Waveform control in high-order harmonic generation via chirp gating technology

Laser waveform control in high-order harmonic generation (HHG) has been investigated and discussed by using the two-color chirp gating technology. It is found that the multiple-acceleration-recombination process in HHG can be found in a specific 'W' waveform structure. Moreover, by changing the chirp forms as well as laser parameters, the multiple-acceleration-recombination process in the 'W' waveform structure can be controlled, which leads to the remarkable improvements of harmonic cutoff and harmonic yield. Consequently, a water window spectral continuum with a bandwidth of 488 eV and with an intensity enhancement of 10 times can be obtained. Further, by the Fourier transformation of some selected harmonics on this spectral continuum, three single attosecond pulses (SAPs) with the pulse durations of 38 as can be produced. With the introduction of inhomogeneous effect of the laser field, the HHG spectra with a larger harmonic cutoff and a broader spectral continuum can be obtained. Consequently, by the Fourier transformation of some selected harmonics on the spectral continuum, a number of water window SAPs with the pulse durations of 36 as can be obtained.