Second-order nonlinear optical susceptibilities determined through gas-phase experiments

Summary form only given. One of the great challenges in nonlinear optics is the establishment of reliable absolute values of optical nonlinearities as most measurements are made in comparison to a standard material. For third-order nonlinearities this is often fused silica, whereas /spl alpha/-quartz is typically used in second-order nonlinear optics such as e.g. frequency-doubling. Up to now there still exists a considerable uncertainty of the choice of reliable reference materials and standard values. We report on a new procedure based on third-harmonic generation (THG) which yields absolute values for the electronic second- as well as third-order susceptibility. We first calibrate the nonlinear susceptibility of fused silica against the established, quantum chemically calculated second-order hyperpolarizabilities of various gases at different pressures and determine reliable absolute values for fused silica. In a second step we use cascaded frequency-doubling and sum-frequency generation in THG of noncentrosymmetric crystals in combination with THG measurements of fused silica to determine the second-order susceptibility of these crystals.