Absolute surface figure measurement of aspherical surfaces with diffracted wavefronts as reference waves emitted from two optical fibers

在这一年里，我们致力于防止PS/PDI系统相移干涉测量中产生的多余干涉条纹。用于PS/PDI的干涉条纹被投射到光纤板(FOP)上。FOP用于将干涉条纹从前表面转移到后表面。FOP由大量捆绑在一起的光纤组成。在FOP背面，转移干涉条纹的相干性降低。因此，条纹的CCD图像不包含因光学端面反射而产生的多余的条纹或图案。通过使用(1)带电子快门的CCD摄像机和(2)重新设计PZT工作台的移位程序，消除了振动源。在此基础上，我们尝试用两个衍射…之间的相移干涉法来估计PS/PDI系统的测量误差光纤发出更多的作用波。结果表明，在剔除(1)由FOP引起的特定图形误差和(2)由实验环境机械振动引起的条纹误差后，PS/PDI的测量误差估计为0.35 nm RMS。原则上，PS/PDI在非球面测量中不能直接给出绝对面形，因为诊断波前会产生很大的失真。因此，我们尝试使用PS/PDI结果重建绝对表面图形。根据Helmholtz-Kirchhoff积分定理，编制了一套独创的相位诊断程序。该程序利用PS/PDI的结果和样品镜上反射的诊断性球面波前的光强分布重建出非常球面的图形。在不久的将来，该方案将在抛物面等实际表面的测量中检验其有效性。较少

In this year, we have concentrated on to prevent unwanted interference fringes which occurs in phase-shifting interferometry of PS/PDI system. The interference fringes used in PS/PDI are projected on FOP (Fiber Optic Plate). The FOP is used to transfer the interference fringes from its front surface to rear surface. The FOP consists of a large number of optical fibers bundled together. Coherency of the transferred interference fringes decreased at the rear surface of FOP. Therefore CCD image of the fringes did not contain the unwanted fringes or patterns caused by end reflection of optics. Source of vibration was removed by using (1) CCD camera with electronic shutter, and (2) redesigning of shifting program for PZT stage. As a result, repeatability of concave mirror (diameter:200mm, ROC: 1500mm) measurement was estimated to be 0.38nm rms.With the results described above, we have tried to estimate measurement error of the PS/PDI system by phase shifting interferometry between two diffr … More acted waves emitted from optical fibers. As a result, b y removing (1) specifically-patterned error caused by FOP, and (2) fringe error caused by mechanical vibration of experimental environment, the measurement error of the PS/PDI was estimated to be 0.35nm rms. This value may not decrease until we protect an emergent mechanical vibration during the measurement procedure.In principle, the PS/PDI does not give us absolute surface figure directly in the measurement of aspherical surfaces because of a huge distortion of the diagnostic wavefront. Therefore we have tried to reconstruct the absolute surface figure using the PS/PDI result. We have made an original phase diagnostic program based on Helmholtz-Kirchhoff integral theorem. This program reconstructs very spherical surface figure using the result of PS/PDI and an intensity distribution of diagnostic spherical wavefront which reflected on the sample mirror. In the near future, an effectiveness of the program will be checked in the measurement of actual surface such as parabolic reflector. Less