Nanosecond Z-scan measurements of optical nonlinearities in 5CB and CB15 at 532 NM

Using the Z-scan method, we study the nonlinear absorption and refraction i n the transient regime of 2 - 5-mm liquid-crystal samples in the isotropic state at 532 nm, in the absence of linear absorption. Simple model systems, pure 5CB and CB15, with identical chemical composition but conformal diffe rences, were used. The 532-nm nonlinear refractive index of these compounds was found to be 2.4 - 3.7 times in excess of that of CS2 for 7 - 8-ns puls e duration and 50 - 80-mu m beam diameter. The nonlinear absorption coeffic ient of 5CB in its isotropic state is found to be more than 6 times larger for the 125-mu m path length than for the 2-mm samples. Contributing mechan isms are discussed.