Extending the High-Order Harmonics Plateau and Isolated Attosecond Pulse Generation in an Intense Three-Color Laser Field

Abstract

We propose a method to extend the high-order harmonics plateau and generate an isolated sub-10-as pulse by adding a weak control pulse (10 fs, 1600 nm) to modify a two-color laser field (5 fs, 800 nm; 10 fs, 400 nm). The numerical results show that the plateau is extended obviously in the three-color laser field regime. Additionally, the ionization rate and classical returning kinetic-energy maps are calculated to better understand the physical origin of the high-order harmonics generation (HHG). By means of the ionization probability and the time-frequency distributions, more features of the HHG are revealed. Furthermore, our simulations show that the width of the plateau and the relative conversion efficiency of the harmonic spectra are highly dependent on the relative phase. Finally, by adjusting the relative phase and superposing a properly selected range of the HHG spectrum, an isolated attosecond pulse with a duration of 7 as is obtained.

Generation of isolated attosecond pulses by polarization gating of high-order harmonic emission from $\boldsymbol {\rm H_2^+}$ in intense ultrashort laser fields

“…The mechanism of HHG process can be interpreted by a three-step semiclassical model [4][5][6]: first, under an intense laser field, the bound state electron tunnels through the coulomb barrier into continuum, then the freed electron accelerates in the external laser field and finally it may recombine into the ground state due to the phase change of the electric field followed by attosecond burst of electromagnetic waves emission. In many cycle laser fields this process occurs every halfcycle and generates attosecond pulse trains which due to the interference of these attosecond pulses there is a frequency comb with an interval of twice the driving field photon energy.…”

Broadband-Isolated Attosecond Pulse Generation by Two-Color Elliptically Polarized Laser Pulses

“…[12][13][14][15][16][17] The emission of HHG can also be extended by three-color scheme. [18,19] Besides, HHG spectrum can be enhanced by orthogonally polarized two-color field or two-color polarized gating plasmonic field. [20,21] Polarization gating (PG) scheme has been proved to be a powerful method to generate IAP, where a left and a right circularly polarized laser pulse with the same frequency were combined together.…”

Generation of an extreme ultraviolet supercontinuum in a two-color spatially inhomogeneous field

“…Recently, Zhao et al [8] have produced a 67 as pulse with a 7 fs/750 nm laser pulse, which is the known shortest attosecond pulse at present. Furthermore, ionization gating [9], acceleration gating [10], chirped pulse [11], double optical gating [12,13], multi-cycle laser sources [14], and two-color or multi-color control scheme [15][16][17][18][19][20][21][22][23][24] have been proposed for generating desirable isolated attosecond pulses. An alternative method for generating a broadband attosecond pulse is controlling quantum paths, which can significantly modulate the HHG process.…”