Research On Multi-mode Microscopic Imaging Technology Of Brightfield, Darkfield, Phase Contrast

The microscopic imaging technology has always been an important foundation for researches of the life science and the medicine. The three most commonly used imaging modes are the bright field imaging, the dark field imaging and the phase contrast imaging. The bright-field mode is able to collect low-frequency information of species and it applies to observing species with strong absorption. The dark-field mode images by capturing high-angle scattered light. It's able to collect high-frequency details of species and it applies to observing species with weak absorption and clear profiles.What's more,the phase contrast mode can make use of species' phase information and it's usually used to image transparent species. It can achieve vivo observation. These three modes complement each other and give more complete view of species. Most of time, we need to make a comprehensive use of the three modes. However, with the traditional microscopic imaging technology, every mode is based on different hardware structures and it's complicated to complete the experiments of the three modes.To solve the above problems, this paper presents a multi-mode microscopic imaging system which can get the bright-field, the dark-field and the phase contrast imaging results in real time. In the way of computational illumination, this system uses an encoded LED array instead of ordinary light source. The LED array gives light in different angles and provides flexible illumination patterns. Imaging with different illumination patterns and processing with corresponding algorithms, the system gets different results without any other hardware addition.Besides, according to the partial coherent imaging characteristic of the system, this paper gives a mathematical model of it, the core of which is the PSI window function.The process of system imaging can be treated as the process of windowed filtering for species' information. Based on the mathematical model, this paper derives a phase transport function of the phase contrast mode by using an equivalent PSI window function and a one-dimensional imaging result is calculated theoretically. The corresponding PSI window is simulated by Matlab.Furthermore, in order to get phase contrast images with higher resolution and contrast, this paper completes theoretic simulations and experimental verifications of imaging results with different illumination patterns and gets three optimization conclusions as follows: First, by dividing the bright field in different angles, the system will get species' images with details in different directions. Second, increasing the numerical aperture (NA) of the illumination (equivalent to increase system coherent ratio ?) while keep that of the objective unchanging, the resolution of imaging results can be improved. But when it increases to a critical value (? = 1), the improvement of the resolution is no longer obvious. Third, using concentric annulus illuminations do good to images phase contrast increasing.Experiments show that the system described in this paper has obtained imaging results of three modes (including images of the bright field, the dark field and the phase contrast of both left-right and up-down) successfully, which spends less than 200 ms.And that is determined by the time needed by image acquisition. The system described in this paper has a good real-time imaging performance with simple operation. It's controllable and can be further used to realize other imaging modes.