High‐Order Mid‐Infrared Nonlinear Topological Differentiator

ABSTRACT High‐order edge‐enhanced imaging enables precise feature localization and effective background suppression, offering a powerful tool for real‐time recognition and high‐contrast visualization. Extending this capability to the mid‐infrared (MIR) regime is particularly valuable for applications such as biomedical diagnostics, material inspection, and remote sensing, yet remains limited by inadequate spatial‐frequency modulation fidelity and low detection sensitivity. Here, we demonstrate a high‐sensitivity MIR upconversion differentiator operating at 3 , which achieves isotropic high‐order edge enhancement by optically imprinting topological complex‐amplitude patterns onto MIR Fourier components via nonlinear parametric interaction. Vortex transfer functions are precisely encoded on a phase‐only spatial light modulator to enable tunable MIR differentiation from first‐ to fourth‐ order, with real‐time switching at up to 60 Hz. Benefiting from a low‐noise upconversion process and a single‐photon‐sensitive silicon camera, the system achieves high‐contrast edge imaging under low‐light conditions. Experimental results confirm accurate edge extraction and background suppression for both amplitude and phase objects, hence underscoring its potential for noninvasive diagnostics and label‐free material analysis.