Extension of harmonic cut-off in a waveform controlled laser field by prolonging the recombining period

Abstract

We present a novel waveform synthesized by a half-cycle fundamental wave (800 nm) and a half-cycle subharmonic wave (2400 nm) with an appropriate carrier-envelope phase and a phase delay, in which more ionized electrons can recombine with its parent ions to emit high-order harmonic, giving rise to both the extension of the extreme ultraviolet supercontinuum and the enhancement of harmonic conversion efficiency. An isolated attosecond pulse with considerable energy is obtained as well. By performing time-frequency analyses, it is revealed that the prolonged opposite electric field increases the recombining probability of high-energy electrons.

Isolated short attosecond pulse generation in an orthogonally polarized multicycle chirped laser field

“…Without quantum control of polarized gating the modulation structures exist in the harmonic spectrum due to the interference between short and long trajectories, which would bring about an attosecond pulse with double intensity peaks. Since the pondermotive energy acquired by the electron is inversely proportional to the instantaneous frequency [U p ∝ F /ω 2 (t)], and as we have reported [24], a longer reversed electric field can drive back more higher-energy electrons to recombine with the parent ion by emitting a high-order harmonic, the harmonic cutoff energy will be higher for the smaller ω(t). When it comes to the orthogonal two-color pulse case, owing to the frequency of a 1600-nm pulse being higher than that of the central half cycle of a chirped 800-nm pulse, the harmonic cutoff 033823-3 energy, originating from the central half cycle, is lower than that for the orthogonal chirped pulse.…”