Isolated-attosecond-pulse high-order harmonic generation of keV x rays

Using rare-gas ions as the interacting medium, phase-matched high-order harmonic generation up to 1-keV hard x ray can be achieved by balancing the negative plasma dispersion and Gouy phase shift with the positive, intensity-dependent, intrinsic dipole phase variation. The time-dependent phase-matching condition automatically gates the harmonic output to an isolated attosecond pulse. The estimated pulse duration is as short as 120 as.