Broadband incoherent imaging recovery via nonlinear gain in photorefractive gratings

Incoherent imaging through scattering media is strongly constrained by stochastic background noise, where weak image features are easily overwhelmed. Here, we demonstrate a nonlinear amplification mechanism in photorefractive (PR) media that is selective in spatial frequency under broadband incoherent illumination. Effective multi-mode correlations dynamically inscribe a multi-frequency PR grating, thereby enabling selective energy redistribution among spatial frequency components. As a result, the effective nonlinear gain exhibits a pronounced non-monotonic dependence on spatial and temporal coherence, revealing optimal conditions for incoherent nonlinear gain.