Lasers attosecond

In ultrafast laser science the emergence of attosecond laser pulses raises the prospect of studying electronic wavepacket motion on the natural timescales of this motion in nature, namely the atomic unit of time (1 a.u. = 24 attosec-onds = 0.024 femtoseconds) [1,2]. Attosecond science may have a profound impact on the way we understand photo-induced physical and chemical processes. 

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. 

Photoionization in Optical Fields The Generation and Characterization of Attosecond Laser Pulses... 

The generation of attosecond laser pulses in high-harmonic generation is a natural consequence of the physics discussed in Sects. 3.2 and 3.3. As discussed in Sect. 3.3, the ionization that launches the electron into the continuum is a highly non-linear phenomenon that will favor field maxima in the femtosecond driver laser. Following this ionization step, and in the spirit of the results presented in Sect. 3.2, the electrons will be accelerated by the oscillatory field of the laser and move along relatively well-defined trajectories that carry the electron back to the parent ion at well-defined times. Consequently, we expect the electron-parent ion recombination and the XUV production to occur only during a small portion of the optical cycle. 

On a different development, recently an extension of the ELF to the time-dependent density functional formalism has been presented.58 With the advent of attosecond laser pulses, the information of the time scale and temporal order of the different bond breaking or bond formation processes will be important, and this is the kind of information one can extract from the time-dependent version of the ELF. 

Photoionization can create a coherent superposition of electronic states and therefore initiates electronic dynamics in atoms and molecules. Experiments on the latter are particularly difficult to interpret as change in the nuclear geometry is also expected. Indeed, the equilibrium geometry of the ionized and neutral species are unlikely to be the same. Therefore, the initial electron dynamics, that may last up to a few femtoseconds, is then followed by the onset of nuclear dynamics [ 1 ]. Theoretical methods are needed to help understand the effects seen in attosecond laser experiments (see, e.g., the reviews of Kling [2] and Ivanov [3]). 

The time scale of valence electrons is typically of the order of 10 femtoseconds, while that of the inner shell is of course much faster and becomes close to the speed of light velocity for heavy atoms. Just as the femto-scale laser technology made a great contribution to the analyses of chemical dynamics of nuclear motions, the attosecond laser is anticipated to play the similar role for electron dynamics. 

Thermal Processes Using Attosecond Laser Pulses When Time Matters... 

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