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 ${\mathrm{Nd}}^{3+}$: glass laser producing an electric field of $E=8\mathrm{}\times {10}^7$ V/cm. In the range 10 585 Å to 10 605 Å, two resonances have been found, shifted towards the high-energy side from the nearest states $5d{\left[\frac{1}{2}\right]}_1$ and $4d^{\prime }{\left[\frac{5}{2}\right]}_3$ by 39.5 ${\mathrm{cm}}^{-1\mathrm{}}$ and 42 ${\mathrm{cm}}^{-1\mathrm{}}$, respectively. Far from resonances, the dependence of the ionization rate on the laser intensity agrees with the lowest-order perturbation-theory prediction.