Research On Adaptive Phase-Shifting Interference Detection System Based On Wavelength Tuning

With the development of science and technology,optical components have been widely used in various fields.In addition to increasing accuracy requirements,the size of components is also gradually increasing.Phase-shifting laser interference is the main method for surface topography detection of optical components.Because wavelength-tuning phase-shifting interference technology does not need to move the reference mirror inside the interferometer during the detection process,it has higher stability and is often used as large-aperture optics.The main detection method of the component.The wavelength-tuning laser interferometer generally adopts the Fissau-type interference structure.In the detection process,the interferometer tunes the laser wavelength by changing the input voltage,and then changes the optical path difference between the reference light and the test light to obtain multiple frames with equal phases Interferogram of difference.The interferogram contains the wavefront information of the detection element.The least squares iterative algorithm is commonly used to resolve the phase from which the wavefront phase is calculated,and the topography information of the optical element is obtained by reconstructing the wavefront.The least squares iterative algorithm requires the accurate value of the cavity length to calculate the phase shift,which is used as the initial quantity to iteratively fit to obtain a more accurate wavefront phase distribution.However,this method needs to accurately calibrate the cavity length for each measurement,and when the contrast between the interferograms is inconsistent or the phase shift is in a special interval,the accuracy and robustness of the algorithm are greatly reduced,so use it directly This algorithm will be difficult to meet the actual detection requirements for the phase solution calculation.After studying the principle of wavelength tuning and phase shifting in depth,this paper proposes a new adaptive wavelength tuning and phase shifting algorithm.In this paper,the least squares algorithm is improved first,and contrast parameters are added in the iterative solution process,which solves the problem of large errors when there are contrast differences between the interferograms.At the same time,in order to ensure the accuracy of the dephase algorithm,a phase shift of π/2 is used in the phase shift process to perform phase shift interference.According to the principle of laser wavelength tuning,the laser voltage tuning amount and the interference cavity length are determined when the phase shift is fixed.The relationship is inversely proportional,and the mathematical model is improved through experimental data,and the calibration curve of step voltage and interference cavity length is obtained.In the detection process,firstly,the step voltage in the phase shifting process is determined according to the coarse calibration value of the cavity length and the calibration curve,and then the standard deviation value of the phase shift amount of all pixels is counted to determine the shift during the phase shift calibration process.Phase quality,to avoid mistaking phase shifting into the subsequent image processing process.When the result of the phase shift cannot meet the calculation requirements,combine the wavelength tuning characteristics of the laser to calculate the voltage compensation amount and control the phase shift amount in a reasonable range.Finally,the calibration result of the phase shift is used as the initial value of the least squares iteration,and the contrast compensation is calculated in the phase calculation process.Through iteration and optimization,the phase calculation accuracy is greatly improved.In addition,this article designed multiple sets of simulation experiments to verify the effectiveness of the algorithm under the conditions of different cavity lengths,different phase shifts and inconsistent contrast between interferograms,and this article compiled a wavelength-tunable laser interference based on the algorithm described.Instrument control software.This laboratory uses the G60U upright interferometer as the main frame.On this basis,the New Focus wavelength tuned laser is used as the phase shift unit,and the Basler area scan camera is the imaging system.A phase shift interferometer test system is independently built.The center wavelength of the semiconductor laser used in the system is 635nm,the cavity length of the interferometer system is adjustable from 10-70cm,and the minimum voltage change of the digital-to-analog(D/A)converter is 0.001v.The experiment uses a standard flat mirror with a diameter of 60mm(PV value better than λ/20)as the test object.The test results show that the PV value measurement accuracy can reach λ/20.The repeatability of PV and RMS is λ/50 and λ/1000 respectively.