Attosecond time-resolved

We illustrate the use of multichannel single-ionization scattering states for the interpretation of time-resolved experiments in the case of the attosecond-XUV-pump IR-probe attosecond interferometric spectroscopy of the doubly... 

In the second part, we discuss possible applications of attosecond laser pulses to future studies of time-resolved electron dynamics in strongly driven systems. We discuss our current understanding of the time-dependent behaviour of non-perturbatively driven electrons in atoms, molecules and clusters. In Sect. 3.4 we discuss differences that arise when the generation of attosecond pulses is performed in different atomic media. This is followed in Sect. 3.5 by a description of the role of electron dynamics in dynamical alignment and enhanced ionization of molecules. Finally, in Sect. 3.6 the role of electron dynamics in laser heating of large clusters is discussed. 

The pump-probe pulses are obtained by splitting a femtosecond pulse into two equal pulses for one-color experiments, or by frequency converting a part of the output to the ultraviolet region for bichromatic measurements. The relative time delay of the two pulses is adjusted by a computer-controlled stepping motor. Petek and coworkers have developed interferometric time-resolved 2PPE spectroscopy in which the delay time of the pulses is controlled by a piezo stage with a resolution of 50 attoseconds [14]. This set-up made it possible to probe decoherence times of electronic excitations at solid surfaces. 

The second volume of Laser Spectroscopy covers the different experimental techniques, necessary for the sensitive detection of small concentrations of atoms or molecules, for Doppler-free spectroscopy, laser-Raman-spectroscopy, doubleresonance techniques, multi-photon spectroscopy, coherent spectroscopy and time-resolved spectroscopy. In these fields the progress of the development of new techniques and improved experimental equipment is remarkable. Many new ideas have enabled spectroscopists to tackle problems which could not be solved before. Examples are the direct measurements of absolute frequencies and phases of optical waves with frequency combs, or time resolution within the attosecond range based on higher harmonics of visible femtosecond lasers. The development of femtosecond non-collinear optical parametric amplifiers (NOPA) has considerably improved time-resolved measurements of fast dynamical processes in excited molecules and has been essential for detailed investigations of important processes, such as the visual process in the retina of the eye or the photosynthesis in chlorophyl molecules. 

Attosecond dynamics is now one of the most active fields in science [222, 476] (see also the introductory section of Ref. [499], which shows a concise list of the studies covering many phenomena and relevant studies). In particular, tracking electronic motions in chemical dynamics is a fundamentally important process. To monitor those electron wavepacket dynamics in an attosecond intense laser field [476], Bandrauk and his coworkers have developed the theory of attosecond-scale time-resolved photoelectron spectroscopy [499, 500], Photoionization dynamics of small molecules like has been studied so far, for which direct numerical integrations of the related (low-dimensional) time-dependent Schrodinger equations are possible. The photoelectron signals are extracted from those numerical solutions... 

The development of ultrashort laser pulses and of new detection techniques that allow a very high time resolution has brought about impressive progress in the study of fast processes. The achievable time resolution has been pushed recently into the attosecond range (1 as = 10 s). Spectroscopists can now quantitatively follow up ultrafast processes, which could not be resolved ten years ago. 

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