Dynamical alignment

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 dynamics of strongly-driven electrons on ultrafast timescales also lies at the basis of several phenomena in molecules. Among these, we have investigated dynamic alignment [26] and enhanced ionization in Coulomb explosions [27]. 

While the possibility to dynamically align molecules has become firmly established in the last few years, the electronic origin of the alignment force has not been directly observed yet. Quantum mechanically we understand the... 

Ovcharenko, I., Loots, G. G Hardison, R. C., Miller, W., and Stubbs, L. (2004) zPicture dynamic alignment and visualization tool for analyzing conservation profiles. Genome Res. 14, 472-477. 

The automatic beam alignment system was found to perform well, being capable of aligning the beam within minutes. A system was shown earlier by the same group (Ebert et al. 2000) to enable continuous dynamic alignment control. 

In very high resolution spectrometers, such as the dynamic alignment spectrometer mentioned above, three laser beams are run in parallel to the infrared beam. These three laser beams are positioned at the apices of an equilateral triangle. Laser fringe measurements are taken on all three beams and any error, (that is, if all the zero crossings are not simultaneous) is corrected by tilting the fixed mirror. By this method, both mirror tilt and sampling frequency measurement are accomplished. 

Figure 5.10. Path of three parallel laser beams through a dynamically aligned Michelson interferometer. The beams are detected by three separate detectors, and the signals from the detector are fed to three actuators that control the alignment of one of the minors. (Reproduced from [5], by permission of John Wiley Sons, Ltd. copyright 2002.)...

In both the continuous-scan and step-scan spectrometers, the extremely precise positioning of the movable mirror is ensured by adopting an efficient feedback mechanism such as the above-mentioned dynamic alignment. Further, some spectrometers are constructed so as to isolate the interferometer base from shocks, including earthquakes. It should be kept in mind that, even if such spectrometers are in use, shocks, vibrations, and tilts given inadvertently to the spectrometer may still have an adverse effect on the results of measurements. 

---