Research On Thchonology Of Detecting Phase Defects Of Optical Elements Based On Phase-Shifting Interference

Inertial Confinement Fusion uses beams with high power to target, which is known as one of the most promising way to the energy crisis. The quality of optical elements with large diameter in the system is of great importance, which can affect the accuracy of system and existing defects can even cause damage. Phase defects exist widely in optical elements which can modulate the phase of light without changing the amplitude. Such defects can focus beams which will cause damage in optical elements especially in systems with high power. Since phase defects can not be detected in traditional optical methods, lots of studies have been done home and abroad and lots of methods have been proposed such as spatial filtering, digital holography and phase shifting interference. Phase shifting interference has the greatest future for its large detecting range and high accuracy. Few research has been done inland and there i s still no product.This article adopts phase shifting interference as the way to detecting phase defects in optical elements and the main content is as follows.1. The basic theory of detecting phase defects is studied. Considering errors of different phase shifting plans, the step plan with PZT is adopted. Errors introduced by PZT, laser and CCD are analyzed specifically for model selection.2. A kind of 13-frame phase extraction algorithm is developed with a method using data-sampling window. Considering the vibration with large amplitude, the Advanced Iterative Algorithm is studied. Simulation s are done on the two algorithms above and the Hariharan 5-frame algorithm. Results show that the Advanced Iterative Algorithm has high surface accuracy and the Peak-to-Valley(PV) of error is between 0.2 and 0.5nm steadily.3. Because of the phase wrapping, phase unwrapping algorithms based on least square are studied and simulations are done on some specific algorithms. Results show that phase unwrapping algorithms based on least square are not affected by outliers and the Lateral Shearing Least Square is the only choice with terrible undersampling.4. Zernike polynomials are used to correct wavefront tilt and constant. The geometry error due to the structure itself is associated with the tilt and comatic aberration so that it can be corrected. A method of circle filting is proposed to correct the excursion between Zernike coordinate and geometry coordinate.5. The laser is tested with Michelson interference and meets the requirement. The phase defect is detected with the detecting system constructed and the result is consistent to that of Confocal Microscope. The standard deviation of Peak-to-Valley(PV) and Root Mean Square(RMS) of error in 15 measurements are 17.2nm and 2.0nm.