Absolute photoionization cross sections of excited He states in the near-threshold region

The absolute photoionization cross sections of the excited, short-lived He* 1s2p P-1 and 1s3p P-1 states are determined experimentally in the region c lose to the He+ Is S-2 threshold (from 0 to 2 eV). The intermediate He* sta tes are prepared by photoabsorption of a high-order harmonic of an intense picosecond tunable laser and subsequently ionized by absorption of photons of several fixed frequencies, ranging from the near infrared to the ultravi olet. Our experimental results quantitatively confirm earlier theoretical w ork. [S0031-9007(99)09309-6].