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Two-color pump-probe experiments in helium using high-order harmonics

Publiceringsår: 2003
Språk: Engelska
Sidor: 3-11
Publikation/Tidskrift/Serie: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics1998-01-01+01:00
Volym: 22
Nummer: 1
Dokumenttyp: Artikel i tidskrift
Förlag: EDP Sciences


A pump-probe technique has been applied for measuring the lifetimes and absolute photoionization cross-sections of excited He states. The 1s2p P-1 and 1s3p P-1 states of He are excited by using the 13th and the 14th harmonic, respectively, of a tunable 70 ps dye laser generated in a Kr gas jet. The states are ionized after a varying time delay, by absorption of probe photons with energies between 1.6 and 4.5 eV. Lifetimes of tau(1s2p) = 0.57 ns and tau(1s3p) = 1.76 ns are determined with a precision of about 15%. A significant enhancement of the number of ions present in the lifetime curves at zero time delay for pressures above 6 x 10(-5) mbar is attributed to direct two-photon ionization of He in combination with AC Stark broadening of the excited state and absorption of the XUV light in the medium. Absolute photoionization cross-sections from the He 1s2p P-1 and He 1s3p P-1 states in the threshold region are determined by measuring the saturation of the ionization process with a precision of similar to 25%. In addition, the variation of the relative orientation between the polarization vectors of the pump and probe beams enables the determination of partial photoionization cross-sections.


  • Atom and Molecular Physics and Optics


  • ISSN: 1434-6060

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