GENERALIZED MULTIPHOTON-IONIZATION CROSS-SECTIONS OF THE RARE-GASES FOR 500-FS, 248.6-NM PULSES

Absolute values for the generalized multiphoton-ionization cross secti ons and saturation intensities of rare gases are reported for 500-fs, 248.6-nm pulses. For He, Ar, and Kr these values are experimentally de termined from the intensity dependence of the ponderomotive shift for intensities comparable to and above the saturation intensity. The meas ured experimental cross sections [sigma((5))(He) = (0.9(+9)(-0.4)) X 1 0(-152) cm(10)s(4), sigma((4))(Ar) = (1.3(+1)(-0.5)) X 10(-116) cm(8) s(3), sigma((3))(Kr) = (1.2(+1.7)(-0.6)) X 10(-82) cm(6) s(2), sigma(( 3))(Xe) = (50(-45)(+350)) X 10(-82) cm(6) s(2)] are found to be in goo d agreement with theoretical values [sigma((5))(He) = 4.4 X 10(-152) c m(10) s(4) (ab initio), sigma((4))(Ar) = 1.1 X 10(-115) cm(8) s(3) (sc aling), sigma((3))(Kr) = 0.7 X 10(-82) cm(6) s(2) (scaling), sigma((3) )(Xe) = 5 X 10(-82) cm(6) s(2) multichannel quantum defect theory]. Fo r Ne it is found that a single-rate description is not valid, and ther efore the present model for the analysis of the experimental results c annot be applied. The reported Xe experimental cross sections are base d on the conventional method of measuring the ion yield vs laser inten sity with its concomitant reduced accuracy. [S1050-2947(98)00201-7].