Up-Conversion Imaging Processing With Field-of-View and Edge Enhancement

Spiral phase contrast (SPC) is an important and commonly used image processing technology in edge detection applications, and realization of a broader field-of-view (FOV) is a long-pursued aim in imaging systems to allow more regions of the illuminated objects to be observed. Using the image processing technologies described, we first acquire both an enhanced FOV and SPC images using second-order nonlinear frequency up-conversion from the near-infrared (NIR) spectrum to the visible spectrum in two different configurations. In addition, SPC operation and sum-frequency generation using two different wavelengths is performed simultaneously within a periodically poled potassium titanyl phosphate (PPKTP) crystal by applying a vortex filter to the pump beam. When compared with the NIR spectrum, the up-converted image in the visible spectrum benefits from the advantages of higher detection sensitivity and lower potential speckle. By optimizing the temperature of the PPKTP crystal, controllable spatial patterns of up-converted images with observation cone angle enhancement of the FOV by more than 2.1 times is realized in both configurations. Additionally, we perform numerical simulations of the above phenomenon and the results agree well with those of the experimental observations. Our results provide a very promising image processing method that may be widely used in biomedicine and up-conversion monitoring applications.