Features

• Vacuum-Grade Calcium Fluoride Substrate
• Ø1/2" and Ø1" Versions Available
• Broadband AR Coating for the 3 - 5 μm Range
• Focal Lengths from 20.0 to 1000.0 mm

Thorlabs' Ø1/2" and Ø1" Calcium Fluoride (CaF₂) Positive 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.

Positive meniscus (convex-concave) lenses, which are thicker in the middle than at the edges and cause light rays to converge, are designed to minimize third-order spherical aberration. When used to focus a collimated beam, the convex side of the lens should face the source to minimze spherical aberration. They are often used in conjunction with other lenses to decrease the focal length, and therefore increase the numerical aperture (NA), of an optical assembly. Since a positive meniscus lens has a greater radius of curvature on the concave side of the lens than on the convex side, real images can be formed.

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 LE5234-E positive meniscus lens when used with 248 nm light is 69.82 mm. Note that the row denoting the focal lengths at the design wavelength is highlighted in orange.

Ø1/2" Positive Meniscus Lenses

	LE5838-E	LE5243-E	LE5234-E
248 nm	17.47 mm	43.67 mm	69.82 mm
405 nm	18.54 mm	46.34 mm	74.11 mm
488 nm	18.73 mm	46.83 mm	74.90 mm
532 nm	18.80 mm	47.00 mm	75.18 mm
588 nm	18.87 mm	47.17 mm	75.45 mm
633 nm	18.91 mm	47.27 mm	75.62 mm
780 nm	19.01 mm	47.51 mm	76.00 mm
850 nm	19.04 mm	47.59 mm	76.13 mm
1064 nm	19.11 mm	47.77 mm	76.41 mm
1310 nm	19.17 mm	47.92 mm	76.65 mm
1550 nm	19.22 mm	48.05 mm	76.86 mm
3000 nm	19.60 mm	49.00 mm	78.40 mm
4000 nm	20.00 mm	50.00 mm	80.00 mm
5000 nm	20.54 mm	51.36 mm	82.19 mm
8000 nm	23.47 mm	58.69 mm	93.97 mm

Ø1" Positive Meniscus Lenses

	LE5183-E	LE5801-E	LE5802-E	LE5803-E	LE5382-E
248 nm	34.94 mm	43.55 mm	64.92 mm	86.98 mm	130.96 mm
405 nm	37.08 mm	46.27 mm	69.16 mm	92.46 mm	138.99 mm
488 nm	37.47 mm	46.77 mm	69.94 mm	93.47 mm	140.46 mm
532 nm	37.60 mm	46.94 mm	70.22 mm	93.83 mm	140.98 mm
588 nm	37.74 mm	47.11 mm	70.48 mm	94.17 mm	141.48 mm
633 nm	37.82 mm	47.22 mm	70.65 mm	94.39 mm	141.80 mm
780 nm	38.01 mm	47.47 mm	71.03 mm	94.88 mm	142.52 mm
850 nm	38.08 mm	47.55 mm	71.16 mm	95.04 mm	142.75 mm
1064 nm	38.22 mm	47.73 mm	71.44 mm	95.40 mm	143.29 mm
1310 nm	38.34 mm	47.88 mm	71.68 mm	95.71 mm	143.74 mm
1550 nm	38.44 mm	48.01 mm	71.88 mm	95.98 mm	144.13 mm
3000 nm	39.20 mm	48.98 mm	73.41 mm	97.95 mm	147.00 mm
4000 nm	40.00 mm	50.00 mm	75.00 mm	100.00 mm	150.00 mm
5000 nm	41.09 mm	51.39 mm	77.17 mm	102.80 mm	154.09 mm
8000 nm	46.93 mm	58.86 mm	88.92 mm	117.92 mm	176.13 mm

	LE5414-E	LE5990-E	LE5656-E	LE5714-E
248 nm	174.52 mm	437.36 mm	655.91 mm	874.98 mm
405 nm	185.26 mm	463.79 mm	695.60 mm	927.72 mm
488 nm	187.23 mm	468.62 mm	702.86 mm	937.37 mm
532 nm	187.92 mm	470.33 mm	705.43 mm	940.78 mm
588 nm	188.60 mm	471.98 mm	707.91 mm	944.08 mm
633 nm	189.03 mm	473.04 mm	709.50 mm	946.20 mm
780 nm	189.99 mm	475.40 mm	713.04 mm	950.90 mm
850 nm	190.30 mm	476.18 mm	714.22 mm	952.46 mm
1064 nm	191.01 mm	477.93 mm	716.84 mm	955.94 mm
1310 nm	191.62 mm	479.40 mm	719.06 mm	958.89 mm
1550 nm	192.14 mm	480.69 mm	720.99 mm	961.46 mm
3000 nm	195.98 mm	490.13 mm	735.18 mm	980.31 mm
4000 nm	200.00 mm	500.00 mm	750.00 mm	1000.00 mm
5000 nm	205.48 mm	513.44 mm	770.20 mm	1026.83 mm
8000 nm	234.98 mm	585.85 mm	878.98 mm	1171.31 mm