Research On Micro-nano Structure Measurement Based On Digital Holography

With the rapid development of micro-electromechanical field,micro-optics field and biological cell field,micro-structure fields such as precision machining,biological cell observation,optical component detection,and nanotechnology have received more and more attention.The topography measurement work puts forward higher requirements.As a product of modern integration technology,digital holographic microscopy is a combination of traditional optical holography,photoelectric recording devices and digital image processing technology,and has broad application prospects in the field of microstructure measurement.It avoids the tedious chemical development process of traditional optical holography,records the hologram containing the amplitude and phase information of the measured object through the image acquisition device,and then uses the digital reproduction technology to obtain the three-dimensional shape of the measured object.The advantages of contactless,real-time measurement and no need to mark samples make digital holographic microscopy become the new darling of modern microscopy.The digital holographic basic optical path can be divided into an off-axis digital holographic optical path and a coaxial digital holographic optical path according to whether the object light or the reference light propagation path has an angle.The research work in this paper mainly studies the reflective and transmissive measurement work on the basis of the off-axis digital holographic optical path,and mainly completed the following work:(1)The development history of microstructure surface topography measurement technology and the development history of digital holographic microscopy technology are introduced.The development status of digital holographic microscopy technology at home and abroad is examined.(2)The basic principles of digital holography recording and imaging are expounded.Two basic experimental optical paths are introduced and the recording principle and reproduction principle are analyzed.At the same time,the three reconstruction algorithms used in the reproduction process are compared.Finally,The experimental recording conditions and related measurement principles were theoretically studied.(3)The preprocessing method of digital holographic microscopy imaging is studied.The elimination of zero-order image and conjugate image as well as the self-focusing of digital holography are discussed respectively.Based on the drawbacks of traditional frequency domain filtering,the solution of the matched filtering method is proposed.At the same time,the optimal reproduction distance of digital holography is determined by using the self-focusing algorithm.(4)The image reconstruction algorithm of digital holography is studied.The process is mainly to reconstruct the phase information.The main contents include phase unwrapping algorithm and phase distortion compensation algorithm.Firstly,the basic working principle of the two kinds of algorithms is introduced by computer simulation.Then several different methods are proposed for each type of algorithm,and the comparison of each method and the analysis of its applicable occasions are completed.(5)The reflective and transmissive digital holography experiments were carried out using the digital holographic microscopic measurement system proposed in this paper.The sample preparation process and the specific experimental flow were described in detail.The verification of various algorithms was carried out during the measurement and analysis of different types of samples.The experimental results show that the digital holographic system has good applicability for both reflective and transmissive samples,and the measurement results of the USAF1951 standard resolution test board was also verified on a laser confocal microscope to further confirm the reliability of the digital holography system.