ABSTRACT
This chapter introduces the basic principles of optical testing of surfaces. Many optical components have at least one flat surface; several of them have many. These components are part of an optical system or an instrument and directly influence its performance. The point diffractin interferometer is a common path interferometer, which is used to test large radii of curvature mirrors or surfaces using a white light or a low coherence source. The good feature of the laser unequal path interferometer is that the two arms of the interferometer can be unequal so long the coherence requirement is met. The influence of vibrations and temperature variation could be serious as the two beams travel orthogonal paths and for long radius optics, the interferometer and test optics are widely separated. Fizeau interferometer can be used to test a variety of optical components: it is as versatile as the Twyman–Green interferometer but comparatively less expensive and less sensitive to vibrations.
