Z-SCAN AND EZ-SCAN MEASUREMENTS OF OPTICAL NONLINEARITIES

Abstract

We describe the application of single beam propagation methods, namely Z-scan and EZ-scan, for the determination of nonlinear refractive indices in materials including thin films. In these experiments the transmittance of a sample is measured either through a finite aperture (Z-scan) or around an eclipsing disk (EZ-scan) placed in the far-field as the sample is moved along the propagation path (Z) of a focused beam. Both methods can also be used to separately measure the nonlinear absorption so that both the real and imaginary parts of the nonlinear susceptibility are determined along with their signs. The sensitivity to induced phase distortion depends on the sensitivity of the measuring apparatus to transmittance changes ΔT. For the 10 Hz repetition rate Nd:YAG lasers used in our experiments, we can detect ΔT≃10−3. This leads to a sensitivity to optical path length changes of λ/103 for the Z-scan and λ/104 for the EZ-scan where λ is the wavelength. This interferometric sensitivity, using a single beam, allows measurement of nonlinear refraction in thin films without the need for using a waveguiding geometry.