Spectrally modulated Airy beams enable the measurement of the Kerr nonlinear response

Airy beams have recently found applications in optical measurements to detect the nonlinear response of media, leveraging their unique propagation properties. However, existing approaches rely on pronounced Airy acceleration, which inhibits measurements of nonlinear response in thin media. Here, we propose a new method exploiting two-dimensional Airy beams to measure Kerr nonlinear coefficients in thin media. In this new scheme, the sample under test is placed near a cubic phase mask in the Fourier plane and illuminated by a wide Gaussian beam experiencing nonlinear self-phase modulation. The Gaussian spectrum, which can be approximated by a parabolic surface, manifests as a quadratic phase modulation in the nonlinear regime and produces a measurable displacement of the generated Airy beam. By measuring both the Airy displacement and the Gaussian peak intensity, the Kerr nonlinear coefficient of the thin medium can be directly determined. We find that tuning the Airy parameters enhances the accuracy of the method across different nonlinear strengths. Unlike the conventional Z-scan technique, our single-step approach avoids repeated light exposure and reduces the risk of laser-induced damage to the sample.