Semi-insulating GaAs provides an alternative to ZnSe in medium and high-power CW CO2 laser systems for lenses and rear mirrors. GaAs is particularly useful in applications where toughness and durability are important. Its hardness and strength make GaAs a good choice where dust or abrasive particles tend to build up or bombard the optical surface. Softer substrates allow particles to imbed in the optic even when the best coatings are used.
GaAs is manufactured for semiconductor applications rather than optical applications, so careful material screening is vital in producing quality GaAs optics.
GaAs optics are limited by crystal growth technology to diameters typically less than 10 cm. The material is non-hygroscopic, safe to use in laboratory and field applications, and chemically stable except when contacted with strong acids.