LIMAO: Cross-platform software for simulating laser-induced alignment and orientation dynamics of linear-, symmetric- and asymmetric tops

Abstract

A user-friendly and cross-platform software called Laser-Induced Molecular Alignment and Orientation simulator (LIMAO) has been developed. The program can be used to simulate within the rigid rotor approximation the rotational dynamics of gas phase molecules induced by linearly polarized intense laser fields at a given temperature. The software is implemented in the Java and Mathematica programming languages. The primary aim of LIMAO is to aid experimental scientists in predicting and analyzing experimental data representing laser-induced spatial alignment and orientation of molecules. Program summaryProgram title: LIMAOProgram Files doi: http://dx.doi.org/10.17632/x7h287gc9p.1Licensing provisions: GNU General Public License 3 (GPL)Programming languages: JAVA, MathematicaSupplementary material: LIMAO_SM.pdfNature of problem: LIMAO is a user-friendly software, which can be used to compute the temporal evolution of the laser-induced alignment and orientation [1-3] of gas phase molecules at a given temperature within the rigid rotor approximation. The user is asked to provide (i) molecular parameters such as rotational constant(s), a dipole moment, polarizabilities, and nuclear spin-statistical weights for the rotational levels, (ii) external field parameters such as time when the laser pulse becomes maximum, the pulse width, the intensity and carrier frequency of laser pulse(s), and (iii) temperature as input data. As an output, LIMAO generates the temporal evolution of the expectation values of physical quantities of molecules representing the spatial alignment and orientation.Solution method: LIMAO solves numerically the time-dependent Schrödinger equation of a rigid rotor molecule interacting with a time-dependent external field. The time-dependent rotational wave packet is expanded by the field-free stationary rotational eigenstates of the system. The solution is obtained by the following four steps: (i) the rotational eigenstates are derived and their symmetries within the corresponding molecular rotation group are assigned, (ii) the matrix representation of the time-dependent Hamiltonian, containing the interaction terms with an external light field as well as the matrix representations of physical quantities to be observed are constructed using the rotational eigenstates, (iii) the initial populations in the respective rotational eigenstates are determined by the Boltzmann distribution at a given temperature, and (iv) the wave packets are propagated in time and the expectation values of the relevant physical quantities are computed as a function of time.Additional comments including Restrictions and Unusual features: Simulations with the LIMAO software are limited to the rotational degrees of freedom. Light-induced vibrational excitations are neglected and light-induced electronic excitations are only accounted for in a perturbative manner through molecular polarizabilities. Therefore, the results obtained by LIMAO simulations should be treated with caution when dynamical processes such as light-induced deformation of geometrical structure, resonant vibrational excitation, and electronic excitation beyond the perturbative regime need to be considered.