Spatial coherence measurement of supercontinuum generation in graded-index multimode fibers in the anomalous dispersion regime

We experimentally characterize the spatial coherence of supercontinuum light generated in graded-index multimode fibers. Using a wavefront folding interferometer, we measure the spatial coherence under varying pump powers and fiber lengths. Significantly, although the spatial intensity distribution appears to be near-Gaussian, we observe that the corresponding spatial coherence degrades with increasing power due to the excitation of higher-order modes. We also observe that spatial coherence improves with longer fiber lengths, where spectral broadening saturates and Raman-mediated modal redistribution stabilizes. Our results provide important new insights into the interplay between nonlinear dynamics and spatial coherence in multimode fiber systems, with implications for designing spatially coherent high-brightness broadband light sources for imaging, sensing, and beam combining applications.