Fig. 1. Harmonic spectra of He⁺ driven by different laser fields. (a) Chirped and spatially inhomogeneous fields; (b) spatially inhomogeneous chirped field

Fig. 2. Harmonic spectra and emitted efficiency of the supercontinuum. (a) Harmonic spectra in the spatially inhomogeneous chirped field with different p values; (b) emitted efficiency of the supercontinuum from 240th to 1210th order as a function of p

Fig. 3. Time-frequency distributions for the HHG spectra. (a) Single chirped field; (b) single spatially inhomogeneous field; (c) spatially inhomogeneous chirped field

Fig. 4. Temporal profiles of the attosecond pulses by superposing different order harmonics. (a) Chirped and spatially inhomogeneous fields; (b)-(d) spatially inhomogeneous chirped field

Fig. 5. Classical trajectory simulation and electric fields of the laser pulses. (a)-(c) Dependence of the harmonic order on the ionization and emission times in three light fields; (d) electric field of the laser pulse with central wavelength of 800 nm and pulse width of 5 fs; (e) electric field of the chriped laser pulse with central wavelength of 800 nm and pulse width of 5 fs

Fig. 6. HHG spectrum and time-frequency distribution in the spatially inhomogeneous chirped field with t₀=105 a.u.. (a) HHG spectrum; (b) time-frequency distribution

Fig. 7. Temporal profile of the attosecond pulse by superposing the harmonics from 1090th to 1450th order in the spatially inhomogeneous chirped field with t₀=105 a.u.