Half-cycle cutoff in near-threshold harmonic generation

Abstract

A half-cycle cutoff is identified in the harmonic generation spectra near the ionization potential for short driving laser pulses. Unlike the half-cycle cutoff in the high-energy region, the newly found lowenergy cutoff is strongly affected by the ionic potential and multiple return trajectories. We show their contribution clearly in the observable harmonic spectrum based on the reference of this cutoff structure. Our results are calculated from a numerical solution to the 3D time-dependent Schrödinger equation and a classical trajectory Monte Carlo method. By comparing the results from both methods, we analyze the time-dependent sub-cycle electron dynamics and provide a transparent explanation to this half-cycle cutoff. We further investigate the low-energy harmonic yield as a function of CEP for different pulse durations. The modulation depth of this yield drops rapidly when the pulse duration is increased, which can explain the CEP-dependence recently observed in the experiment.

Disentangling Long Trajectory Contributions in Two-Colour High Harmonic Generation

“…These findings agree with Ref. [42], where Xiong et al also conclude that a recombination distance equal to the exit point was necessary to yield the correct description for short trajectories in the near-threshold part of the HHG spectrum. When checking the kinetic energy at a closer specific radius, then short trajectories gain additional kinetic energy from being accelerated by the laser field while travelling closer to the ion (see Figures 3B and 4).…”

Controlling quantum numbers and light emission of Rydberg states via the laser pulse duration

“…2(g). The return condition for each trajectory was a shorter distance to the ion than the individual exit radius, which is known to reproduce TDSE and experimental results [69,74]. The CTMC trajectories are grouped according to the ionization events occurring during one of the three lobes of the driving field, indicated by different colors in Fig.…”

Controlling polarization of attosecond pulses with plasmonic-enhanced bichromatic counter-rotating circularly polarized fields

“…2(g). The return condition for each trajectory was a shorter distance to the ion than the individual exit radius, which is known to reproduce TDSE and experimental results [69,74]. The CTMC trajectories are grouped according to the ionisation events occurring during one of the three lobes of the driving field, indicated by different colors in Fig.…”