Mirror mounts are used to hold and support mirrors of all sizes and shapes. Mirror mounting can be a very sophisticated device in optic research, due to the need to be able to tip and tilt the mirror by controlled amounts, while still holding it in a precise position where it is not being adjusted. There are many types of mirrors that are used for mirror mounts. Examples include laser mirrors, parabolic mirrors, optic mirrors, and flat mirrors. Laser mirrors are designed for high reflectance and durability at individual laser wavelength ranges and are used on the surface of solid-state lasers including alexandrite, Nd-glass, ruby, and YAG types. Parabolic mirrors offer excellent correction of spherical aberration and can be either be on-axis or off-axis. On-axis parabolic mirrors produce collimated reflected light and off-axis parabolic mirrors focus reflected light to a focal point off-axis. Flat mirrors are smooth, highly polished, flat surfaces, for reflecting light. The actual reflecting surface is usually a thin coating of silver, aluminum, or other material. Most flat mirrors are coated, and then over coated a second time to add a level of scratch resistance. Optic mirrors are commonly called front surface or first surface mirrors as the light is reflected off the coated surface without passing through the glass. Optical flats are precisely polished flat surfaced devices used as references against which the flatness of an unknown surface may be compared. When the polished surface of optical flats are placed in contact with a test surface, and viewed with a monochromatic light, an interference pattern of dark and light bands can be discerned. Other types of mirrors that can be used for mirror mounts are commonly available.