Analytical expression for femtosecond-pulsed Z scans on instantaneous nonlinearity.

By employing the Gaussian decomposition method, the analytical formulas of the Gaussian-beam Z-scan traces have been derived for an optically thin material exhibiting both refractive and absorptive parts of third-order nonlinearity, with Gaussian or hyperbolic secant squared laser pulses of femtosecond duration. The formulas have been verified experimentally with femtosecond-pulsed Z scans on a carbon disulfide and acetone solution of a chalcone derivative (0.95C(18)H(17)ClO(4) . 0.05C(17)H(14)Cl(2)O(3)). An efficient yet accurate analytical technique has been demonstrated for extracting both the nonlinear refraction coefficient and the nonlinear absorption coefficient from a single closed-aperture Z-scan trace.