CONTROLLING THE BRANCHING RATIO OF PHOTOIONIZATION PRODUCTS UNDER 2-COLOR EXCITATION - COMPETITION BETWEEN AC STARK SPLITTING AND 2-PATH INTERFERENCE

We investigate the variation of the photoionization yields into differ ent ionic channels by means of the one-photon-near-resonant two-photon ionization scheme under two-color excitation. We present a general fo rmulation and the results of specific calculations pertaining to the C a atom with realistic parameters. A significant change of the ionizati on into Ca+ 4s, 3d, and 4p channels has been observed as a detuning is varied, which agrees qualitatively well with the observation by Wang, Chen, and Elliott [Phys. Rev. Lett. 77, 2416 (1996)] for the Ba atom. The importance of the laser intensity effects is also addressed.