Techniques for Mounting Prisms
The design of a mechanical mounting for a prism depends on a variety of factors such as the inherent rigidity of the optic; the tolerable movements and distortions of the surfaces (especially reflecting ones); the magnitudes, locations, and orientations of the steady-state forces holding the optic against its mounting reference surfaces during operation; the transient forces driving the optic against or away from those surfaces during exposure to extreme shock and vibration; thermal effects; the shape and quality of the mounting surfaces touching the optic; the sizes, shapes, orientations, and smoothness of those mounting surfaces (usually machined surfaces such as pads) on the mount; and the rigidity and long-term stability of the mount. In addition, the design must be compatible with assembly, adjustment, maintenance, package size, weight, and configuration constraints. Last, but not least, it must also be affordable in the context of the cost of the entire instrument. In this chapter, a variety of techniques for mounting prisms are described. Included are kinematic, semikinematic, and nonkinematic interfaces. Generally, prisms are rigid solid polyhedrons with flat surfaces intersecting at various dihedral angles. Some prisms, such as Porro prisms, image-erecting prisms, axicons, and cube corner prisms, may have surfaces with curved apertures that conform to rotationally symmetric transmitted or reflected beam shapes for weight reduction and packaging reasons.