The plano-convex is the simplest lens shape. It is used in such applications as welding where achieving the smallest spot size is not critical or at relatively long focal lengths when more complex shapes would not be beneficial. A plano-convex lens should be oriented with the flat side toward the work piece and the convex side toward the laser.
Meniscus lenses have a concave curve on one side and a convex curve on the other. At relatively short focal lengths, a meniscus lens will yield a smaller focused spot than a plano-convex lens. However, meniscus lenses are more expensive to manufacture than plano-convex lenses because both sides are curved. A meniscus lens should be oriented with the concave curve toward the work piece.