Atoms and electrons in intense laser fields (A photoionization study).

The behavior of atoms and electrons is modified by the presence of intense radiation fields. Atomic quantum levels shift and broaden, the ionization potential increases, and most significantly, atoms become unstable and ionize. The energy required for the ionization is taken from the laser field by means of absorbing photons. Since high laser intensities are usually achieved in the frequency range where the photon energy is smaller than the ionization energy, multiphoton processes dominate experimental results. At sufficiently high laser intensities, Above-Threshold Ionization occurs, where the number of absorbed photons exceeds the minimum number required for ionization. In this thesis, Above Threshold Ionization of atoms is examined experimentally and theoretically. The emphasis is placed on photoelectron spectra and angular distributions. Since free electrons are affected by intense laser light, it is important to consider the process of photoionization and subsequent photoelectron behavior separately. This motivated a very careful and detailed investigation of electron interaction with intense coherent radiation.