High-resolution vacuum-ultraviolet and ultraviolet photoionization spectroscopy of krypton

Accurate spectroscopy of krypton is performed on five transitions from the (4p 6 ) 1 S 0 ground state to the 5d[1/2] 1 , 6s[3/2] 1 , 5p[1/2] 0 , 5p[3/2] 2 and 5p[5/2] 2 excited states ( jl -coupling notation) by means of 1VUV + 1UV and 2UV + 1UV resonance-enhanced photoionization. Isotope shifts of all six stable isotopes are determined, and a King plot analysis indicates a large field shift factor even for transitions in which no s electron is involved. Absolute frequency calibration is performed on three transitions, leading to a novel determination of the excited state energies of Kr with an accuracy of ~0.0013 cm -1 . An accurate value for the ionization energy of 86 Kr, 112 914.516(14) cm -1 , is derived along with ionization energies for all even isotopes. The ac Stark effect on the two-photon transition to the 5p[1/2] 0 excited state is investigated. For light intensities up to ~260 MW cm -2 a linear shift of 0.75(48) Hz (W cm -2 ) -1 is observed, while at higher intensities the line exhibits a sub-linear shift and an asymmetric broadening. Consequences of the results obtained for the 5p[1/2] 0 state on resonance-enhanced narrow-band XUV/VUV generation are discussed.