Measurement of Multiple Components of the Molecular Frame Third-order Nonlinear Response Tensor in Impulsively Aligned CO2 Molecules

We perform measurements of multiple components of the molecular frame third-order nonlinear response tensor (second hyper-polarizability) in impulsively aligned carbon dioxide (CO2) molecules. We use a moderately strong femtosecond near-infrared laser pulse to impulsively align CO2 molecules, and use a pair of femtosecond pulses to measure the non-linear response using the Optical Kerr effect. The non-linear response is measured at a rotational revival for different alignment pulse polarization angles which allows us to measure multiple molecular frame tensor components. We then extend this to a snapshot measurement where we use an azimuthally polarized vector beam for alignment and a focal volume imaging scheme to measure nonlinear response for different alignment angles simultaneously. We interpret the tensor components in terms of symmetries of the valence electronic character. These studies are an important step towards using non-linear response tensor measurements to study ultrafast dynamics on electronically excited states in molecules.