An automatic focusing method for image plane digital holographic microscopic measurement

Abstract

The invention discloses an automatic focusing method used for image plane digital holographic microscopic measurement. The method comprises the following steps that a sample to be measured is moved along the main optical axis direction of an object lens and a series of equidistant holographic images are recorded; the object light intensity image corresponding to each holographic image is acquired through Fourier transform, angular spectrum filtering and inverse Fourier transform and other operation; the autocorrelation operator of each intensity image is calculated; polynomial fitting of the data changing trend of the autocorrelation operator relative to a holographic image recording position is performed, the highest point of a fitting curve is the maximum value of the autocorrelation operator, and the corresponding image position is the focusing plane position; and an electric elevating table is controlled through the programs, and the surface of the sample to be measured is moved to the position of the focusing plane so that the focused image plane holographic image can be acquired. According to the automatic focusing method used for image plane digital holographic microscopic measurement, automatic image plane holographic microscopic detection can be realized, and the surface morphology measurement method of higher accuracy and better real-time performance can be acquired.

Description

technical field [0001] The invention belongs to the field of digital holographic microscopic measurement, and more specifically relates to an automatic focusing method for digital holographic microscopic measurement of an image plane. Background technique [0002] With the development of advanced manufacturing technology, the overall size of components represented by micro-electromechanical systems (MEMS) and micro-opto-electromechanical systems (MOEMS) is getting smaller and smaller, and the surface morphology and microscopic defects of the devices have more and more influence on their performance. become more and more obvious and cannot be ignored. The most commonly used methods for surface topography measurement include mechanical probe method, optical measurement method, etc. Among them, digital holographic microscopic measurement technology (DHM), with its advantages of real-time measurement, non-contact measurement, and three-dimensional measurement, is very suitable ...

AI Technical Summary

Problems solved by technology

[0005] (1) The focusing process is carried out after the holographic image is taken, and the Fresnel hologram is used, and the resolution is not as good as the image plane hologram in theory;

[0006] (2) In the measurement after the focusing process is over, the simulation calculation of light field propagation is required for each image, which increases the amount of calculation, and the measurement speed is not as good as the image plane holography technology that does not need to perform light field propagation calculations

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