MODULATION EFFECT OF A SPATIAL BEAM PROFILE ON SINGLE-COLOR RESONANT 2-STEP 3-PHOTON IONIZATION

The ionization signals and the dynamic Stark shifts in a single-colour resonant two-step three-photon scheme are studied by using the Bloch equation. The modulation effects of the trabsverse and longitudinal pr ofiles of a Gaussian beam are examined. The intermediate level is chos en to be resonant within a few tens of GHz by a photon. The Rabi frequ encies for the uniform beam are taken to be within 10 GHz. The ionizat ion signal and the dynamic Stark shift are found to be enhanced due to the localization effect of the Gaussian profile in the transverse dir ection. It turns out that the height of the ionization signal is reduc ed, but the width is enhanced by the focussing of the Gaussian beam.