Autocorrelation measurement was demonstrated for the first time to our knowledge in the XUV region to measure the width of a high-order harmonic pulse. Two-photon ionization of rare gases was used as a nonlinear process for the autocorrelation measurement. The 27-fs pulse width that was obtained is, to our knowledge, the shortest in the XUV region.

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Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.

We have demonstrated the second harmonic of a frequency-tripled $\mathrm{Nd}:{\mathrm{YVO}}_4$ laser with 2.5-mW quasi-cw output by using an optically contacted, prism-coupled ${\mathrm{KBe}}_2{\mathrm{BO}}_3{\mathrm{F}}_2$ crystal. We also achieved the second harmonic with a frequency-doubled single-mode Ti:sapphire laser at 172.5 nm and sum-frequency mixing with a dual-wavelength Ti:sapphire laser at 163.3 nm. These wavelengths are to our knowledge the shortest obtained by use of nonlinear crystals for second-harmonic generation and sum-frequency mixing, respectively.