2020 Fiscal Year Research-status Report
Efficient simulation of coupled electronic and nuclear motion in molecules in intense laser fields
| Project/Area Number |
18K05024
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| Research Institution | The University of Tokyo |
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Principal Investigator |
LOETSTEDT ERIK 東京大学, 大学院理学系研究科(理学部), 准教授 (80632984)
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| Project Period (FY) |
2018-04-01 – 2022-03-31
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| Keywords | Strong-field science / TDSE / Particle correlation |
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| Outline of Annual Research Achievements |
During the fiscal year 2020, I have accomplished two main results.
(i)Establishment of an accurate formula for strong-field ionization rates of He-like ions (published in Physical Review A). Together with a collaborator (M. F. Ciappina), I calculated the static-field ionization rates of He-like ions using the multiconfiguration time-dependent Hartree-Fock (MCTDHF) method. By fitting the results of the ionization rates obtained using the MCTDHF method to a fitting formula, we derived a convenient expression providing accurate field ionization rates for He-like ions, valid in both the tunneling and the over-the-barrier regimes of ionization. The derived formula will be useful in implementing a recently proposed scheme for measuring the focal intensity of ultraintense laser pulses.
(ii)Together with T. Nishi and K. Yamanouchi, we found a new type of phase relevant for the photoionization process in molecules (published in Physical Review A, Rapid communication). When an electron is ejected from a molecule by the absorption of a photon, a vibrational wave packet is created in the molecular ion. We found that the phase of the outgoing photoelectron is imprinted on the vibrational wave packet, resulting in an additional phase in the off-diagonal elements of the vibrational density matrix. This phase, equivalent to a time delay of the order of tens of attoseconds, can be measured by a pump-probe scheme where the kinetic energy release of the ionic fragments is recorded.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The present project aims at establishing an efficient method for the simulation of coupled electronic and nuclear motion of molecules expose to an intense laser field. During fiscal year 2020, I have started to derive the equations of motion for a method where the standard Born-Oppenheimer approximation (BOA) is combined with the Extended multiconfiguration time-dependent Hartree-Fock (Ex-MCTDHF) method. The idea is to treat the main part of the wave function corresponding to dissociation and electronic excitation by the BOA, and the remaining (small) part of the wave function corresponding to ionization by the Ex-MCTDHF method. In order to obtain reference results by which the results of the new method can be compared, a computer code which implements a numerically exact method, the BOA, and the Ex-MCTDHF method has been written for a one-dimensional model of the hydrogen molecular ion (H2+). While previous applications of the Ex-MCTDHF method to H2+ failed in describing ionization proceeding simultaneously with dissociation, the hope is that the present method will be able to efficiently describe both dissociation, electronic excitation as well as ionization of a molecule exposed to an intense laser field.
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| Strategy for Future Research Activity |
During the final fiscal year of the present project, I plan to finish the derivation of the combined BO--Ex-MCTDHF method, and to implement the method for the simulation of a one-dimensional model of the hydrogen molecular ion (H2+). The H2+ molecular ion is an ideal model system for testing the ability of the method to describe the simultaneous processes of electronic excitation, ionization, vibrational excitation and ionization. Rotation of the molecule is not included in the one-dimensional model. After the completion of a computer program which implements the method, simulations will be conducted for different laser parameters such as intensity and wavelength. Comparison will be made by results obtained by the following reference methods (i) Numerically exact results without approximations, (ii) The standard BO approximation, (ii) The Ex-MCTDHF method. I aim to show that the present method is more accurate than the both the BO approximation and the Ex-MCTDHF method. When interesting results have been obtained, a summary of the results will be written up for submission to a scientific journal.
I also aim to present the results obtained within the present project at at least one international meeting which has been postponed from 2020 to 2021.
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| Causes of Carryover |
The amount to be used in FY 2021 was planned to be used in FY 2020 for travelling to an international conference which was postponed because of the outbreak of COVID-19. The leftover amount will be used to present the results obtained within the present project at the conference scheduled in 2021.
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