/ Toroidal Mirrors
A toroidal mirror is one with different radii of curvatures on its orthogonal axis (horizontal or vertical), which resemble the inverse of a tyre or barrel. In this manner, the astigmatism associated with shprical mirrors can be minimized.
These toroidal mirrors are generally used to form the beam after it has passed through a 90° beam bender in laser machining equipment, to correct long beamlines (THz), Schiefspiegler telescopes in astronomy (Yolo telescopes), in spectrometers as a tilted imaging mirror in place of the more sophisticated (an therefore costly) ellipsoidal mirrors, and in many other similar applications.
The manufacture of toroidal mirrors is generally less complex as equivalent off-axis spherical versions, and provides therefore, a very good alternative.