Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.
Opt Lett. 2010 Jul 15;35(14):2346-8. doi: 10.1364/OL.35.002346.
Surface measurements of precision optics are commonly made with commercially available phase-shifting Fizeau interferometers that provide data relative to flat or spherical reference surfaces whose unknown errors are comparable to those of the surface being tested. A number of ingenious techniques provide surface measurements that are "absolute," rather than relative to any reference surface. Generally, these techniques require numerous measurements and the introduction of additional surfaces, but still yield absolute information only along certain lines over the surface of interest. A very simple alternative is presented here, in which no additional optics are required beyond the surface under test and the transmission flat (or sphere) defining the interferometric reference surface. The optic under test is measured in three positions, two of which have small lateral shifts along orthogonal directions, nominally comparable to the transverse spatial resolution of the interferometer. The phase structure in the reference surface then cancels out when these measurements are subtracted in pairs, providing a grid of absolute surface height differences between neighboring resolution elements of the surface under test. The full absolute surface, apart from overall phase and tip/tilt, is then recovered by standard wavefront reconstruction techniques.
精密光学元件的表面测量通常使用市售的相移菲索（Fizeau）干涉仪进行，这些干涉仪提供的数据相对于平面或球面参考表面，而参考表面的未知误差与被测试表面相当。许多巧妙的技术提供了“绝对”的表面测量，而不是相对于任何参考表面。通常，这些技术需要多次测量并引入额外的表面，但仍然只能在感兴趣的表面上的某些线上提供绝对信息。这里提出了一种非常简单的替代方法，其中除了被测表面和定义干涉参考表面的透射平面（或球体）之外，不需要额外的光学元件。被测光学元件在三个位置进行测量，其中两个位置在正交方向上有小的横向偏移，名义上与干涉仪的横向空间分辨率相当。当这些测量值成对相减时，参考表面中的相位结构会相互抵消，从而在被测表面的相邻分辨率单元之间提供了一个网格状的绝对表面高度差。然后，通过标准的波前重建技术，可以恢复除整体相位和俯仰/偏摆之外的完整绝对表面。
