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Calcium Fluoride Plano-Convex Lenses, Uncoated
Thorlabs Ø1/2", Ø1", and Ø2" Uncoated Calcium Fluoride (CaF2) Plano-Convex Lenses offer high transmission from 0.18 µm to 8.0 μm. See the Graphs tab for detailed information about the transmission of CaF2. We also offer CaF2 plano-convex lenses with antireflection coatings for either the 1.65 µm to 3.0 µm or 2 µm to 5 µm wavelength range.
CaF2 is commonly used for applications requiring high transmission in the infrared and ultraviolet spectral ranges. Its extremely high laser damage threshold allows it to be used with excimer lasers. The material exhibits a low refractive index, varying from 1.35 to 1.51 within its usage range of 180 nm to 8.0 μm. Calcium fluoride is also fairly chemically inert and offers superior hardness compared to its barium fluoride, magnesium fluoride, and lithium fluoride cousins.
Plano-Convex lenses have a positive focal length and approach best form for infinite and finite conjugate applications. These lenses focus a collimated beam to the back focus and collimate light from a point source. They are designed with minimal spherical aberration and have a focal length which can be calculated using a simplified thick lens equation:
f = R/(n-1)
where n is the index of refraction and R is the radius of curvature of the lens surface.
Below is the transmission curve for CaF2. Total Transmission is shown for a 10 mm thick, uncoated sample and includes surface reflections. Each of these unmounted CaF2 plano-convex lenses can be ordered uncoated or with either of the following broadband AR coatings: 1.65 - 3.0 μm (Designated with -D) or 2 - 5 μm (Designated as -E).
Wavelength-Dependent Focal Length Shift
The paraxial focal length of a lens is wavelength dependent. The focal length listed below for a given lens corresponds to the value at the design wavelength (i.e., the focal length at 588 nm). Since CaF2 offers high transmission from 0.18 - 8.0 µm, users may wish to use these lenses at other popular wavelengths. Click on the graph icons below to view theoretically-calculated focal length shifts.
Ø1/2" Plano-Convex CaF2 Lenses, Uncoated
Ø1" Plano-Convex CaF2 Lenses, Uncoated
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.