High Intensity Molecular Multiphoton Ionization

Abstract

Multiphoton ionization (MPI) of molecules has been studied over a wide range of conditions which can be broadly divided into three general categories. First, resonantly-enhanced multiphoton ionization (REMPI) is accessible with moderate intensities (10⁹ - 10¹¹W/cm²)¹. REMPI generally employs one or more narrow band lasers to excite various zero-field resonances in the molecule. Much detailed spectroscopic information can be obtained with this technique. Second, REMPI can be extended to higher intensities (10¹¹ - 10¹³ W/cm²) with high-power short-pulse lasers. In this situation the potential curves responsible for the zero-field resonances begin to be affected by the intense laser field.² There is currently much interest in exactly how these potential curves are distorted by the strong laser field. Third, if there are no zero-field resonances in a molecule, MPI at high intensities still proceeds through resonance enhancement, although the resonances are entirely induced by the laser field, itself³.