Development of null test measurement system of aspherical mirror shape by scatter plate interferometer

大型天文望远镜主镜为凹面旋转对称非球面。望远镜的性能很大程度上取决于反射镜的形状精度，传统的干涉仪作为测量光学系统表面形状和/或光学系统特性的一种方法，得到了广泛的应用。但是，采用传统的干涉仪（如Twyman-Green干涉仪）测量深非球面时，会产生大量干涉条纹，条纹间距很窄，为了克服这些缺陷，需要采用计算全息（CGH）或特殊光学元件。但这些干涉仪本质上都是异光路干涉仪，不能用于大口径、长曲率半径的非球面，对于这类表面的干涉测量，共光路干涉法是必然的。因此，本研究的目的是研制零检测散射板干涉仪， 关于我们 本文介绍了一种用于测量旋转对称深凹非球面的干涉仪，散射板干涉仪是共光路干涉仪的一种，其零位检测原理如下。使用具有点对称特性的具有较大孔径尺寸的散射板，并且在远离散射板的后面的位置处设置针孔。在这种光学装置中，参考波前变成非球面的，并且可以使其几乎等于从被测的非球面凹面镜反射的波前。波带片干涉仪也是一种共光路干涉仪，用波带片代替散射板，可以把特制的波带片等效为散射板。比较了散射板与波带板干涉仪的关系。在此基础上，提出并实现了两种可应用于共光路干涉仪的条纹扫描技术。最后，建立了计算机控制的条纹图采集与分析系统。少

Main-mirror of big astronomical telescope has concave and rotationally symmetric aspherical shape. The performance of the telescope is greatly influenced by the precision of the shape of the mirror.As a method for measuring the surface shape and/of the characteristics of optical systems, conventional interferometers have been widely used. But, if the conventional interferometer such as Twyman-Green one is used, many interference fringes generate and the interval of fringes becomes very narrow when deep aspheric surface is measured.For overcoming these defects, computer generated hologram ( CGH ) or special optical elements are used. But these interferometers are fundamentally different-path interferometers, and can not be used for aspheric surfaces with large aperture-size and long radius of curvature.For the interferometric measurement of these surfaces, the common-path interferometric method is inevitable. So, the purpose of this research is to develop null-test scatter-plate interfe … More rometer for measuring concave deep aspheric surfaces with rotationally symmetry.The scatter-plate interferometer is one of common-path interferometers, and the principle of null-test by this interferpometer is as follows. A scatter-plate with larger aperture size of which characteristics are point-symmetry are used and a pinhole is set apart from the position behind the scatter-plate. In this optical set-up, the reference wave-front becomes aspheric and can be made almost equal to the wave-front which is reflected from the aspheric concave mirror under test. As a result, null-test can be realized.A zone-plate interferometer is also common-path interferometer and a specially optically made zone-plate can be regarded as equivalent with a scatter-plate when the zone-plate is used in the above mentioned interfero-meter instead of the scatter-plate.In this researh, at first, the priciple of null-test on scatter-plate interferometer is made clear, and next, the relation between the scatter-plate and the zone-plate interferometer is compared. Then, two kinds of fringe-scanninig techniqes which can be applied to common-path interferometer are developed and practised. And finally, computer-controlled fringe pattern aquisition and analysis system is constructed. Less