中频波前均方根(PSD1)是用来评价光学元件中频段波前质量的关键参数, 在对其进行数值计算之前, 需要对波前数据进行频率域滤波。滤波后的数据易导致待测区域内、外的数据截断, 引入较大的边缘高频误差与吉布斯噪声, 从而严重影响了计算准确度。为了减小数据截断带来的影响, 通过对边缘截断的数据做趋优填充, 减少截断区域内外的空间频率突变。通过对现有的空域预处理方法进行对比, 提出了一种四向扩展平均算法。经试验验证, 所提出的方法可以较好地还原光学元件的中频段面形, 显著提高PSD1测量准确度, 试验表明所提出的方法较标准值的误差平均值小于5%。

The root mean square of mid-spatial-frequency wavefront (PSD1) is a key parameter used to evaluate the quality of mid-spatial-frequency wavefront of optical components. Before numerical calculation, the wavefront data should be filtered in frequency domain. Because the filtered data is easy to lead to data truncation in and outside the region to be measured, large edge high-frequency error and Gibbs noise are introduced, which seriously affects the accuracy of calculation. In order to reduce the impact of truncation, this paper optimally fills the truncated data to reduce the spatial frequency mutation inside and outside the truncated region. A four-way extended average algorithm is proposed by comparing the existing spatial preprocessing methods. Experimental results show that the proposed method can well restore the mid-frequency segment surface shape of optical elements and significantly improve the PSD1 measurement accuracy, and the mean error of the proposed method is less than 5% compared with the standard value.