Generation of intense isolated sub-40-as pulses from a coherent superposition state by quantum path control in the multicycle regime

Abstract

We theoretically investigate high-order harmonic generation and attosecond pulses by numerically solving the three-dimensional time-dependent Schrödinger equation from a helium ion in a two-color laser field, which is synthesized by adding a 1600-nm laser pulse to a multicycle 800-nm laser pulse. The numerical results show that the short quantum path selection and broadband continuum spectra are achieved by adjusting the relative phase between two laser pulses, and isolated attosecond pulses can be generated successfully. Compared with the case of He + ions from the 1s ground state, the emission efficiency of the continuous harmonics and the intensity of the isolated attosecond pulse are enhanced approximately thirteen orders of magnitude by preparing He + ions in a coherent superposition of the states 1s and 2s. Furthermore, the bandwidth of the continuum spectrum is further broadened by increasing the intensity of the 1600-nm laser pulse, and an intense 38-as isolated pulse with a bandwidth of 109 eV is straightforwardly obtained.

High-order harmonic generation spectra and isolated attosecond pulse generation with a two-color time delayed pulse

“…Fig. 3(c) and (f) shows the corresponding dependence of the kinetic energies on the ionization and recombination times calculated by [12,13,29],…”

“…where t 1 and t 2 are the ionization and the recombination times of the electron, and the maximum kinetic energy E k of an electron ionized at t 1 and returning to the parent ion at t 2 can simply be expressed as [29],…”

“…Within this framework, Zeng et al [28] theoretically obtain an isolated 65as pulse through the combination of an 800 nm fundamental field and a 400 nm controlling field. Chen et al [29] theoretically obtained an isolated 38as pulse by using an 800 nm fundamental field combined with a 1600 nm controlling field. Lu et al [30] theoretically obtain an ultrashort 21as pulse by using a synthesized three-color field (800 nm, 400 nm and 1600 nm).…”

Quantum path control on the harmonic emission in the presence of a terahertz field

“…However, for the practical application, an isolated attosecond pulse obtained from the continuum HHG spectrum is more useful to trace the ultrafast electronic dynamics process. In order to produce an isolated attosecond pulse from a continuum harmonic spectrum, many methods aiming to control the movement of the emitted electron have been proposed, such as the few-cycle driving pulse scheme [12,13], the polarization gate scheme [14,15], the chirp pulse scheme [16,17], and the two-color or multi-color pulses scheme [18][19][20] etc. The shortest pulse duration achieved by these methods are about 80 as [12] and sub-10 as [20] from the experimental and the theoretical sides, respectively.…”

Single quantum path control by a fundamental chirped pulse combined with a subharmonic control pulse

“…However, when a single quantum path is well selected, a regular isolated attosecond pulse can be produced [31]. Concerning the single quantum path control for high-order harmonics, Chen et al [32] theoretically investigate its relationship to the carrier-envelope phase (CEP) effect between the intense 800 nm fundamental field and the 1600 nm control pulse and obtain an isolated 38 as pulse. Wu et al [33] theoretically investigate the role in the control of the chirp parameter effect of a few-cycle 1200 nm chirped pulse and obtained an isolated 65 as pulse.…”