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

大型天文望远镜的主镜具有凹面和旋转对称的非球面形状。镜面形状的精度对望远镜的性能有很大的影响，常规干涉仪作为一种测量光学系统面形和/或特性的方法得到了广泛的应用。但这些干涉仪本质上是不同路径的干涉仪，不能用于大口径、长曲率半径的非球面，对于这些表面的干涉测量，共路干涉方法是不可避免的。因此，本研究的目的是研制零测试散射板接口…散射板干涉仪是共光路干涉仪的一种，该干涉仪的零位检验原理如下。散射板采用具有点对称特征的大孔径散射板，并在散射板后面的位置上设置针孔。在该光学装置中，参考波前变为非球面，并且可以使其与被测非球面凹面镜反射的波前几乎相等。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。最后构建了计算机控制的条纹图采集与分析系统。较少

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