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CaF2 Calcium Fluoride Technical Data

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Summary Description

CaF2 is a low index (1.40 @ 4 microns) material which is used in a wide variety of commercial applications. In spectroscopy it is a substitute for SiO2 materials, fused quartz, fused silica, BK-7, Suprasil®, Infrasil®, etc. In near-IR applications it is superior to these materials because it has no OH absorption to limit the accuracy of quantitative results. Since it is easy to polish to tight specifications it is the material of choice for near-IR beamsplitters and windows.

Advantages

  1. No infrared impurity absorption bands
  2. Near zero solubility in water
  3. No OH absorption
  4. Can be polished to extremely tight specifications
  5. Low index of refraction
  6. Relatively low cost as compared to SiO2

Disadvantages

  1. Limited spectral coverage in the mid-IR
  2. Slightly sensitive to thermal shock

Physical Data

Melting Point: 1360 °C
Density: 3.18 g/cm3
Solubility in H2O: 0.05 g/100 g at 20 °C
Hardness: 158.3 kg/mm2
Appearance: Crystalline clear

Mid-IR Transmission – 3 mm thick CaF2 window

caf2

Refractive Index1

WAVELENGTH (Microns) INDEX
0.48615 1.43704
0.58758 1.43388
0.58932 1.43384
0.6563 1.43249
0.68671 1.432
0.72818 1.43143
0.76653 1.4276
0.884 1.4298
1.014 1.42884
1.08304 1.42843
1.1 1.42834
1.1786 0.42789
1.25 0.42752
1.3756 1.42689
1.4733 0.42642
1.5715 1.42596
1.65 0.42558
1.768 1.42502
1.84 1.42468
1.8688 0.42454
1.9 1.42439
1.9153 1.42431
1.9644 1.42407
2.0582 1.4236
2.0626 1.42357
2.1608 0.42306
2.25 1.42258
2.3573 1.42198
2.45 0.42143
WAVELENGTH (Microns) INDEX
2.5537 1.4208
2.6519 0.42018
2.7 1.41988
2.75 0.41956
2.800 0.41923
2.88 1.4189
2.9466 0.41823
3.05 1.4175
3.098 0.41714
3.2413 1.4161
3.4 1.41487
3.5359 1.41376
3.8306 1.41119
4.0 1.40963
4.1252 1.40847
4.25 1.40722
4.4 1.40568
4.6 1.40357
4.7146 1.40233
4.8 1.4013
5.0 1.39908
5.3036 1.39522
5.8932 1.38712
6.4825 1.37824
7.0718 1.36805
7.6612 1.35675
8.2505 1.3444
8.8398 1.33075
9.4291 1.31605

Specific index listed; Generic: 1.40 @ 5 microns

Spectral Range

Short Wavelength Limit: 79,500 cm-1 (1 mm)
Long Wavelength Limit: 896 cm-1 (2 mm), 1025 cm-1 (4 mm)

Coatings

Broad band (visible to 8 microns) beamsplitters for FT near-IR spectrometers are in routine production. Narrow band anti-reflective (AR) coatings for laser applications can also be done. CaF2 is often used as a substrate for interference filters.

Typical Uses

  • High resolution large size UV Optics
  • High resolution visible optics, particularly video cameras
  • Near-IR optics and beamsplitter substrates for spectroscopy
  • Mid-IR sampling optics usually aqueous samples

Notes

Short and Long Wavelength Ranges defined for which transmissivity is greater than 50% of stated crystal thickness.

  1. W. Kaiser, W.G. Spitzer, R.H. Kaiser & L.E. Howarth; Physical Review. Vol. 127, p. 1950, 1962

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