Measurement of molecular polarizability anisotropy via alignment-induced spatial focusing and defocusing

We demonstrate that the polarizability anisotropy of the acetylene molecule could be experimentally determined by molecular alignment-induced spatial focusing and defocusing effects under femtosecond impulsive excitation. The molecular alignment signals of oxygen and acetylene were measured under identical experimental conditions and the polarizability anisotropy of acetylene was quantitatively determined with oxygen as the reference molecule. Meanwhile, the Kerr coefficients of oxygen and acetylene were estimated. This intuitive and simple method is also applicable to other molecules.