Research On Design Of Multi-focus Diffraction Element And The Application In Microscopy

Microimaging system plays an important role in the development of modern biomedical.However,the optical microsystem has been facing a difficult problem for a long time: high resolution and axial measurement range cannot be achieved.Until the confocal technology was put forward,this problem has been well solved.Confocal technology can remove stray light from the non-focal plane by point illumination and a small aperture to obtain axial high resolution,and obtain depth information of the object through layer by layer scanning.This method can not only obtain high precision transverse resolution but also the 3D information of the large depth of field when the static object is observed by this method.However,since the scanning process takes a certain time,it is difficult to get clear images when observing dynamic objects.This raises another problem: How to improve the time resolution based on the high spatial resolution.The multi-focus diffraction element can form multiple foci along the axial direction,while the off-axis multi-focus diffraction element can separate multiple foci from the vertical axis.The combination of off-axis multi-focus diffraction element and microimaging system can image multiple object planes in the same image plane at the same time,so as to reduce the scanning time and improve the time resolution of the microscope.This paper focuses on the multi-focus micro imaging system,from the design and processing of key optical elements to the design and construction of the optical path of the wideband multi-focus micro imaging system,and then to the achromatic measures and experimental verification of the multi-focus microimaging system.The main contents are as follows:1.A new design method of the planar multi-focus diffraction element was proposed,and the optimization objective function of step structure was established.The design of multi-focus diffraction elements suitable for multiple working wavelengths was realized.The advantages of the new method were verified by comparing different design methods of multi-focus optical elements.The design parameters that may affect the diffraction efficiency of the planar multi-focus diffraction element were analyzed.It provided a theoretical basis for the design of multi-focus optical elements with high diffraction efficiency.2.A multi-focus microimaging system was designed and built.The multi-focus diffraction element and 4F system were combined to establish a multi-focus imaging module.The geometric parameters such as focal length and off-axis of the diffraction element were analyzed.The relationship between the lens focal length and the object distance interval in the 4F system was analyzed.The geometric parameters of the optical elements in the 4F system were determined according to the size and actual optical path of the image sensor used in the experiment;the multi-focus imaging was used to determine the geometric parameters of the optical elements in the 4F system;the multi-focus imaging was used to analyze.The module and commercial microscope system were combined to complete the multi-focus microimaging system.3.In order to improve the imaging resolution,the chromatic aberration of the non-zero diffraction order image in the multi-focus microscopic imaging system was corrected.The chromatic aberration caused by the length of the periodic linewidth of the multifocal diffractive element on the non-zero diffraction order image was analyzed,including the influence of the central periodic linewidth and the periodic linewidth at different positions of the diffractive element on the chromatic aberration;the dispersion of different optical materials on different wavelengths was calculated,and the equilateral triangular prism made of appropriate optical materials was selected to reverse the chromatic aberration caused by the diffractive element;the relationship between the angle of non-zero diffraction order incident light and the final chromatic aberration correction result was analyzed,and the optimal incident angle for chromatic aberration correction was determined.The effect of residual chromatic aberration on the resolution of the microimaging system was evaluated.The results show that the resolution reduction can be controlled within 150 nm.4.The multi-focus diffractive elements were fabricated by using the photoresist mask method.The analysis model of diffractive efficiency of multi-focus diffractive elements was established,and the machining errors that may affect the diffractive efficiency of multi-focus diffractive elements were analyzed.The uniformity of diffractive efficiency of diffractive order of multi-focus diffractive elements was analyzed.The multi-focus diffractive elements were characterized by the surface profiler and the white light interferometer.5.The imaging performance of the multi-focus microimaging system was evaluated by imaging tests.Based on the multi-focus microimaging system,the resolution plate was used to evaluate the achromatic performance of the equilateral triangular prism,and the experimental results show that the resolution reduction is 103 nm.The energy utilization ratio of the multi-focus microimaging system was tested.The actual energy utilization ratio is 79.55%,which is 92% of the theoretical value.The appropriate observation samples,such as transparent microspheres,human red blood cells,and other biological cells,were selected for real-time observation by using the multi-focus microimaging system,so as to verify the performance of simultaneous imaging of multiple objects fusion.A large depth of field and clear image can be obtained after multi-focus image fusion processing.The research work of this paper shows that the multi-focus microimaging system based on the equilateral triangular prism for color difference correction is helpful to improve the temporal resolution of dynamic object imaging.to improve the temporal resolution of dynamic object imaging.The color difference correction by equilateral triangular prism has the advantages of simple operation,high flexibility,and high utilization rate of light energy.The research work in this paper provides a theoretical and technical basis for a high temporal resolution multifocal microimaging system.