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Mid‐Infrared Single‐Photon Edge Enhanced Imaging Based on Nonlinear Vortex Filtering

Edge enhanced imaging via the spiral phase contrast enables to reveal the phase or amplitude gradients of a target, which has been proved useful in feature recognition, machine vision, and object identification. A long quest is to extend the operation wavelength into the mid‐infrared (MIR) region, as highly demanded in various fields including infrared sensing, astronomic observation, and biomedical diagnosis. Here, ultra‐sensitive MIR imaging at the single‐photon level based on nonlinear frequency upconversion is demonstrated, where the spectrally converted replica of the MIR object image at 3070 nm is captured by a silicon electron multiplying charged coupled device. The imaging sensitivity is significantly improved by the coincidence pulsed pumping with a spectro‐temporal optimization. Furthermore, the edge enhancement is realized by imprinting the spiral phase pattern of the pump onto the upconverted field at the Fourier plane within the nonlinear crystal. Such a nonlinear spatial filter not only provides an effective way to implement the required high‐fidelity vortex screening in the edge enhanced detection, but also renders the MIR illumination into a visible image in an efficient and low‐noise fashion. The presented system for MIR edge enhanced imaging might facilitate immediate applications in label‐free histopathological diagnosis and non‐destructive defect inspection.