Optimization of high-order harmonic brightness in the space and time domains
Abstract
Brightness of high-order harmonics is optimized in the space domain by profile flattening and self-guiding of intense femtosecond laser pulse and in the time domain by controlling the laser chirp. The profile flattening and self-guiding of the laser pulse propagating through a long gas jet effectively increased the phase-matched harmonic generation volume, thereby obtaining strong harmonics with low beam divergence, and the laser chirp control allowed the generation of spectrally sharp harmonics. At optimized conditions, the $61\text{st}$ harmonic, obtained at $134\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ from Ne, had a brightness of about $1\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\text{cm}}^{2}∕\text{srad}$ with a beam divergence of 0.5 mrad and a spectral bandwidth of $0.7\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$.