Femtosecond measurement of high-order harmonic pulse width and electron recombination time by field ionization

We measured the ultrashort XUV pulse width by the pump-probe method, using femtosecond dynamics of field ionization. We measured the pulse width of the ninth harmonic (88.3 nm) of a Ti:sapphire laser, using the difference of the absorption cross section between Kr and Kr(+). The change of transmission of the ninth harmonic for the delay between the pump and the probe pulses gives both the pulse width of the ninth harmonic and the recombination time of Kr(+). The measured pulse width of the ninth harmonic was 260 fs. The recombination time of Kr(+) was ~2 ps, which does not contradict the estimated time of the threebody recombination.