CAS Key Laboratory of Quantum Information, USTC, led by academician GUO Guangcan, has achieved new progress in up-conversion image detection, Prof. SHI Baosen, Associate Prof. ZHOU Zhiyuan and their collaborators firstly realize up-conversion phase-contrast image based on sum frequency generation in a quasi-phase matching nonlinear crystal, they also demonstrate the field of view enhancement in the up-conversion process by changing the phase matching condition. The main results have been published in journal “Physical Review Applied” [Phys. Rev. Appl., 11, 044013(2019)].
Spiral phase contrast image (SPCI) is a vitally important image detection technique. Conventional SPCI is realized by inserting a vortex phase plate with topological charge of 1 in the Fourier plane of the first lens in a 4f image system, which is used to perform spatial frequency multiplying between the object and the spiral phase plate, and the second lens is used to perform reverse Fourier transform to obtain the convolution of the image object and the spiral phase. Finally, in the image plane, the region that has zero intensity gradient will has zero intensity distribution and the region has nonzero intensity gradient will be highly lightened. On the other hand, the image detector working in the infrared regime has lower detection sensitivity and is more expensive than image detector working in the visible regime, to up-convert an infrared image to the visible regime and then detect it with high performance is an important way to solve those problems shown before. By combining phase contrast image technique and up-conversion detection based on nonlinear process we can realize up-conversion phase-contrast image detection. Prof. SHI Baosen and Asso. Prof. ZHOU Zhiyuan have devoted themselves into frequency conversion of structured light beam for many years. They have studied the propagation, evolution and conservation of optical vortex beam in second harmonics generation and sum frequency generation [Opt. Express 22, 20198(2014); JOSAB 32, 407(2015); Sci Rep. 4, 5650(2014)], and even they have developed the technique to realize the frequency conversion of single photon with structure [Light: Sci.& Appl. 5, e16019(2016); Phys. Rev. Lett. 117, 103601(2016)]. Recently, by applying vortex pump beam in image up-conversion and using a quasi-phase matching PPKTP crystal acting as a nonlinear medium and a spiral phase filter, they realize the up-conversion phase contrast image of an infrared illuminate intensity image. At the same time, a field of view enhancement factor of 2.1 is realized by changing the phase matching condition. The theoretical simulations based on coupling equations are in fully agreement with the experimental results.
Experimental setup (left) and results (right) for up-conversion phase contrast image. (Image by LIU Shikai)
Experimental results for field of view enhancement in up-conversion phase contrast image. (Image by LIU Shikai)
Based on the present scheme, by using a suitable designed crystal, we can easily realize the up-conversion phase contrast image in a specific infrared wavelength. By increasing the quantum conversion efficiency in the conversion process, this way will have higher detection sensitivity than the direct detection with infrared detector. The present image technique will be very promising in biological imaging, pattern recognition and infrared remote sensing.
This work is supported by the National Natural Science Foundation of China (NSFC); the National Key Research and Development Program of China; the Anhui Initiative In Quantum Information Technologies; the China Postdoctoral Science Foundation.
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