Autocorrelation measurement was demonstrated for the first time to our
knowledge in the XUV region to measure the width of a high-order harm
onic pulse. Two-photon ionization of rare gases was used as a non-line
ar process for the autocorrelation measurement. The 27-fs pulse width
that was obtained is, to our knowledge, the shortest in the XUV region
. (C) 1998 Optical Society of America.