Optimal improvement of harmonic spectra driven by the fixed intensity chirped combined pulses

A potential scheme to obtain the optimal improvement of high harmonic spectra has been proposed by using the fixed intensity chirped combined pulse. It shows that with the introduction of two-color, three-color and four-color chirps, not only the harmonic cutoff energy can be extended to 20.0Up, but also the harmonic intensity is enhanced compared with those from the single-color chirp-free and chirped pulses with the same laser intensity. As a result, the broader and stronger harmonic plateau, contributed by a single quantum harmonic path can be obtained, which can support the production of the attosecond pulse shorter than 32 as.