High-order harmonic pulse characterization by using femtosecond ionization dynamics of singly charged ions of rare gas

This study describes a technique for measuring high-order harmonic duration based on the cross-correlation between a high-order harmonic pulse and the ionization dynamics of rare gas induced by an intense laser field, namely optical-field-induced ionization (OFI). This technique makes use of the rapid population change of rare gas atoms induced by OFI as an ultrafast absorption shutter for the harmonic pulse. Although the idea of using OFI for temporal characterization was demonstrated in pioneering studies, the idea is developed by replacing neutral atoms with singly charged ions. An improved technique is used to measure the pulse duration of high-order harmonics in the soft X-ray region with a resolution of a few tens of femtoseconds.