Ions generation by multiphoton ionization in the focal space of a gaussian beam

When light intensities are distributed on a spherical wave according to a gaussian law, it is possible to obtain an accurate analytic relationship expressing the Ni number of ions created in a K-photon ionization experiment. This relationship may be considered, for a given K value, as a function of p = A int T0 ΓK0 dt which is called ionization probability at the center of curvature of the wave. It has been numerically computed with K = 2 through 7, 11 and 19. At last, it is shown how to get out of experimental results the value of A with the help of the graphs Ni(p, K).