Non-perturbative up-conversion techniques: Ultrafast meets X-rays.” In Ultrafast Dynamics of Quantum Systems: Physical Processes and Spectroscopic Techniques, , Pp. 611–623. Plenum Press. Publisher's VersionAbstract. 1999. “
Femtosecond laser pulses are now available from the ultraviolet (200 nm) all the way to the mid-infrared (12 m) in compact (often commercially available) systems. This tunability is achieved through perturbative nonlinear optical wavelength conversion techniques in crystals. To reach further into the ultraviolet and Xray regions of the spectrum, a new set of techniques becomes necessary. In this paper, we will review some of these nonperturbative nonlinear optical methods. Specifically, we will consider the high harmonic generation process in detail, and go through the essentials of the semi-classical theory. Next, we will review a new technique, based on Thomson scattering, which has produced 0.4-Angstrom, 300-fs radiation. Finally we will consider means of measuring femtosecond pulses in this short wavelength regime.