Research On Large Aperture Thin Beam Auto-collimating Technology Based On Single Mode Fiber Light Source

In many science fields like synchrotron radiation sources,free electron lasers and Xray telescopes,the generated X-ray are always reflected or focused by big size mirrors who's shape error will determine the quality of light beams immediately.High precision non-contact optical inspection technique plays a pivotal role in the process of high precision machining and using of big size mirrors.LTP and NOM are the mostly used devices for inspection of large aperture mirrors,which are able to detect the surface slope by point.In order to improve the measurement accuracy,NOM uses a commercially available high precision autocollimator to replace the complex detecting light path in LTP.Since the required beam diameter of NOM is smaller than 1 mm to show the details of surface slope,while the aperture of commercially used autocollimator is bigger than 30 mm,a tiny hole diaphragm is always used to pick out the required thin light beams.For NOM is working in the mode of large aperture and thin beam,whereas autocollimator is designed for broad beam,the difference of light beam will lead to additional measurement errors.In order to satisfy the required thin beam of NOM,the research aimed at large aperture thin beam auto-collimation system was studied in this paper.In this paper,the development of autocollimator at home and abroad is introduced in detail.At the same time,the working principle of optical auto-collimation and single mode fiber light source is studied deeply.What is more important is that the specific system design is provided to realize the required technical indicators.Presented in detail,verification and design of the light source collimation system are carried out by MATLAB and ZEMAX software,the parameters of f-? lens are optimized to achieve the working mode of thin beam,the error sources that influence the measurement accuracy of autocollimator in thin beam mode are analyzed in depth and the error introduced by the incident beam divergence is analyzed by ZEMAX.Through the quantitative and qualitative analysis of error sources,influence of each error source on the system precision is clearly shown,which provides important theoretical support for the subsequent design of large aperture thin beam system.Finally,the entire large aperture thin beam auto-collimating measurement system is designed and analyzed in ZEMAX software.Results show that the measurement error of the whole system is smaller than 400 nrad with the working distance being 1-2 m and measuring range in 5 mrad,which satisfies the system's whole design greatly.