Simplified Kerr refractive index measurement in the visible range using phase object contrast imaging

A streamlined method is presented for determining the nonlinear refractive index n 2 using phase objects embedded in an optical imaging configuration. The approach is particularly well suited to broadband sources such as tunable optical parametric amplifiers (OPAs), which typically exhibit non-Gaussian spatial profiles and femtosecond pulses with wavelength-dependent duration. Conventional techniques such as Z-scan require precise knowledge of intensity, pulse duration, beam waist and sample position, parameters that are difficult to control in OPA-based systems. The proposed method overcomes these constraints through a two-shot comparative measurement between a reference material (e.g., fused silica) and the sample, eliminating the need for translation stages, autocorrelation diagnostics and detailed beam characterization. By referencing the nonlinear phase shift to a well-known material, the technique removes scanning and intensity-calibration requirements, ensuring broad applicability across wavelengths and sample types. Theoretical modeling and experimental validation demonstrate high sensitivity together with a substantial reduction in experimental complexity. Results show excellent agreement with established methods, confirming the reliability of the approach. This work provides a rapid and efficient route for characterizing nonlinear optical properties in situations where conventional techniques are impractical. Supplementary Material s include data-processing scripts and numerical resources to facilitate implementation and reproducibility.