N-BK7 and N-SF11 Bi-Concave Spherical Lenses

Thorlabs' N-BK7 and N-SF11 Bi-Concave lenses are popular for many applications. They are available mounted or unmounted, either uncoated or with an AR coating. Bi-Concave lenses have a negative focal length and are best used to diverge a converging beam. Bi-concave lens can diverge a collimated beam to a virtual focus and are commonly used in Galilean-type beam expanders.