BK7 Biconcave Lenses are precision negative focal length optical components with a symmetrical dual-concave structure—featuring two identical inward-curved spherical surfaces, which is the core structural characteristic that enables their light divergence function. Fabricated from high-quality N-BK7 borosilicate crown glass, these lenses boast key features including excellent optical homogeneity, low chromatic dispersion, high mechanical stability, low internal stress, and easy precision fabrication.Designed to diverge collimated light to a virtual focal point, they are widely applied in various fields: beam expansion systems (paired with plano-convex lenses in Galilean beam expanders), optical instrumentation (spectrometers, interferometers, OCR systems), imaging systems (cameras, microscopes, projectors), laser systems (laser marking, cutting, medical lasers), and scientific research laboratory setups, serving as essential components for beam modulation, aberration correction, and focal length adjustment in multi-element optical assemblies.