Z -scan: a Simple and Sensitive Technique for Nonlinear Refraction Measurements

We describe a sensitive technique for measuring nonlinear refraction in a variety of materials that offers simplicity, sensitivity and speed. The transmittance of a sample is measured through a finite aperture in the far -field as the sample is moved along the propagation path (z) of a focused Gaussian beam. The sign and magnitude of the nonlinearity is easily deduced from such a transmittance curve (Zscan). Employing this technique a sensitivity of better than A /300 wavefront distortion is achieved in n2 measurements of BaF2 using picosecond frequency doubled Nd:YAG laser pulses.