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UV Fused Silica Bi-Concave Lenses, Uncoated
Lens Kits Available
Thorlabs' UV Grade Fused Silica Bi-Concave Lenses are available either uncoated or with a UV antireflection coating for the 245 - 400 nm range deposited on both surfaces. UV-grade fused silica offers high transmission in the deep UV and exhibits virtually no laser-induced fluorescence (as measured at 193 nm), making it an ideal choice for applications from the UV to the near IR. In addition, UV fused silica has better homogeneity and a lower coefficient of thermal expansion than N-BK7.
Bi-concave lenses have negative focal lengths, making them useful for a wide range of applications. They are often used to increase the divergence of a converging beam. In optical systems, it is common for researchers to choose their optics carefully so that the aberrations introduced by the positive- and negative-focal-length lenses approximately cancel. Others use these lenses in pairs to increase the effective focal length of a converging lens.
When deciding between a plano-concave lens and a bi-concave lens, both of which cause the incident light to diverge, it is usually preferable to choose a bi-concave lens if the absolute conjugate ratio (object distance divided by image distance) is close to 1. When the desired absolute magnification is either less than 0.2 or greater than 5, the tendency is to choose a plano-concave lens instead.
Thorlabs offers bi-concave lenses in sizes ranging from Ø6 mm to Ø1". Each size is compatible with a multitude of Thorlabs lens mounts. Please see the Mounting Options tab for details.
Mounting High-Curvature Optics
Thorlabs' retaining rings are used to secure unmounted optics within lens tubes or optic mounts. These rings are secured in position using a compatible spanner wrench. For flat or low-curvature optics, standard retaining rings manufactured from anodized aluminum are available from Ø5 mm to Ø4". For high-curvature optics, extra-thick retaining rings are available in Ø1/2", Ø1", and Ø2" sizes.
Extra-thick retaining rings offer several features that aid in mounting high-curvature optics such as aspheric lenses, short-focal-length plano-convex lenses, and condenser lenses. As shown in the animation to the right, the guide flange of the spanner wrench will collide with the surface of high-curvature lenses when using a standard retaining ring, potentially scratching the optic. This contact also creates a gap between the spanner wrench and retaining ring, preventing the ring from tightening correctly. Extra-thick retaining rings provide the necessary clearance for the spanner wrench to secure the lens without coming into contact with the optic surface.