Image Credit: Edmund Optics | CVI Laser Optics
Laser mirrors are designed for high reflectance and durability at individual laser wavelength ranges. Laser mirrors are used on the surface of solid-state lasers including alexandrite, Nd-glass, ruby, and YAG types. They are also used in conjunction with other optical elements and components, on the surfaces of other types of lasers.
Laser mirrors are formed from a variety of materials and are usually coated with a multi-layer, low absorption, dielectric coating to facilitate reflectance. Some of the more common types of materials used include BK7 glass (borosilicate glass), copper, fused silica and UV grade fused silica, nickel, optical crown glass, and proprietary materials.
Common coatings for laser mirrors include aluminum in a variety of forms, gold, rhodium and silver.
- Bare aluminum coatings are excellent reflectors in the upper UV, visible, and near infrared. The surface is soft and must be handled with care.
- Enhanced aluminum is a multilayer film of dielectrics on top of aluminum is used to enhance the reflectance in the visible or ultraviolet region. The multilayer film also provides the handling characteristics of the protected aluminum coating.
- Protected aluminum coating is used as an overcoat to protect the delicate aluminum. This treatment provides an abrasion resistant surface while maintaining the performance of aluminum.
- Gold coatings provide consistently high reflectance in the near-IR to far-IR, and are the most widely used material in these regions. Gold however is soft and easily scratched.
- Protected gold laser mirror coatings are also available. These provide the same performance as gold coatings, with additional abrasion resistance.
- Rhodium coating has a reflectivity of approximately of 80% throughout the visible spectrum. Rhodium coated nickel is considerably more durable then glass substrates both to thermal and physical damage.
Silver coatings for laser mirrors are superior in reflectance to aluminum; however its strong tendency to oxidize and tarnish means that it must be thoroughly sealed from the atmosphere in order to avoid degradation.
The International Organization for Standardization (ISO) specifies standard ISO 11145:2006 which defines basic terms, symbols, and units of measurement for the field of laser technology.