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Dissociating diatomic molecules in ultrafast and intense light
摘要： An ab initio theory is devised for the quantum dynamics of molecules undergoing multiple ionization in ultrafast and intense light. Specifically, the intertwined problem of photoionization, radiative, and electronic transitions in the course of dissociation is addressed which arises, e.g., when molecules are exposed to xuv light or x rays from free electron lasers or attosecond light sources, but the approach is equally useful in optical strong-field physics. The coherent interaction of the molecule with the light in a specific charge state is also treated. I set out from an abstract formulation in terms of the quantum optical notion of system-reservoir interaction using a master equation in Lindblad form and analyze its short-time approximation. First, I express it in a direct sum rigged Hilbert space for an efficient solution with numerical methods for systems of partial differential equations. Second, I derive a treatment via quantum Monte Carlo wave packet (MCWP) propagation. The formalism is concretized to diatomic molecules in Born-Oppenheimer approximation whereby molecular rotation is disregarded. The numerical integration of the master equation is carried out with a suitably factored density matrix that exploits the locality of the Hamiltonian and the Lindblad superoperator with respect to the internuclear distance. The formulation of the MCWP for molecules requires a thorough analysis of the quantum jump process; namely, the dependence on the continuous distance renders a straight wave packet promotion useless and, instead, a projected outer product needs to be employed involving an integrated quantum jump operator.
关键词： Ultrafast and intense light,Born-Oppenheimer approximation,Dissociation of diatomic molecules,Quantum Monte Carlo algorithm,Master equation in Lindblad form
更新于2025-09-10 09:29:36
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Direct excitation of molecular vibrational motion by intense broadband THz pulses
摘要： We theoretically investigate molecular vibrational dynamics driven by intense and broadband THz pulses. The light-nuclei interaction is derived from a fully quantum-mechanical minimal coupling Hamiltonian to analyse direct excitation of vibrational modes by the THz pulses. We show that for diatomic molecules a "vibrational moment" can be defined in a manner similar to the dipole moment and that it has non-zero values only for heteronuclear diatomic molecules. Taking ultra-cold heteronuclear diatomic molecules as examples, we show that vibrational-mode excitation by THz pulse irradiation occurs almost stepwisely, especially for low vibrational modes. Coherent control method using frequency-controlled THz pulse sequence is also proposed.
关键词： quantum-mechanical minimal coupling Hamiltonian,vibrational moment,heteronuclear diatomic molecules,coherent control,molecular vibrational dynamics,THz pulses
更新于2025-09-09 09:28:46
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Influence of the alignment angle of molecules on the cutoff of the high-order harmonics
摘要： Using the Lewenstein model combined with the Ammosov–Delone–Krainov (ADK) ionization theories, the high-order harmonic generation (HHG) of the diatomic molecules O2 and N2 at the various alignment angles are investigated. We find that the cutoff of harmonic spectra from the aligned O2 and N2 are influenced by the alignment angles. The dependence of the cutoff energy on the alignment angle is attributed to the anisotropy in the molecular ionization, which is rooted in the nonuniform electron distributions of the highest occupied molecular orbital. If the polarization of the laser crosses the denser region of the electron cloud, the ionization rate is larger, and then the saturation laser intensity is smaller, therefore the harmonic spectra are cut off at the lower energy.
关键词： Ionization suppression,Alignment dependent harmonic spectra,Diatomic molecules
更新于2025-09-09 09:28:46
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Photon-momentum transfer in diatomic molecules: An <i>ab initio</i> study
摘要： For a molecule, the two-center interference and the molecular scattering phase of the electron are important for almost all the processes that may occur in a laser field. In this study, we investigate their effects in the transfer of linear photon momentum to the ionized electron by absorbing a single photon. The time-dependent Schr?dinger equation of H2+ is numerically solved in the multipolar gauge in which the electric quadrupole term and the magnetic dipole term are explicitly expressed. This allows us to separate the contributions of the two terms in the momentum transfer. For different configurations of the molecular and the laser orientation, the transferred momentum to the electron is evaluated at different internuclear distances with various photon energies and two-center interferences are identified in the whole region. At small electron energies and small internuclear distances, we find significant deviations from the prediction of the classical double-slit model due to the strong mediation of the Coulomb potential. Finally, even for a large internuclear distance, our results show that a varying molecular scattering phase is important at all electron energies, which is beyond the simple prediction of the linear combination of the atomical orbitals.
关键词： diatomic molecules,molecular scattering phase,ab initio study,photon-momentum transfer,two-center interference
更新于2025-09-04 15:30:14