Mirrors are optical devices that reflect light. Reflection only happens when the angle of reflection equals the angle of incidence. They are designed to reflect light for a variety of applications, including beam steering interferometry, imaging, or illumination. They are optimized for the proper wavelengths and are also designed for lasers, the damage thresholds that are suitable for the designated laser. Their surfaces do not need to be flat, as curved surfaces (convex or concave) can be used as reflectors as well.