Attosecond spectroscopy

Attosecond Spectroscopy of Atomic Inner Shell Processes... 

While the electron wavefunction can be used to obtain the energy and other properties of the electron, the question arises, in quantum mechanics generally, as to what the wavefunction itself means . This has been, and still is, the subject of much debate and there is currently intense research activity into using attosecond spectroscopy to probe atomic wavefimctions [16]. The most useful interpretation of the wavefunction for chemistry is that due to Born, who, by analogy to a light wave, where the intensity is proportional to the square of the amplimde, suggested... 

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... 

J. Mauritsson, T. Remetter, M. Swoboda, K. Kliinder, A. L HuiUier, K.J. Schafer, et al., Attosecond electron spectroscopy using a novel interferometric pump-probe technique, Phys. Rev. Lett. 105 (2010) 053001. 

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. 

Ultrafast spectroscopy primarily employs optical techniques to study molecular motion in the femtosecond to attosecond range. 

Zewail. Ahmed H. Chemistry at the Uncertainty Limit. Angewandte Chemie International Edition 40 (2001) 4,371-75. This is a nonmath-ematical presentation of the relationship between femtosecond (10" s) spectroscopy [and even attosecond (10 s) spectroscopy] with the Heisenberg uncertainty principle. 

In Sect. 6.5, we show that attosecond jr-electron rotation can be identified by observing vibrational amplitudes with optical transient spectroscopy. 

Thus, information on attosecond jt-electron rotation can be obtained by detecting femtosecond molecular vibrations with spectroscopy, although this type of detection is not a direct imaging of ultrafast electron dynamics. 

Th. Schultz, M. VrakMng (eds.), Attosecond and XUV Spectroscopy Ultrafast Dynamics and Spectroscopy (Wiley/VCH, Weinheim, 2014)... 

R. Kienberger, F. Krausz, Sub-femtosecond XUV Pulses Attosecond Metrology and Spectroscopy. Topics Appl. Phys., vol. 95 (Springer, Berlin, 2004), p. 343... 

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. 

The time of excitation to the Franck-Condon state is approximately 1 fs (10 s). Thus, these techniques will freeze out any equilibrium that involves the actual movement of nuclei, such as a cis-trans interconversion. Electron exchange can, however, be faster than a vibration. These very fast electron transfer processes can be probed by exposing a sample to laser radiation with a pulse shorter than 10 s, i.e., the realms of femtosecond (10 s) and attosecond (10 s) spectroscopy. ... 

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... 

As a fundamental study on field induced chemical reactions, Neidel and Vrakking et al. observed attosecond d3mamics of electrons in a series of small- and medium sized neutral molecules by monitoring time-dependent variation of the parent molecular ion 3delds [296]. The information on electron dynamics was extracted from experimental data on the basis of the relation between the time dependent dipole and ionization. This was performed in the two-color femtosecond near infrared (NIR) pump-attosecond extreme ultraviolet (XUV) probe experiment. They claim that the time-dependent dipole induced by the moderately strong NIR pulse field is monitored with attosecond time resolution. The oscillations are interpreted in terms of a time dependent screening induced by the polarization of the molecule, which alters the photoionization yield of the neutral molecule. This scheme can be considered as the first example of molecular attosecond Stark spectroscopy. 

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