Third Harmonic Generation and Multiphoton Ionization Spectroscopy

Abstract

Nonlinear phenomena, such as multiphoton excitation (MPE) processes leading to ionization and third-harmonic generation (THG) in gases have become the issue of extensive studies over recent years. Studies in rare gases in particular have resulted in several interesting observations in this respect [1]. Thus, it has been established that three-photon resonantly enhanced multiphoton ionization (MPI) in the vicinity of states which are single photon optically coupled to the ground state may occur in efficient competition with THG. A characteristic example is the competition between the MPI and THG in xenon when tuning through the 6s 3/2 J=1 three-photon allowed intermediate state [1]. Several novel aspects related to these effects have been treated theoretically by Garrett et al. [2] and by Jackson and Wynne [3] in a series of papers. In these papers, the THG in the negatively dispersive side of three-photon resonances is treated quantitatively. Thus, the dependence of the wavelength range of the third-harmonic radiation profile on gas pressure, gas composition, and exciting beam intensity may be predicted with a high degree of accuracy.