This chapter is devoted to the study of harmonic generation in atoms and the physics of attosecond pulses, also called attophysics, which are two major topics in the study of high-intensity laser–atom interactions. We start in Section 9.1 by reviewing important experiments, with particular emphasis on high-order harmonic generation, which is a very interesting probe of the behavior of atoms interacting with intense laser fields. In Section 9.2, we discuss harmonic generation calculations, first at the microscopic (single-atom response) level and then at the macroscopic level. The main properties of harmonics and some of their applications are discussed in Section 9.3. Finally, in Section 9.4, we examine how attosecond pulses can be produced and used to investigate the dynamics of atoms at unprecedented time and space scales. Reviews of harmonic generation have been given by L'Huillier, Schafer and Kulander [1], L'Huillier et al. [2], Joachain [3], Salières et al. [4], Protopapas, Keitel and Knight [5], Joachain, Dörr and Kylstra [6], Brabec and Krausz [7], Salières [8, 9] and Salières and Christov [10]. Attosecond physics has been reviewed by Agostini and DiMauro [11], Scrinzi et al. [12], Kienberger et al. [13], Niikura and Corkum [14], Krausz and Ivanov [15], Lewenstein and L'Huillier [16] and Scrinzi and Muller [17].

Experiments

In this section, we give an overview of key experiments which have been performed in the field of harmonic generation and the production of attosecond pulses.