Phase-matched high-order harmonic generation in a gas cell with midinfrared femtosecond pulses

Abstract

We experimentally investigate the generation of high-order harmonics in a $4\text{\ensuremath{-}}\mathrm{mm}$-long gas cell using midinfrared femtosecond pulses at various wavelengths of $1240\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, $1500\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, and $1800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. It is observed that the yield and cutoff energy of the generated high-order harmonics critically depend on focal position, gas pressure, and size of the input beam which can be controlled by an aperture placed in front of the focal lens. By optimizing the experimental parameters, we achieve a cutoff energy at $\ensuremath{\sim}190\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ with the $1500\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ driving pulses, which is the highest for the three wavelengths chosen in our experiment.