一千五百電子伏特相位匹配高階諧波產生研究

A new phase-matching scheme of ion-based high-harmonic generation (HHG) is proposed. The method can be applied to a wide spectral range, from water window soft x-ray up to 1.5-keV hard x-ray. By using an intense 800-nm pulse focused into a rare-gas-filled capillary waveguide, the phase-matching condition is achieved by balancing the plasma dispersion with the HHG intrinsic dipolephase variation, where the latter is intensity dependent and can be controlled by the driving pulse guiding loss determined by the capillary radius. Furthermore, the time-dependent phase-matching condition automatically gates the harmonic output to an isolated attosecond pulse. The expected pulse duration is as short as about 50 attoseconds. Compared to our previous scheme of quasi-phasematching, which selectively enhances narrow-band harmonic generation to get a high spectral brightness output, the new scheme can be a complementary x-ray source for time-domain applications.