The even parity J = O , I and 2 autoionizing spectra of Sr have been observed below the 4d,/, threshold using two-step laser spectroscopy from the ground State atom 5s' in an atomic beam. Resonant excitations of the autoionizing states are observed by time-of-flight (TOF) analysis of the produced ions. In this experiment via the 4dSp'P, intermediate level, the J = O re~onances are seleaively identified among the other J = I or 2 ones by comparing the line intensities from two spectra recorded with WT and WO polarizations of the two laser beams. From the J = O data. the J = O 4d,/,nd

The even-parity J = 1e, 2e autoionizing spectra of neutral strontium are investigated below the 4d5/2 threshold in a two-step laser experiment via the 4d5p 1P1 level in a strontium atomic beam. The produced Sr+ ions are analysed by a time-of-flight microchannel plate detector. The J final level assignment is obtained by comparing the line intensity dependence from two recorded spectra with pi pi and pi sigma polarizations of the two lasers. More than 400 new resonance lines are measured with an accuracy of +or-0.2 cm-1 for the narrow ones using standard laser calibration procedures. They are assigned to fifteen autoionizing Rydberg series 4dns, 4dn d and 4dng and many perturbers belonging to the 5p6p configuration. Interpretation is made by a combination of the eigenchannel R-matrix and multichannel quantum defect methods (MQDT).

We report what is to our knowledge the first observation of phase-conjugate waves by degenerate four-wave mixing in Ba vapor near its 6s(2)(1)S(0) ? 6s6p(1)P(1) resonance transition. A maximum reflectivity of 36% at 10 mbars of Ar buffer gas pressure is observed together with a temporal pulse shortening of 50%. Conical emission in the two pump waves after their passage through the nonlinear medium is also observed. The dependence of the phase-conjugate signal on the pressure of the Ar buffer gas shows a small state-changing collisional decay rate.