Several methods for the measurement of very long radius of curvature of a convex or concave spherical mirror are reviewed in this paper. These methods have relevance in the measurement of the radii of curvature of laser mirrors. The accuracies achievable with the various methods are compared and summarized.

Various optical arrangements of a double-wedge-plate shearing interferometer are presented for checking laser beam collimation. The use of moiré fringes is found to be advantageous for setting the shear fringes parallel to the direction of shear in order to obtain a well-collimated laser beam. The experimental procedure and various details of the interferometer are discussed. A brief summary of a few methods for collimation testing that use a wedge plate is also given. The accuracies achievable with shearing interferometers that use a parallel plate, a wedge plate of small angle, a double wedge having a large wedge angle, a wedge plate of large angle along with two flat mirrors, and a wedge plate having a large angle are compared and summarized.

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Radial shearing interferometers have been devised by several workers earlier. All of them were based on conventional light sources, and consequently full white light compensation was required. It is possible to devise several schemes of radial shearing interferometers ignoring the condition of white light compensation when a laser source is used in place of a conventional source. Some of these arrangements are described in the present paper.