Mirrors are commonly used elements in optical systems. They can: reflect whole or only part of the beam, create real and imaginary pictures of the objects, create reversed or upright images, magnify, diminish or leave unchanged size of the image in comparison to the object,
be better in some optical systems than refractive elements (lenses) due to e.g. lack of chromatic aberration.
Solaris Optics produces mirrors on different shapes of substrates made of different kind of materials like commonly used BK7 or Zerodur. Coatings can be metallic or dielectric and designed for many spectral ranges all depends on requirements.