Nonlinear optical properties of chalcogenide glasses: comparison between Mach-Zehnder interferometry and Z-scan techniques

To explore the potentialities of chalcogenide glasses for ultrafast optical switching, the nonlinear refractive indices of different compositions are measured. Several binary glasses as well as ternary ones have been characterized. Nonlinear measurements has been performed through a pump/probe experiment using a Mach-Zehnder interferometer coupled to a CCD camera. Nonlinear refractive index as high as 12 x 10(-18) m(2)/W have been obtained in the ternary (Ge-Se-As) system. A comparison with the nonlinear coefficients obtained with the Z-scan technique is performed, Results show that, although the order of magnitude is the same, a systematic discrepancy exists, in particular for high nonlinear absorption for which the relative error reaches up to 50%. We show that this is a consequence of the use of simplified formulas derived in the Z-scan technique. Indeed, a detailed analysis demonstrates that both techniques perfectly agree when a higher-order development is used for the determination of the nonlinear coefficient from the Z-scan technique. (C) 2001 Elsevier Science B.V. All rights reserved.