Research On Precise Measurement Of Large Optical Flat

Optical interferometry is based on measuring,recording and calculating of the fringes of superposed coherent beams.The regular optical measurement is relatively,which introduces a relatively deviation of the tested flat from the reference flat.When the precision of the two flat matches,an unnegligible error will be introduce,and this problem has become one of the bottleneck of manufacturing of high precision optical component.In order to solve the problems and calibrate the reference surface of large diameter interferometer with high precision,the optical absolute testing technology is needed.The absolute measurement is a decoupling calculation to the testing result,so we can get the true value of the testing flat.Firstly,the N rotation measurement is studied and improved.The physical and geometrical optics theory are deduced.The accuracy and precision of the measurements are verified.The effective elements are analyzed,including fitting number of revolution,the mechanical precision of the spinner rack etc.As a result,the number of revolution need to be over 7 times and the precision of the spinner rack should be better than 0.2°.In this way,precise measurement of large optical flatness can be realized.Secondly,oblique measurement method is studied using iterative algorithm and rotational averaging algorithm.The effective elements,like the oblique incidence angle,the mechanical precision of the spinner rack and the truncation errors have been analyzed,that the oblique incidence need to be 540 °,the precision of the spinner rack need to be better than 0.3° and the edge filling algorithm need to be adopted.Thirdly,in the absolute measurement of large optical flat,different testing results of relative measurement are compared.Then,an optimum length of C/R has got.Large amounts of tests have been taken to get the repeatability precision and the results are compared with the Skip-Flat measurement,the RMS difference of the result is lower than 0.0016?,in 100mm optical flatness measurement than S-F and the RMS difference of 300mm result is lower than0.003?,which proves the feasibility and veracity of the absolute measurements.As is shown in the passage not only the 3D shape has been recovered,but the PV and RMS is also lower than the relative measurement.Fourthly,considering the requirements of the stable environment,a physical model of the interferometer is established and the software of Ansys Fluent is used to simulate the change of the air refractive index and the temperature,which causes the undulant of the cavity.By analyzing the results and calculating the different arrangement of the C/R,we aim to provide a stable environment to the whole process.It will provide reference value for the analysis of environmental disturbance factors in practical engineering application.