|Type||Biconcave Lenses||Material||BK7,UV FS, CaF2, ZnSe, Sapphire, BaF2, Sapphire, etc.|
|Clear Aperture||>90%||Diameter Tolerance||+0.00/-0.1mm|
|Thickness Tolerance||±0.1mm||Surface Irregularity||λ/4 @ 633 nm (λ/8 optional)|
|Concentricity||3 arcmin||Paraxial Focal Length||+/-2%|
|Chamfer||0.2mm x 45 degree|
Biconcave Lenses or Double Concave Lenses are optical lenses with two inward arched spherical faces, and the radii of curvature are equal on both sides. A double concave lens has a negative focal length and diverges a collimated light beam to the virtual focal point (that is the point at which the extension lines of the diverging light path intersect at the object side of the concave lens). The usages of Biconcave lenses are diversified, encompassing divergence of collimated or focused light beams, beam diameter modulation (e.g. Galilean beam expanders), and because of their negative focal lengths, bi-concave lenses could also be applied to cancel out the spherical aberration of optical assemblies. Due to its symmetric structure, a double concave lens works best when the conjugate ratio (object distance: image distance) is close or equal to 1:1. In such situations, the distortion, spherical/chromatic aberration, and coma could be offset as a result of the equilibrium of the lenses.
Hangzhou Shalom EO offers custom Biconcave Lenses made from various materials, including Fused Silica, BK7/N-BK7, BaF2, CaF2, MgF2, Ge, ZnSe, Sapphire, and other optical materials. The working wavelengths of lenses cover a broad region from UV to IR. Custom coating options include uncoated substrates, Broadband Anti-reflection (BBAR) coatings that cut to a significant extent the reflection (average reflection below 0.5%) over a certain wavelength range, and V-coating which provides higher transmission (average reflection below 0.25%) at a narrower range, and low-cost MgF2 AR coatings (average reflection below 1.5%). The different transmission wavelength ranges of the coatings could be selected according to your requirements. Specifications such as diameters (available from 0.8mm to 300nm), focal lengths, and the f/ number of the biconvex lenses could be tailored upon your requests, and the surface irregularities could be the conventional λ/4, or λ/8 if higher precision is demanded.