Study On Medium-high Frequency Errors Of Optical Elements Used In High-Power System

The laser induced damage threshold of optical elements can be reduced by medium-high frequency(MHF) errors generated from the deterministic optical manufacturing technology, and the safety of high-power laser system will be influenced. Therefore, the magnitude and distributing characteristics of medium-high frequency errors must be strictly controlled. The optical elements can be manufactured by using magnetorheological finishing technology with high accuracy, high efficiency and low damage of subsurface. But the medium-high frequency errors can easily be produced in the process of magnetorheological finishing due to the small diameter of removal function, and this will introduce the nonlinear self-focusing phenomenon and the surface damage of optical elements. The ultraprecision turning technology is suitable for manufacturing a type of optical elements used for frequency switching in high-power laser system, but the stripe errors, which need to be well identified and strictly controlled, are easily to be found on the manufactured surface after the ultraprecision turning.According to above conditions, the spectrum characteristics of wavefront errors which are from the magnetorheological finishing process or the ultraprecision turning process are evaluated and expressed by using power spectral density curves, the main contents of this paper are as follows:1) Based on the operating capabilities of high-power laser system, the special requirements of optical elements are analyzed, this will provide a reference for the evaluation on the error spectrums of optical elements used in high-power laser system.2) The calculation methods of power spectral density on wavefront errors are studied, the influences of quad-flip method and window function are analyzed on the magnitude and the distribution of power spectral density, the errors located on the edges are supressed in the process of calculation, and the evaluating model on error spectrums is established.3) According to the error generating mechanism of optical elements in the process of magnetorheological finishing, the spectral characteristics of periodic errors with small scale are analyzed by using the power spectral density model, and the relationship is discovered between the processing parameters and sensitive frequency errors.4) On the basis of the analysis of error features from the ultraprecision turning process, the influences of machining parameters such as the amount of feed, the spindle speed and the cutting depth are studied on the error spectrums, and this helps to control for medium-high frequency errors and choose the optimal manufacturing parameters in the process of ultraprecision turning.