利用数字全息测量方法结合变采样间距的衍射传输算法实现双焦点光子筛器件焦距及焦斑的同时精细测量.给出了双焦点光子筛器件及其理论焦斑分布,采用双曝光的离轴全息方法得到了CCD接收面处光场的复振幅分布, 基于此光场通过变采样间距的衍射传输算法获得具有较高分辨率的双焦点光子筛的聚焦场特征, 与CCD直接测量结果相比, 焦斑分辨率提高了10倍, 双焦点光子筛的焦距等于自动对焦算法及强度最大值扫描方式分别求得的两段距离之和.实验结果表明测得的双焦距与设计焦距偏差分别为0.53%和0.37%, 得到的两个焦斑半值全宽与设计值相比, 其偏差分别为2.86%和1.86%.本文提出的测量方法除了应用于光子筛类器件的性能检测以外, 还能够广泛应用于其它类衍射透镜聚焦特性的测量与性能分析.

The digital holographic measurement method and the diffraction propagation algorithm of variable sampling interval were proposed to realize the fine measurement of the focal length and focal spot of the photon sieve. The bifocal photon sieve and its theoretical focal spot distribution were presented. The double-exposure off-axis holographic method was used to obtain the complex amplitude distribution of the light field at the CCD. Based on the light field, the focusing field characteristics of bifocal photon sieves with higher resolution were obtained through the diffraction propagation algorithm of variable sampling interval.The resolution of the focal spot is about 10times that of the direct measurement by CCD. The focal length is equal to the sum of the two distances obtained by the autofocus algorithm and the intensity maximum scanning method respectively. The experimental results show that the deviations between the measured bifocal lengths and the designed focal lengths are 0.53% and 0.37% ,respectively. Compared with the full-width at half-maximum of Greek-ladder photon sieve as required, the measured width of the two focal spots is accurate enough with error of 2.86% and 1.86%, respectively. The measurement method proposed in this paper can be widely applied to the measurement and performance analysis of other diffractive lens focusing characteristics besides the performance testing of photon sieves.