Features

• Vacuum-Grade Calcium Fluoride Substrate
• Ø1/2" and Ø1" Versions Available
• Uncoated for use in the 0.18 - 8.0 μm
• Focal Lengths from 15.0 - 200.0 mm

Thorlabs' Ø1/2" and Ø1" Calcium Fluoride (CaF₂) Bi-Convex Lenses, which offer high transmission from 0.18 - 8.0 μm, are available uncoated or with a broadband AR coating optimized for the 3 - 5 μm spectral range.

CaF₂ is commonly used for applications requiring high transmission in the infrared and ultraviolet spectral ranges. Its extremely high laser damage threshold makes it useful for use 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.

Bi-convex lenses are popular for many finite imaging applications. Both surfaces are spherical and have the same radius of curvature, minimizing aberrations in situations where the object and image distances are equal or nearly equal. As a guideline, bi-convex lenses are the best choice for minimizing aberrations if the conjugate ratio (object distance : image distance) is between 5:1 and 1:5. Outside this range, plano-convex lenses are usually preferred.

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Total Transmission of Optic (CaF₂ Substrate, Uncoated)

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 588 nm). 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 LB5766-E bi-convex lens at 488 nm is 14.90. Note that the row denoting the focal lengths at the design wavelength is highlighted in orange.

Ø1/2" Bi-Convex Lenses

	LB5766	LB5922	LB5864
248 nm	13.96 mm	18.58 mm	37.11 mm
405 nm	14.75 mm	19.66 mm	39.32 mm
488 nm	14.90 mm	19.86 mm	39.72 mm
532 nm	14.95 mm	19.93 mm	39.86 mm
588 nm	15.00 mm	20.00 mm	40.00 mm
633 nm	15.03 mm	20.04 mm	40.09 mm
780 nm	15.10 mm	20.14 mm	40.29 mm
850 nm	15.13 mm	20.17 mm	40.35 mm
1064 nm	15.18 mm	20.24 mm	40.50 mm
1310 nm	15.22 mm	20.30 mm	40.62 mm
1550 nm	15.26 mm	20.36 mm	40.73 mm
3000 nm	15.54 mm	20.74 mm	41.52 mm
4000 nm	15.84 mm	21.15 mm	42.34 mm
5000 nm	16.24 mm	21.70 mm	43.46 mm
8000 nm	18.40 mm	24.65 mm	49.50 mm

Ø1" Bi-Convex Lenses

	LB5774	LB5284	LB5247	LB5552	LB5454
248 nm	23.66 mm	46.40 mm	69.56 mm	92.73 mm	185.42 mm
405 nm	24.99 mm	49.15 mm	73.71 mm	98.28 mm	196.55 mm
488 nm	25.23 mm	49.65 mm	74.47 mm	99.29 mm	198.58 mm
532 nm	25.32 mm	49.83 mm	74.74 mm	99.65 mm	199.30 mm
588 nm	25.40 mm	50.00 mm	75.00 mm	100.00 mm	200.00 mm
633 nm	25.45 mm	50.11 mm	75.17 mm	100.22 mm	200.45 mm
780 nm	25.57 mm	50.35 mm	75.54 mm	100.72 mm	201.44 mm
850 nm	25.61 mm	50.44 mm	75.66 mm	100.88 mm	201.77 mm
1064 nm	25.70 mm	50.62 mm	75.93 mm	101.25 mm	202.50 mm
1310 nm	25.77 mm	50.77 mm	76.17 mm	101.56 mm	203.13 mm
1550 nm	25.84 mm	50.90 mm	76.37 mm	101.83 mm	203.67 mm
3000 nm	26.31 mm	51.89 mm	77.85 mm	103.81 mm	207.64 mm
4000 nm	26.81 mm	52.91 mm	79.40 mm	105.88 mm	211.80 mm
5000 nm	27.48 mm	54.31 mm	81.51 mm	108.70 mm	217.46 mm
8000 nm	31.10 mm	61.82 mm	92.87 mm	123.89 mm	247.94 mm