3-PHOTON IONIZATION OF CA

The two-and three-photon resonant ionization of Ca has been studied. C alcium atoms in the thermal atomic beam were ionized from the ground 4 s(2) S-1(0) state by three-photon absorption. The ion signals exhibite d resonances attributed to the two-photon transition 4s(2) S-1(0)-4s6s S-1(0) and three-photon transitions due to 3d17f,...,3d22f P-1(1), 3d 19p,..., 3d24p P-1(1), 3d18f,...,3d19f P-3(1) and 3d23f, 3d25f D-3(1) autoionizing states. A simple theoretical model was used to reproduce the main features of the observed spectra due to the two-photon resona nt ionization.