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UV Fused Silica Plano-Concave Lenses, Uncoated
Thorlabs' UV Grade Fused Silica Plano-Concave lenses are uncoated 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.
Plano-concave lenses have negative focal lengths, making them useful for a wide range of applications. They are commonly used to diverge a collimated incident beam; in such cases the collimated light source should be incident on the curved surface to minimize spherical aberrations. Plano-concave lenses, which produce virtual images, are used as the entrance optic in Galilean-type beam expanders; this lens provides the desired divergence and then a doublet is used to recollimate the 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. Still 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 collimated incident light to diverge, it is usually preferable to choose a plano-concave lens if the desired absolute magnification is either less than 0.2 or greater than 5. Between these two values, bi-concave lenses are generally preferred.
Thorlabs offers these plano-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.