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, u sing femtosecond dynamics of field ionization. We measured the pulse w idth 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 ch ange of transmission of the ninth harmonic for the delay between the p ump and the probe pulses gives both the pulse width of the ninth harmo nic and the recombination time of Kr+. The measured pulse width of the ninth harmonic was 260 fs. The recombination time of Kr+ was similar to 2 ps, which does not contradict the estimated time of the three-bod y recombination. (C) 1996 Optical Society of America