Electron‐Nuclear Dynamics in Molecular Harmonic Generation Driven by a Plasmonic Nonhomogeneous Field

Abstract

Electron (z)-nuclear (R) dynamics in the molecular high-order harmonic generation (MHHG) from H 2 + driven by the plasmonic nonhomogeneous field, generated by the surface plasmon polaritons in the bowtie-shaped nanostructure, have been theoretically investigated through solving the two dimensional time-dependent Schrödinger equation with the Non-Bohn-Oppenheimer approximation. It is found that (i) due to the plasmonic enhancement of the laser intensity, the harmonic cutoff can be extended when the spatial position of H 2 + is away from the gap center of the nanostructure. However, due to the limit of the gap size, the threshold value of the harmonic cutoff can be obtained at a given position of H 2 + . (ii) Due to the asymmetric enhancement of the laser intensity in space, the extended higher harmonics are respectively from E(t) > 0 a.u. or E(t) < 0 a.u. for the cases of the positive and the negative spatial position of H 2 + . As a result, the intensities of the extended higher harmonics are different and can be controlled by changing the carrier-envelope phase and the pulse duration of the laser field. (iii) In the few-cycle pulse duration, the MHHG mainly comes from the multi-photon resonance ionization (MPRI), while as the pulse duration increases, the MPRI, the charge-resonance enhanced ionization (CREI) and even the dissociative ionization (DI) are contributed to the MHHG. Moreover, as the spatial position of H 2 + moves, the contributions of the MHHG from the MPRI, the CERI and the DI can be controlled. (iv) The contributions of the MHHG from the two-H nuclei have been investigated and found that when E(t) > 0 a.u., the intensities of the harmonics from the negative-H is higher than those from the positive-H; while when E(t) < 0 a.u., the intensities of the harmonics from the positive-H plays the main role in the MHHG. Moreover, the multi-minima, caused by the two-center interference can also be found. (v) Finally, by superposing a properly selected harmonics, a single isolated attosecond pulse (SIAP) with the full width at half maximum (FWHM) of 34 as can be obtained.

Role of nuclear dynamics in high harmonic generation redshift of H2 +

“…Furthermore, redshift in HHG is commonly expected for any molecule beyond the Born-Oppenheimer approximation [17,18]. In recent years, great effort has been made to probe the effect of nuclear dynamics on high harmonic spectroscopy [19][20][21].…”

Rydberg electron focused by Coulomb potential to enhance high-order harmonic generation via the chirped laser

“…For both spectroscopic applications and the optimization of attosecond pulses, it is necessary to increase the cut-off frequency and the conversion efficiency of the HHG. A lot of methods have been performed to achieve it, such as the twocolor laser field and the nano-plasmonic enhancement field [20][21][22][23][24][25]. Since the ponderomotive energy is proportional to the square of the wavelength of the driving field (U p ∝λ 2 ) according to the three-step model, the long-wavelength laser field, such as mid-infrared laser field, was extensively introduced to be the driving field in order to improve the cut-off frequency of the HHG [26][27][28][29][30][31].…”