Abstract

The Eclipsing Z-scan is a variation of the well know Z-scan technique, that has been widely used for the measurement of nonlinearities in matter⁽¹⁾ When focusing a light beam onto the sample, distortions of the beam profile are induced. These distortions can be detected by measuring the light beam transmisión through an opaque disk located at the far field. By scannnig the sample around the focusing region, the transmisión changes. A peak-valley dependence is obtained from which the nonlinearity can be easily estimated with high sensitivity⁽²⁾ In this work we proposed another variation of the Eclipsing technique by locating a disk of small diameter at a distance smaller than the Rayleigh parameter. The signal is obtained by scanning the disk instead of the sample. A compact and useful formula for the calculation of the nonlinear signal is obtained using the Gaussian decomposition method. Using this technique, the thermal nonlinearity of an ethanol solutions of 1,3′-diethyl 1-2,2-quinolythiacarbocyanine iodide (DQCI) and Rhodamine 6G are measured with increased sensitivity in comparison with the usual Z-scan method. It is also shown that the nonlinear signal is proportional to the induced nonlinear refraction index for small absorption in the solution. This new method allows a simple and compact realization of the eclipsing Z-scan without affecting the technique sensitivity.

© 1996 IEEE