| Micro-nano technology is a great product in the field of precision,and has penetrated into the life and production of the people from all directions.Structures often determine functionality,and objects under micro-nano technology are more sensitive to performance changes caused by structural changes because of their smaller size.With the growth of industrial production,medical life and other needs,people have put forward higher requirements for the measurement of the microscopic world.Common microscopic measurement techniques such as atomic force microscopy,field-of-use microscopy have the disadvantage of possible contact damage and the special properties of the sample.Digital holographic microscopy is a kind of interference microscopy technology,which has the advantages of contactless and global measurement.The research work in this paper mainly focuses on off-axis digital holographic microscopy technology,mainly completing the following work:(1)The generation and development of holography and digital holography were investigated.The application of digital holographic microscopy in digital holography was introduced.The development status of digital holographic microscopy at home and abroad was examined.(2)Explain the basic principles of digital holography recording and imaging,and propose an off-axis digital holographic microscopic measurement system.The off-axis digital holographic micrometer system experimentally includes interference generation and recording device construction;digital reconstruction includes diffraction calculation of hologram,phase unwrapping,phase distortion compensation,and three-dimensional shape restoration.(3)The diffraction process of light wave transmission is studied.The common digital holographic diffraction algorithms are compared and their advantages and disadvantages are analyzed.The main problems in the application of several diffraction algorithms are analyzed.At the same time,the phase unwrapping algorithm of two different integration methods is studied.Several methods of device compensation and digital phase distortion compensation are studied and compared.Then a general polynomial value compensation method after unwrapping is proposed.(4)Based on the principle of laser Michelson interference,the digital holographic microscopic optical path is designed and amplified,and an improved pre-amplification optical path based on the reference objective is proposed.(5)The USF resolution plate of the US military was tested and verified by the off-axis digital holographic micro-measurement system proposed in this paper.The operation process of specific off-axis interference and the experimental steps of reference objective adjustment were introduced in detail.Calculate the acquired hologram and calibrate it using the properties of the resolution board itself.The experimental results show that the lateral resolution of the sample reconstruction results is better,the longitudinal error is 5 nm,and the accuracy is relatively accurate.Finally,the off-axis angle is fixed,the distance of each optical component is measured,and the off-axis digital holographic micrometering system is designed and built.The compact measurement system and simple operation of the entire measurement system are of great significance for microscopic measurement technology. |
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