Damping wave packet approach: a calculation method of nonperturbative nonlinear optical susceptibilities including effects of nuclear motion at finite temperatures

A method is developed for a nonperturbative calculation of nonlinear optical susceptibilities for specific systems such as low-density gases or single molecule systems, including effects of nuclear motion. Nuclear motion is treated quantum-mechanically by wave packet dynamics with population damping effects. As an example, the effects of temperature and mass on the third-order susceptibilities for a three-atom cation model system are examined.