Method for real-time measurement of the nonlinear refractive index

In this work, we propose a novel method for continuous real-time measurement of the dynamics of the nonlinear refractive index n2. This is particularly important for characterizing phenomena or materials (such as biological tissues, gases, and other compounds) whose nonlinear behavior or structure varies rapidly with time. The proposed method ingeniously employs two powerful tools: the spectral broadening induced by self-phase modulation and the real-time spectral analysis using the dispersive Fourier transformation. The feasibility of the technique is experimentally demonstrated, achieving high-speed measurements at rates of several megahertz.