of the intramolecular potentials. In order to investigate electron dynamics in real time, pulse durations have to enter the subfemtosecond (also known as attosecond, 1 as 1 10 ÿ18 s) domain [3]. Important advances have been made in the experimental realization and detection of attosecond laser pulses [4 -6] formed through the generation of high-order harmonics of femtosecond infrared (IR) laser pulses in noble gas atoms. In that process, attosecond time structure results from phase locking of a series of discrete harmonics [5,7,8] or a sufficiently broad segment of the harmonics continuum [6]. In this work, the time structure of such attosecond pulses is characterized from the angular distribution of the photoelectrons they produce in atomic mixed-color two-photon ionization.Many problems still have to be solved before well characterized and controlled attosecond pulses can be used as a routine tool for time-resolved spectroscopy [3,9]. When many-cycle IR pulses are used for the harmonic generation, the attosecond pulses appear in a pulse train, which is incompatible with most pump-probe experiments. Therefore the ultimate goal is to produce a single attosecond pulse. Another problem is the characterization of attosecond pulses. Full characterization can be done only through a nonlinear process, since linear processes do not mix different frequency components A q cos ! q t ' q and thus are insensitive to their relative phase ' q ÿ ' q 0 . Knowledge of the latter is essential and (together with the easily measurable amplitudes A q ) sufficient for determining a complete field reconstruction P A q exp i w q t ' q except for an overall phase. Thus far, mixed-color multiphoton ionization involving one extreme ultraviolet (XUV) and one or more fundamental photons has been the only process delivering enough signal to allow ...

Ultrafast electronic spectroscopy for chemical analysis near liquid water interfaces: concepts and applications

“…For photoelectron spectroscopy and XPS this is not necessary. High harmonics are also the basis of attosecond pulses and thus of the field of attosecond physics [19,[22][23][24][25][26][27][28][29][30][31][32].…”

Attosecond electron wave packet interferometry

“…The key results of this work are presented in Fig. 3b,c, where two-dimensional cuts through the three-dimensional momentum distributions 19,20 obtained in argon using a velocity-map imaging technique 21,22 are presented for two delays between the XUV and IR fields. The distributions are more complex than those presented in helium.…”

Attosecond pulse walk-off in high-order harmonic generation

“…These experiments demand high interferometric stability, on the order of tens of attoseconds, and require control of the timing of the attosecond pulses relative to the fundamental field. In some early implementations of the RABITT scheme [5,7,8], the probe pulse and the generation pulse were both propagated through the generation medium, making it possible to encode the phase relation between the generating and the probing field into the recorded electron spectrogram, but at the same time perturbing the regularity of the pulse train.In this work, we perform RABITT measurements using an actively stabilized interferometer. We present an experimental study of the group delay of the attosecond pulses relative to the generating field as a function of the gas density in the generation cell.…”