A Method For Testing Aspheric Surface Using Computer Generated Hologram Based On Liquid Crystal Spatial Light Modulator

Aspheric surface has many excellent properties compared to the sphere, like enlarging the field of view of the system, improving the uniformity of illumination, enlarging the relative aperture of optical system, increasing the degree of freedom of optical design, improving imaging quality. At present, the processing and manufacturing technology of aspheric surface is becoming more and more mature, but the detection level is lagging behind which hindering application of aspheric surface.A method for testing aspheric surface using Computer Generated Hologram based on Liquid Crystal Spatial Light Modulator using characteristics of Liquid Crystal Spatial Light Modulator to reconstruct the 3D wavefront in real time is presented by analyzing the advantages and disadvantages of the non spherical surface inspection methods. Firstly, the measurement scheme is determined. The sequence pattern and the non sequential pattern of the proposed measurement method using ZEMAX are carried out to verify the feasibility of the method. The measurement of optical path and the optical elements are designed by means of ray tracing. The aspheric mirror with 52 mm and 50 mm, the imaging lens and compensation mirror in the optical path are designed according to the measurement scheme. The experimental device and based on Twyman Green interference principle is built to carry out experimental procedure and analysis. The wave aberration generated by a liquid crystal spatial light modulator is a reference light.In order to improve the measurement accuracy and the measurement efficiency, a kind of single interferogram analysis method is proposed: the circular domain interference pattern is extended based on the continuation method based on the sample region matching. The wrapped phase map is obtained by using the two-dimensional positive and inverse Fourier transform of the rectangular domain. Finally, the measurement results are obtained by the method of error separation. Compared the measured results with the ZYGO interferometer and the experimental results are obtained. The measurement scheme is proved to be capable of measuring the aspheric surface. Measurement error P-V value less than 1.4 ?, RMS value less than 0.7 ?.The verification of the experiment of tracing and measuring by ZEMAX, It shows that it is an efficient, real-time and universal method to detect the aspheric surface based on the liquid crystal spatial light modulator. The method reduces the requirement of the anti vibration of the environment disturbance and the test bench. Although the measurement accuracy is needed to be further improved, the method has great application prospects for the on-line detection of the aspheric mirror.