A SIMPLIFIED METHOD FOR ABSOLUTE MPI CROSS-SECTION MEASUREMENTS - APPLICATION TO 3-PHOTON NONRESONANT IONIZATION OF XE AT 266NM

A simple method to measure absolute MPI cross sections based on a direct measurement of the ions, produced out of the focal region, is described. The method avoids the problem of the complicated effective-volume evaluation at the focus of a laser beam, difficulties in estimation of the absolute number of ions, as well as the problems arising due to measurements in the saturation regime. The method is best for high cross-section measurements; however, in order to demonstrate its feasibility, it has been applied to the study of non-resonant MPI of Xe. This three-photon ionization cross section, measured for the first time at the fourth harmonic of a mode-locked Nd:YAG laser (266 nm), is found to be (1.1 +/- 0.6) x 10(-82) cm6 s2.