Effect of the relative variation of the refractive phase-shift to the absorptive phase-shift on the operating behavior of optical limiters

The optimal matching problem of the nonlinear refractive phase-shift and the nonlinear absorptive phase-shift in optical limiters is studied by means of the Gaussian beam Z-scan diffraction theoretical model. Optical limiting behaviors in the limits of the small nonlinear absorption and the large nonlinear absorption are examined. The Gaussian beam Z-scan diffraction theoretical mode and the method of simulating the optical limiting characteristics are presented, and typical numerical computational findings are given. Our results show that, when the nonlinear absorption of an optical limiting material is negligible, the optical limiting characteristic curve exhibits a kind of slowly attenuating oscillating waveforms. In this case, the optical limiting threshold and the clamped output value of the optical limiter are dependent on the installation position of the sample and the convergence of the incident Gaussian beam. When the phase-shift produced by the nonlinear refraction is comparable with that by the nonlinear absorption, the two optical limiting effects from the nonlinear refraction and the nonlinear absorption cancel out to some extent. Our results also show that the ratio of the nonlinear absorptive phase-shift to the nonlinear refractive phase-shift has a great impact on the optical power entering the far-field receiving aperture. To acquire a satisfactory optical limiting performance, a large enough difference must exist between the nonlinear absorptive phase-shift and the nonlinear refractive phase-shift.