Resonant Multiphoton Ionization of Krypton with a Single-Mode Laser

Multiphoton ionization of krypton has been experimentally investigated for the first time with a single-mode tunable Nd³⁺: glass laser producing an electric field of E=8×10⁷ V/cm. In the range 10 585 {} to 10 605 {}, two resonances have been found, shifted towards the high-energy side from the nearest states 5d[1/2]₁ and 4d^'[5/2]₃ by 39.5 cm^-1 and 42 cm^-1, respectively. Far from resonances, the dependence of the ionization rate on the laser intensity agrees with the lowest-order perturbation-theory prediction.