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Ionization by an attosecond pulse launches an electron wave packet in the continuum which contains rich information about the pulse, the parent system, and the ionization dynamics. This emission process is not instantaneous in the sense that the electrons take a finite time to leave the potential. This time is closely related to the Wigner time. In this paper we introduce the stereo Wigner time delay, which measures the relative delay between electrons emitted to the left and right in an asymmetric system. We present a theoretical study of the delay in photoemission for a small asymmetric molecular system using the streaking technique. The stereo Wigner time delay shows advantages compared to previous schemes. Our numerical calculation shows that such a measurement removes the infrared laser-Coulomb coupling, which has been problematic in the interpretation of the measured delay in photoemission from atomic systems. © 2014 American Physical Society.

This thesis presents two sources of extreme ultraviolet (XUV) radiation based on high-order harmonic generation (HHG) in gases. The sources were developed for experiments requiring high-flux harmonic beams or HHG pulses at high-repetition rate. These were used experimentally to image nano-scale objects. The high-flux HHG source was used for digital in-line holography, and the high-repetition rate source for photoemission electron microscopy. In addition, a conceptual design for a high-flux gas beamline for a large scale facility, Extreme Light Infrastructure - Attosecond Light Pulse Source, is described. The work focuses on the construction and development of the driving laser systems and the HHG sources, as well as on the optimization of their performance. The thesis describes the two lasers used to drive the HHG sources: a high-power laser system and a newly built optical parametric chirped pulse amplification (OPCPA) system. The two systems are both based on the chirped pulse amplification technique, but the amplification process is carried out in different ways. The high-power laser system is based on linear amplification in Ti:Sapphire while the OPCPA system uses nonlinear amplification via difference frequency generation. Furthermore, the use of multi-color driving fields to manipulate the generation process, both from the microscopic and the macroscopic points of view, was investigated. The combination of the fundamental field with its second harmonic in a non-collinear geometry allows us to probe and control macroscopic properties. The addition of loworder odd harmonics in a collinear geometry results in an enhancement of the single atom response.

We extend the ideas of wave-packet interferometry to implement the algorithm of spectral phase interferometry for direct electric-field reconstruction (SPIDER) for characterizing the amplitude and phase of electron wave packets. Single-photon ionization by an attosecond pulse launches an electron wave packet in the continuum. Ionization by a train of two attosecond pulses in the presence of a moderate infrared pulse creates an interferogram in the final photoelectron momentum distribution. From the interferogram, the complex electron wave function can be reconstructed. If the pulses are well characterized, the amplitude and phase of the bound-free dipole matrix element can be reconstructed over a wide energy range. This is demonstrated by application of the retrieval method to momentum distributions obtained by numerical solution of the time-dependent Schrödinger equation. The case of Coulombic potentials requires appropriate treatment of the laser-Coulomb coupled dynamics. © 2013 American Physical Society.