Taras Shevchenko Kyiv National University, Department of Physics 4, Glushkov Ave., 03022 Kyiv, Ukraine *Corresponding author e-mail: sgr@univ.kiev.ua

Abstract. Degenerate four-wave mixing (DFWM) processes in carbon disulfide have been experimentally studied applying the wavelength dependent femtosecond laser source. The quantum mechanical perturbation theory was applied to analyze the experimental data. Third-order optical nonlinearity in carbon disulfide has been proposed to consider two- or three-energy levels schemes. Either two-levels or three-levels scheme prevails in the nonlinear interaction depending on the symmetry of the participating in the interaction molecular orbitals. These two DFWM schemes have different spatial symmetry of three wave vectors of the laser beams, which leads to DFWM signal shape variation. Registered DFWM signals demonstrate the presence of a slow decay component for longer light wavelengths, which indicates availability of a virtual level in carbon disulfide having the same symmetry inherent to the ground state with 1.12 picoseconds lifetime. The DFWM signal shape based on symmetries of the carbon disulfide ground state and excited states has been analyzed. Quantum mechanics calculus was performed to build wave functions for the highest occupied (HOMO) and lowest unoccupied molecular orbitals (LUMO). Electronic states energies as well as optical transition energy for carbon disulfide were calculated with a few percents accuracy.

Keywords: third-order optical nonlinearity, carbon disulfide, perturbation theory, virtual levels.

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