Shaped Post-Field Electronic Oscillations in H2+ Excited by Two-Cycle Laser Pulses: Three-Dimensional Non-Born–Oppenheimer Simulations

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• 作者：Guennaddi K. Paramonov ; O. Kühn ; André D. Bandrauk
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：May 19, 2016
• 年：2016
• 卷：120
• 期：19
• 页码：3175-3185
• 全文大小：619K
• 年卷期：0
• ISSN：1520-5215

文摘

Quantum dynamics of H₂⁺ excited by two-cycle laser pulses with laser carrier frequencies corresponding to the wavelengths λ_l = 800 and 200 nm (corresponding to the periods τ_l = 2.667 and 0.667 fs, respectively) and being linearly polarized along the molecular axis have been studied by the numerical solution of the non-Born–Oppenheimer time-dependent Schrödinger equation within a three-dimensional (3D) model, including the internuclear distance R and electron coordinates z and ρ. The amplitudes of the pulses have been chosen such that the energies of H₂⁺ after the ends of the laser pulses, ⟨E⟩ ≈ −0.515 au, were close to the dissociation threshold of H₂⁺. It is found that there exists a certain characteristic oscillation frequency ω_osc = 0.2278 au (corresponding to the period τ_osc = 0.667 fs and the wavelength λ_osc = 200 nm) that plays the role of a “carrier” frequency of temporally shaped oscillations of the expectation values ⟨−∂V/∂z⟩ emerging after the ends of the laser pulses, both at λ_l = 800 nm and at λ_l = 200 nm. Moreover, at λ_l = 200 nm, the expectation value ⟨z⟩ also demonstrates temporally shaped oscillations after the end of the laser pulse. In contrast, at λ_l = 800 nm, the characteristic oscillation frequency ω_osc = 0.2278 au appears as the frequency of small-amplitude oscillations of the slowly varying expectation value ⟨z⟩ which makes, after the end of the pulse, an excursion with an amplitude of about 4.5 au along the z axis and returns back to ⟨z⟩ ≈ 0 afterward. It is found that the period of the temporally shaped post-field oscillations of ⟨−∂V/∂z⟩ and ⟨z⟩, estimated as τ_shp ≈ 30 fs, correlates with the nuclear motion. It is also shown that vibrational excitation of H₂⁺ is accompanied by the formation of “hot” and “cold” vibrational ensembles along the R degree of freedom. Power spectra related to the electron motion in H₂⁺ calculated for both the laser-driven z and optically passive ρ degrees of freedom in the acceleration form proved to be very interesting. In particular, both odd and even harmonics can be observed.