Research On Micro-displacement Measurement Based On Heterodyne Interferometry Of Vortex Beams

As a light field with spiral wavefront phase and center phase singularity,there is fringe furcation phenomenon in the interferogram of vortex beam,which gives the vortex beam unique interference characteristics to make the interference images have high contrast.With the continuous improvement of the theory of vortex light,more and more studies have been done in the field of high-precision measurement by using the interference characteristics of vortex light.In order to meet the needs of high-precision measurement in the field of machining and manufacturing,It is of great significance to apply vortex light to the research of micro-measurement,which can promote the development of vorticity research and optical non-contact measurement.Based on the interference characteristics of vortex light and the advantages of heterodyne interferometry,in this paper,the application of vortex light and heterodyne interferometry in measuring the micro-displacement of moving objects is studied.According to the interference theory of double vortex beams,an experimental scheme of heterodyne interference about double vortex beams based on second Bragg diffraction is designed.In the scheme,the vortex beam,which generated by the liquid crystal spatial light modulator,is divided into reference beam and measurement beam by beam splitter prism,and the two beams have different frequencies after the twice Bragg diffraction modulation of acoustic optical modulators respectively,at the same time the measuring beam carries the micro-displacement information of the moving object.Heterodyne interference occurs when two beams are combined.In order to obtain the displacement information,images captured by the camera are processed using normalized cross-correlation algorithm and the difference frequency in the interferograms is extracted,and then the motion velocity of the object is calculated according to the Doppler frequency shift.Finally,the motion displacement of the object is calculated according to the camera acquisition time.In order to obtain higher measurement accuracy,the gray scale of the spatial light modulator was measured and corrected before the experiment to confirm the direction of Doppler frequency shift and the parameters of vortex light.On this basis,the motion of piezoelectric ceramics is measured and calculated by using the scheme designed in this paper,which verifies the rationality and accuracy of the design scheme,and realizes the research of micro-displacement measurement of heterodyne interferometry based on vortex light.