Risley prisms

Summary

Risley prisms are a beam steering device comprising two thin wedge prisms mounted coaxially and rotated independently about the optical axis. By varying the relative rotation angles of the wedges, the device deflects an incident beam to any azimuth within a cone whose half-angle is set by the prism wedge angles and glass refractive index. Risley pairs are used for beam steering and pointing in applications such as free-space laser communications, tracking, scanning and imaging lidar, and in ophthalmic instruments for variable prism testing of ocular alignment.