The plane convex lens has a conevx side and a plane side. which is usually used for beam alignment, decrease focal length or expand images. In order to get smaller spherical aberration, when the incident beam is collimated, the collimated beam should be incident to the convex surface of the plano-concave lens. For point light source collimation, the beam incident on the plane surface.
Plano convex lenses are usually made of several materials, N-BK7, N-SF11, ultraviolet fused silica, and CaF2, of which N-SF11 is often used to make lenses with smaller focal length, uV fused silica has a good transmittance and low coefficient of thermal expansion in the UV band, CaF2 has a very high damage threshold and chemical inertness.