Original English Title: photospin multiplexing metasurface for switchable spiral phase contrast imaging
Corresponding author: Xu Ting, Nanjing University
Author: Pengcheng Hu, Cheng Zhang, Wenqi Zhu, Mingze Liu, Song Zhang, Si Zhang, Lu Chen, Henri J. lezec, Amit Agrawal, Yanqing Lu, Ting Xu*
As the two most representative working modes in optical imaging system, open field imaging and phase difference imaging can extract different shape information of objects, so developing a miniaturized, low-cost imaging system that can switch between these two important working modes is very attractive for many practical applications, such as biomedical imaging, surface defect detection, artificial intelligence target Identification, etc.
For this reason, the research team of Professor Xu Ting of Nanjing University proposed and proved that an imaging system composed of a Fourier transform device and a super structured surface spatial filter can perform two-dimensional spatial difference operation, so as to achieve isotropic edge enhanced phase difference imaging. As shown in Figure 1, the super structured surface space filter consists of a set of rectangular titanium dioxide sub wavelength nanostructures, which can provide two optical spin dependent and mutually independent phase planes in the whole visible light range. By designing and embedding the super structure surface space filter on the focal plane of the Fourier transform device, the system can realize the dynamic switch between the open field imaging mode and the phase difference imaging mode only by changing the spin state of the incident light.
Figure 1. All dielectric superstructure surface space filter
In order to demonstrate the actual function of the imaging system, the research team first used a standard resolution test version (1951usaf) as the imaging target, and used different wavelengths of supercontinuum laser to illuminate. For the left-handed incident light with wavelengths of 480 nm, 530 nm, 580 nm and 630 nm, the first line of Figure 2 shows the bright field image of the fourth group of structures in the resolution test version. These results correspond to the imaging effect of the constant phase function M1 applied by the hyperspace filter. When the polarization state of the incident light changes from left to right, the second line of Figure 2 shows the edge enhanced phase difference image of the same target test area, which corresponds to the imaging effect of the spiral phase function M2 applied by the super structure surface space filter. Regardless of the direction, the contrast of all image edges will be enhanced, which shows that the phase difference imaging mode is isotropic.
Figure 2. Open field imaging and phase difference imaging of resolution test plate under the condition of left and right incident light
One of the main advantages of phase contrast imaging is that it is easy to detect samples with small refractive index differences from the environment, such as biological cells. Therefore, the team further demonstrated the switchable imaging of the unstained onion epidermal cells with a 20 × objective lens. The first line of Fig. 3 is the light field image of onion epidermal cells collected under the left-handed incident light with wavelengths of 480 nm, 530 nm, 580 nm and 630 nm, respectively. Although some organelles can be seen in the cell, the small amplitude and phase differences between the cell wall and cytoplasm make it difficult to distinguish the boundary of a single cell. However, in the phase difference imaging mode of the right-handed incident light, the situation has changed completely, and the result is shown in the second line of Fig. 3. The contrast image after edge enhancement shows more details of cell epidermis, which makes the single cell contour easier to be recognized, which is very helpful for cell morphology observation. Combined with the advantages of planar structure, ultra-thin thickness and high pixel density, this method may open up new application scenarios in the cross field of imaging and microscopy.
Figure 3. Open field imaging and phase contrast imaging of unstained onion cells under left and right incident light
This achievement was recently published on nano letters. Professor Huo Pengcheng, a doctoral student in the school of modern engineering and Applied Sciences of Nanjing University, is the first author of the paper. Professor Xu Ting is the corresponding author of the paper. His work has been carefully guided by Professor Lu Yanqing. Nanjing University is the first unit of the paper. The cooperative units include Huazhong University of science and technology and the National Institute of standards and technology of the United States.
Original text (scan or long press QR code, and then go to the original page after identification): photospin multiplexing metasurface for switchable spiral phase contract imagingpengcheng Hu, Cheng Zhang, Wenqi Zhu, Mingze Liu, Song Zhang, Si Zhang, Lu Chen, Henri J. lezec, Amit Agrawal, Yanqing Lu, Ting Xu * nano lett., 2020, DOI: 10.1021/acs.nanolett.0c00471Publication Date: March 10, 2020Copyright ? 2020 American Chemical Society
Introduction to corresponding author
Xu Ting, professor and doctoral supervisor of Nanjing University. He is the national high-level talent candidate and the leader of Jiangsu Province's entrepreneurship and innovation team, and now he is the vice chairman of the optical manufacturing Special Committee of China Optical Society. In recent years, he has published more than 50 papers in nature, nature and science journals, advanced materials, nano letters, ACS Nano, light: Science and applications, Laser Photonics reviews and other professional journals, and won the first prize of technological invention of Chinese electronic society.
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