Research On Dynamic Detection Methods Of Phase Defects In Optical Elements

Driven by the demands of energy technology,national defense and military affairs,the research of high power laser devices is developing rapidly,and the usage of high precision optical elements is increasing significantly,which puts forward stricter requirements for the detection of phase defects in optical elements.Most of the phase defect detection schemes are difficult to resist environmental vibration and identify the type of defects.To realize the dynamic detection of phase defects,two schemes are proposed:(1)low-coherence dynamic Twyman interferometer based on several phase shifting interferograms,(2)reflective point diffraction interferometer based on single linear carrier frequency interferogram.To solve the problem of defect type discrimination,a defect type criterion based on lensless imaging algorithm is proposed.The research work mainly includes:Firstly,to solve the problem of environmental vibration in phase defect testing,the low-coherence dynamic Twyman interferometry and the linear carrier frequency point diffraction interferometry are proposed.The principle of polarization interferometry is studied,and the dynamic measurement of phase defects is realized by combining the low-coherence orthogonal polarization light source with instantaneous phase shifting interferometry.The principle of point diffraction interferometry is studied.The lateral shear amount is introduced between the test and reference light by the point diffraction plate,and the information of the wavefront under test is extracted from the single interferogram by FFT algorithm to realize the simultaneous measurement of phase defects.Secondly,to realize the discrimination of defect types,a theoretical model of lensless imaging based on point diffraction interferometry is constructed,and a criterion of defect type is proposed.The theory of plane wave angle spectrum is studied.A virtual image plane is constructed by setting a virtual lens,and the spherical wave propagation is transformed into the plane wave propagation,which restrains the diffraction effect of defects and realizes the discrimination of defect types.Thirdly,in order to calibrate the accuracy of the systems,a standard step is measured by the two sets of devices proposed.Compared with the measurement result of Taylor Hobson profilometer,the measurement error of low-coherence dynamic Twyman interferometer is 5.1nm,and the measurement error of point diffraction interferometer is 3.5nm,meeting the accuracy requirement.Fourthly,to verify the correctness of the proposed defect type discrimination,an amplitude defect and a phase defect in an optical flat are detected by the reflective point diffraction interferometer,and the propagation of the transmission wavefront is carried out by the lensless imaging algorithm,which verifies the correctness of the proposed defect type criterion.To simulate the phase defect,a laser damage plate and a phase plate are tested by the two proposed interferometers.Results show that the two proposed interferometers can be used to detect phase defects.Finally,the measurement error of low-coherence dynamic Twyman interferometer is analyzed.The effects of secondary diffraction and polarizer error on the measurement results are studied.The key technology and error sources of reflective point diffraction interferometer are discussed.The film system,pinhole shape and pinhole size of the point diffraction plate are designed.And the processing accuracy of FFT algorithm,the cavity error,the manufacturing error of optical elements and the experimental operation error are analyzed.