CaF2 Negative Meniscus Lenses, AR Coating: 3 - 5 µm
| Common Specifications |
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| Substrate Material | Vacuum-Grade Calcium Fluoride | | Wavelength Range | 0.18 - 8.0 μm | | AR Coating Range | 3 - 5 μm | | Reflectance over Coating Range (Avg.) | <2.0% | | Diameters Available | 1/2" or 1" | | Diameter Tolerance | +0.00/-0.10 mm | | Thickness Tolerance | ±0.1 mm | | Focal Length Tolerance | ±1% | | Surface Quality | 40-20 (Scratch-Dig) | | Spherical Surface Power* | 3λ/2 | Spherical Surface Irregularity
(Peak to Valley) | λ/2 | | Centration | ≤3 arcmin | | Clear Aperture | ≥90% of Diameter | | Design Wavelength | 4 μm |
*Much like surface flatness for flat optics, spherical surface power is a measure of the deviation between the surface of the curved optic and a calibrated reference gauge, typically for a 633 nm source, unless otherwise stated. This specification is also commonly referred to as surface fit. Features- Vacuum-Grade Calcium Fluoride Substrate
- Ø1/2" and Ø1" Versions Available
- Broadband AR Coating for the 3 - 5 μm Range
- Focal Lengths from -40.0 to -1000.0 mm
Thorlabs' Ø1/2" and Ø1" Calcium Fluoride (CaF2) Negative Meniscus Lenses, which offer high transmission from 0.18 - 8.0 μm, are available with a broadband AR coating optimized for the 3 - 5 μm spectral range deposited on both surfaces. This coating greatly reduces the surface reflectivity of the substrate, yielding an average transmission in excess of 96.8% over the entire AR coating range. See the Graphs tab for detailed information. CaF2 is commonly used for applications requiring high transmission in the infrared and ultraviolet spectral ranges. 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. Negative meniscus (convex-concave) lenses, which are thinner in the middle than at the edges and cause light rays to diverge, are designed to minimize third-order spherical aberration. When used to diverge light, the convex surface should face the beam to minimize spherical aberration. They are often used in conjunction with other lenses to increase the focal length, and therefore decrease the numerical aperture (NA), of an optical assembly.
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Shown above is a theoretical graph of the percent reflectivity of the AR coating as a function of wavelength. The average reflectivity in the 3 - 5 μm range is <2.0%. The blue shading indicates the region for which the AR coating is optimized. 
Shown above is a graph of the theoretical transmission of an AR-coated calcium fluoride plano-convex lens. The blue shaded region denotes the 3 - 5 μm spectral range where the AR coating is optimized. For this wavelength range, the measured transmission is in excess of 95%. Total Transmission of Optic (CaF2 Substrate + AR Coating)The table below gives the approximate theoretical transmission of these AR-Coated optics for a few select wavelengths in the 0.18 - 8.0 μm range. To see an excel file that lists all measured transmission values for this wavelength range, please click here. Please note that the transmission values stated for wavelengths outside of the AR coating range are approximate and can vary significantly by coating lot. | Wavelength (μm) | Total Transmission |
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| 0.2 | 0.210 | | 0.4 | 0.361 | | 0.6 | 0.284 | | 0.8 | 0.453 | | 1.0 | 0.481 | | 1.2 | 0.799 | | 1.4 | 0.838 | | 1.6 | 0.641 | | 1.8 | 0.932 | | 2.0 | 0.794 |
Wavelength
(μm) | Total Transmission |
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| 2.2 | 0.733 | | 2.4 | 0.704 | | 2.6 | 0.858 | | 2.8 | 0.972 | | 3.0 | 0.977 | | 3.2 | 0.971 | | 3.4 | 0.972 | | 3.6 | 0.968 | | 3.8 | 0.962 | | 4.0 | 0.960 |
Wavelength
(μm) | Total Transmission |
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| 4.2 | 0.965 | | 4.4 | 0.972 | | 4.6 | 0.975 | | 4.8 | 0.969 | | 5.0 | 0.952 | | 5.2 | 0.927 | | 5.4 | 0.898 | | 5.6 | 0.868 | | 5.8 | 0.839 | | 6.0 | 0.815 |
Wavelength
(μm) | Total Transmission |
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| 6.2 | 0.795 | | 6.4 | 0.779 | | 6.6 | 0.767 | | 6.8 | 0.759 | | 7.0 | 0.753 | | 7.2 | 0.750 | | 7.4 | 0.749 | | 7.6 | 0.750 | | 7.8 | 0.751 | | 8.0 | 0.754 |
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Wavelength-Dependent Focal Length Shift
The paraxial focal length of a lens is wavelength dependent. The focal length listed under the Specs tab for a given lens corresponds to the value at the design wavelength (i.e., the focal length at 4 μm). Since CaF2 offers high transmission from 0.18 - 8.0 μm, users may wish to use these lenses at other popular wavelengths. Below is a table that gives the focal length (in millimeters) for each lens at fifteen popular wavelengths within the 0.18 - 8.0 μm range. The first column lists the fifteen wavelengths for which the focal length was calculated. The first row lists the item numbers. Trace across the row of choice to the column of choice to find the focal length corresponding to that lens and that wavelength. For example, the focal length of an LF5067-E negative meniscus lens when used with 488 nm light is -18.76 mm. Note that the row denoting the focal lengths at the design wavelength is highlighted in orange. Ø1/2" Negative Meniscus Lenses | LF5067-E | LF5847-E | LF5154-E |
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| 248 nm | -17.52 mm | -44.14 mm | -70.38 mm | | 405 nm | -18.56 mm | -46.62 mm | -74.44 mm | | 488 nm | -18.76 mm | -47.07 mm | -75.18 mm | | 532 nm | -18.82 mm | -47.23 mm | -75.45 mm | | 588 nm | -18.89 mm | -47.38 mm | -75.70 mm | | 633 nm | -18.93 mm | -47.48 mm | -75.86 mm | | 780 nm | -19.02 mm | -47.70 mm | -76.22 mm | | 850 nm | -19.06 mm | -47.78 mm | -76.34 mm | | 1064 nm | -19.12 mm | -47.94 mm | -76.61 mm | | 1310 nm | -19.18 mm | -48.08 mm | -76.84 mm | | 1550 nm | -19.23 mm | -48.20 mm | -77.04 mm | | 3000 nm | -19.61 mm | -49.08 mm | -78.49 mm | | 4000 nm | -20.00 mm | -50.00 mm | -80.00 mm | | 5000 nm | -20.53 mm | -51.25 mm | -82.06 mm | | 8000 nm | -23.40 mm | -57.99 mm | -93.15 mm |
Ø1" Negative Meniscus Lenses | LF5469-E | LF5414-E | LF5895-E | LF5515-E | LF5175-E |
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| 248 nm | -35.02 mm | -43.86 mm | -66.15 mm | -88.00 mm | -131.75 mm | | 405 nm | -37.12 mm | -46.45 mm | -69.89 mm | -93.07 mm | -139.45 mm | | 488 nm | -37.51 mm | -46.92 mm | -70.57 mm | -94.00 mm | -140.86 mm | | 532 nm | -37.64 mm | -47.09 mm | -70.81 mm | -94.32 mm | -141.36 mm | | 588 nm | -37.77 mm | -47.25 mm | -71.04 mm | -94.64 mm | -141.84 mm | | 633 nm | -37.86 mm | -47.36 mm | -71.19 mm | -94.84 mm | -142.15 mm | | 780 nm | -38.05 mm | -47.59 mm | -71.53 mm | -95.29 mm | -142.84 mm | | 850 nm | -38.11 mm | -47.67 mm | -71.64 mm | -95.44 mm | -143.06 mm | | 1064 nm | -38.25 mm | -47.84 mm | -71.88 mm | -95.78 mm | -143.57 mm | | 1310 nm | -38.36 mm | -47.98 mm | -72.09 mm | -96.06 mm | -144.00 mm | | 1550 nm | -38.47 mm | -48.11 mm | -72.27 mm | -96.31 mm | -144.38 mm | | 3000 nm | -39.22 mm | -49.03 mm | -73.61 mm | -98.11 mm | -147.13 mm | | 4000 nm | -40.00 mm | -50.00 mm | -75.00 mm | -100.00 mm | -150.00 mm | | 5000 nm | -41.07 mm | -51.32 mm | -76.90 mm | -102.57 mm | -153.91 mm | | 8000 nm | -46.82 mm | -58.41 mm | -87.08 mm | -116.39 mm | -174.96 mm |
| LF5961-E | LF5048-E | LF5807-E | LF5394-E |
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| 248 nm | -175.50 mm | -438.06 mm | -656.87 mm | -875.68 mm | | 405 nm | -185.84 mm | -464.20 mm | -696.16 mm | -928.13 mm | | 488 nm | -187.73 mm | -468.98 mm | -703.35 mm | -937.73 mm | | 532 nm | -188.40 mm | -470.67 mm | -705.89 mm | -941.12 mm | | 588 nm | -189.05 mm | -472.30 mm | -708.35 mm | -944.40 mm | | 633 nm | -189.46 mm | -473.35 mm | -709.92 mm | -946.50 mm | | 780 nm | -190.38 mm | -475.68 mm | -713.43 mm | -951.18 mm | | 850 nm | -190.69 mm | -476.45 mm | -714.59 mm | -952.73 mm | | 1064 nm | -191.37 mm | -478.18 mm | -717.19 mm | -956.19 mm | | 1310 nm | -191.95 mm | -479.64 mm | -719.38 mm | -959.13 mm | | 1550 nm | -192.45 mm | -480.91 mm | -721.30 mm | -961.68 mm | | mm 3000 nm | -196.14 mm | -490.25 mm | -735.33 mm | -980.42 mm | | 4000 nm | -200.00 mm | -500.00 mm | -750.00 mm | -1000.00 mm | | 5000 nm | -205.25 mm | -513.29 mm | -769.98 mm | -1026.68 mm | | 8000 nm | -233.51 mm | -584.81 mm | -877.55 mm | -1170.28 mm |
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Additional Negative Meniscus Lenses
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CaF2, Negative Meniscus, AR Coated
