Research On Digital Holographic Measurement Method Based On Vortex Beam

With the continuous development of micro-nano fabrication technology,micro-nano structural components such as MEMS sensors,micro-lens arrays and phase resolution plates have wide application prospects in many fields.However,its surface profile,surface defects and other parameters directly affect the use of micro-nano components,Therefore,accurate three-dimensional testing of micro-nano structures is an indispensable key link.Digital holography has the advantages of real-time,non-destructive detection and fast imaging speed.However,due to the limitation of the technical level of the optoelectronic couplers of the recording medium,some high-frequency components are missed in the process of image acquisition,which affects the quality of reproduction image and the accuracy of phase reconstruction.Vortex beam has unique optical characteristics such as annular light intensity structure and spiral phase wavefront.The precise modulation of its wavefront phase can be achieved through the light field control device.Therefore,this paper explores the application of vortex beam in digital holographic three-dimensional measurement,and carries out the research on the measurement method of digital holographic microscopy microstructure optical components,which mainly includes three aspects:(1)The phase modulation technology of vortex light field is studied.According to the propagation theory of vortex beam,the intensity change and phase structure of vortex light field with different topological charges are simulated and analyzed.From the perspective of wavefront generation,different modulation methods of vortex light field are analyzed.In view of whether the phase singularity affects the authenticity of the phase reconstruction results,the stability of the phase singularity of the integer order vortex beam during transmission is numerically simulated.The interference process between vortex object light and plane wave is simulated,and the interference image is analyzed.(2)The digital holographic microscopic measurement system based on vortex beam is constructed.The experimental results of different vortex light field modulation technologies are compared and analyzed,and the correctness of the simulation results is verified,which shows that the spatial light modulator can effectively and accurately modulate the vortex light field.On this basis,the experimental optical path of vortex beam interference is built,and the test results reflect that the phase singularity of integer order vortex beam is stable.With the advantages of Mach-Zehnder measuring optical path,the experimental system of vortex beam digital holography is designed and constructed.The continuous surface and step-type structure samples are measured respectively,and stable digital holograms are obtained.In the process of hologram phase reconstruction,the reproduction processing is carried out from the aspects of original image extraction,hologram reproduction,phase unwrapping and distortion correction.(3)Experimental research on the surface microstructure of samples is carried out.The experimental results show that under the vortex beam illumination condition,the relative error of the longitudinal vector height of the micro-lens array is 3.39%.The relative error of the longitudinal depth of the phase resolution plate is 4.08%.The aberration PV and RMS values of the MDL component are both small,which can accurately evaluate its focusing characteristics.It shows that the method studied in this paper can be effectively applied to the three-dimensional detection of microstructure components.