False nonlinear effect in z-scan measurement based on semiconductor laser devices:theory and experiments

With the development of semiconductor technology,semiconductor laser devices and semiconductor laser pump solid-state laser devices have been widely applied in z-scan experiments.However,the feedback light-induced output instability of semiconductor laser devices can negatively affect the accurate testing of the nonlinear index.In this work,the influence of feedback light on z-scan measurement is analyzed.Then the calculated formula of feedback light-induced false nonlinear z-scan curves is theoretically derived and experimentally verified.Two methods are proposed to reduce or eliminate the feedback light-induced false nonlinear effect.One is the addition of an attenuator to the z-scan optical path,and the other is the addition of an opto-isolator unit to the z-scan setup.The experimental and theoretical results indicate that the feedback light-induced false nonlinear effect is markedly reduced and can even be ignored if appropriate parameters are chosen.Thus,theoretical and experimental methods of eliminating the negative effect of feedback light on z-scan measurement are useful for accurately obtaining the nonlinear index of a sample.