Measurement of nonlinear refractive index in open-aperture Z-scan experiments

Abstract

We present an experimental study on measurement of nonlinear refractive index (n 2) of organic liquids when the thermo-optic effects manifest into large nonlinear phase shifts (Δϕ 0) in an open-aperture Z-scan configuration. Although we do not obtain the familiar peak–valley normalized transmittance curve as in the case of closed-aperture Z-scan technique, we use a theoretical model using Gaussian beam decomposition (GD) technique to estimate the value of n 2. Using this recipe, we obtain the nonlinear refractive index n 2 = −(4.90 ± 1.20) × 10−15 cm2/W for toluene (organic solvent) and n 2 = −(10.60 ± 2.10) × 10−15 cm2/W for an organic polymer solution (10−4 M in toluene). By carrying out absorption measurements directly with an unfocussed Gaussian beam, we found nonlinear absorptions β tol = (2.42 ± 0.20) × 10−13 m/W and β poly = (2.79 ± 0.24) × 10−13 m/W which are close to the expected results.