A plano-concave lens has one concave surface and one flat surface, with a negative focal length. It is commonly used for beam collimation, increasing (or decreasing) the focal length, or expanding (or reducing) the image. To minimize spherical aberration, when the incident beam is collimated, it should be directed onto the concave surface of the plano-concave lens. Because N-SF11 has a low Abbe number, LBTEK chooses to use N-SF11 to manufacture lenses with smaller focal lengths. Additionally, N-SF11 lenses are more suitable for particularly harsh (acidic and alkaline) environments. Apart from N-SF11 plano-concave lenses, LBTEK also offers plano-concave lenses made of N-BK7, UV fused silica, and calcium fluoride. N-BK7 is the most commonly used material for high-quality optical components, widely applied in visible and near-infrared applications. UV fused silica exhibits excellent transmittance in the ultraviolet range and a low thermal expansion coefficient, while calcium fluoride has an extremely high damage threshold and chemical inertness. LBTEK provides uncoated plano-concave lenses as well as lenses with three types of anti-reflection coatings: 400-700 nm, 700-1100 nm, and 1100-1650 nm. All our lenses undergo fine processing and strict quality control to ensure that LBTEK delivers high-quality lens products to customers at reasonable prices.