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

大型天文望远镜主镜具有凹形旋转对称非球面。镜面形状的精度对望远镜的性能有很大的影响。作为测量光学系统表面形状和特性的一种方法，传统干涉仪得到了广泛的应用。但是，如果使用传统的Twyman-Green干涉仪对深非球面进行测量，会产生许多干涉条纹，且条纹间距很窄。为了克服这些缺陷，采用了计算机生成全息图（CGH）或特殊光学元件。但这些干涉仪本质上是异径干涉仪，不能用于大孔径、长曲率半径的非球面。对于这些表面的干涉测量，采用共程干涉法是不可避免的。因此，本研究的目的是研制用于测量旋转对称深凹非球面的零检验散射板干涉测量仪。散射板干涉仪是共程干涉仪的一种，该干涉仪进行零值检验的原理如下：采用孔径较大且具有点对称特性的散射板，并在散射板后方设置一个针孔。在这种光学装置中，参考波前变为非球面，可以使其与被测非球面凹面镜反射的波前几乎相等。因此，可以实现零检验。带板干涉仪也是共程干涉仪，当在上述干涉仪中使用带板代替散射板时，专用光学制作的带板可视为与散射板等效。本文首先阐述了散射板干涉仪的零检验原理，然后比较了散射板干涉仪与带板干涉仪的关系。在此基础上，提出了两种适用于共程干涉仪的条纹扫描技术。最后，构建了微机控制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