Abstract

The question being asked is how the multiphoton ionization (MPI) signal (from a gaseous target) varies as a function of the focal length of the laser beam focusing lens. By decreasing the focal length (hence more tightly focusing), the light intensity is increased and thus the ionization probability. However, the effective focal volume for the nth-order process V_n is decreased. At intensities below saturation, a relationship between signal strength and the focal length of the lens can be deduced qualitatively as follows.

© 1986 Optical Society of America