Toroidal mirror is aspherical mirror where each curvature of orthogonal two axes (horizontal and vertical one) are different. So, it is no infuluenced wavelength because of using reflection only. When a spherical mirror focuses a light from a point source, there appears astigmatism. Toroidal mirrors, however, minimize such astigmatism and make it possible to focus on a small spot. The toroidal mirror is ideal for focusing and aberration correction devices.