Overview
A biconcave spherical lens is an optical component with two inward-curving spherical surfaces, causing parallel incident light to diverge. Its negative focal length makes it ideal for applications requiring beam expansion or virtual image formation. These lenses are widely used in scientific, industrial, and medical fields due to their predictable optical behavior and compatibility with standard mounts. Manufactured from materials like BK7 glass or UV-grade fused silica, biconcave lenses are available in diameters ranging from a few millimeters to over 100 mm. Precision-ground surfaces ensure minimal wavefront distortion, critical for high-performance systems such as laser beam shaping or telescopic eyepieces.
Structure and Working Principle
The lens features symmetrical concave surfaces with identical radii of curvature, though asymmetrical designs exist for specialized applications. When light passes through, refraction at both surfaces increases the beam's divergence angle. The degree of divergence depends on the lens's refractive index and curvature. For thin lenses, the focal length (f) is calculated using the lensmaker's equation, factoring in the radii of curvature (R1, R2) and material refractive index (n). Anti-reflective coatings are often applied to reduce surface losses, especially for lasers or broadband applications.
Key Features
Biconcave lenses offer high surface accuracy (typically λ/4 or better) and low scratch-dig specifications, ensuring minimal scattering. Their symmetrical design simplifies alignment in optical systems. UV or IR coatings can be customized for specific wavelength ranges. For high-power laser use, substrates like fused silica provide low thermal expansion and high damage thresholds. Plastic variants (e.g., acrylic) are lightweight and cost-effective for consumer optics but suffer from lower temperature resistance.
Application Areas
Common uses include laser beam expanders, Galilean telescopes, and optical attenuators. In microscopy, they correct spherical aberration or serve as field lenses. Industrial systems employ them for light homogenization or as part of projection optics. Telecommunications systems use biconcave lenses to manage fiber-optic signal dispersion. In consumer electronics, they appear in smartphone camera modules for distortion correction. Custom designs cater to aerospace or defense applications like targeting systems.
Maintenance and Precautions
Store lenses in dry, dust-free environments with protective caps. Clean only with lens-grade tissues and isopropyl alcohol, wiping radially to avoid concentric scratches. Avoid touching coated surfaces directly. In laser systems, verify the lens's damage threshold matches the beam intensity. For UV applications, ensure the material (e.g., fused silica) has adequate transmission at the operating wavelength. Regularly inspect for surface degradation or coating delamination.
B2B Procurement Guide
Specify diameter, focal length, material, and surface quality (e.g., 60-40 scratch-dig). For volume orders, request test reports for surface flatness and coating performance. Lead times vary from weeks for stock items to months for custom coatings. Reputable suppliers provide ISO 10110 optical drawings and certification. Compare quotes based on batch consistency, not just price. For OEM projects, discuss prototyping options and minimum order quantities (MOQs). Consider logistics—fragile optics may require specialized packaging.
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