We investigate the role of core potential in high ionization potential systems on high harmonic generation (HHG) spectra and obtain attosecond pulses. In our scheme, we use a standard soft core potential to model high ionization potential systems and irradiated these systems with fixed laser parameters. We observe the role of these systems on all the three steps involved in HHG process including ionization, propagation and recombination. In our study, the results illustrate that for high ionization potential systems, the HHG process is more sensitive to the ionization probability compared to the recombination amplitude. We also observe that due to the stronger core potential, small oscillations of the electrons during the propagation do not contribute to the HHG spectrum, which implies the dominance of only long quantum paths in the HHG spectrum. Our results, for attosecond pulse generation, show that long quantum path electrons are responsible for the supercontinuum region near the cutoff, which is suitable for the extraction of a single attosecond pulse in this region.
M R Sami and A Shahbaz† Role of quantum paths in generation of attosecond pulses 2020 Chin. Phys. B 29 104207
Fig. 1.
(a) Potential as a function of the distance from the nucleus and (b) the corresponding potential depths as a function of Ip.
Fig. 2.
Calculated HHG spectra through numerical simulation of 1D-TDSE, considering potentials given in Fig. 1.
Fig. 3.
(a) Recombination amplitudes for all potentials given in Fig. 1. (b) Calculated ionization probabilities corresponding to each system given in Fig. 1, when these are irradiated by an external electric field of fixed laser parameters.
Fig. 4.
Electron wavefunction density for systems having (a) Ip = 2.0 a.u. and (b) Ip = 2.5 a.u.
Fig. 5.
Time-frequency distribution of the HHG spectra when model potentials given in Fig. 1 are exposed to a single 5 fs/800 nm laser field with a peak intensity of 1.0 × 1015 W/cm2. Long and short quantum trajectories are calculated only for 1.5 cycles for a cosine-like pulse. These laser parameters are kept to be constant for each system, where (a) Ip = 2.0 a.u., (b) Ip = 2.1 a.u., (c) Ip = 2.2 a.u., (d) Ip = 2.3 a.u., (e) Ip = 2.4 a.u., (f) Ip = 2.5 a.u.
Fig. 6.
(a) The temporal profile of the attosecond pulses by superposing harmonics from the 130th to 165th order for the system with Ip = 2.0 a.u. and (b) the temporal profile of the attosecond pulses by superposing harmonics from the 140th to 175th order for the system with Ip = 2.5 a.u.
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