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Optical Glass and IR Material Refractive Index Reference Table

This is a quick lookup of refractive index, Abbe number, transmission window and typical use for the optical glasses, crystals, semiconductors and polymers that photonics shops buy and cut most often. Use the search box to filter by material, wavelength or application, then export to Excel or CSV for your engineering notes.

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MaterialFamilyRefractive index (approx.)At wavelengthAbbe number (Vd)Useful transmission windowTypical use
N-BK7 (borosilicate crown)
Optical glass
1.5168
587.6 nm (d line)
64.2
0.35 to 2.0 um
General lenses, windows, prisms, laser optics in visible and NIR
UV fused silica
Synthetic glass
1.4585
587.6 nm
67.8
0.18 to 2.1 um
UV and high-power laser optics, low thermal expansion substrates
N-F2 (flint)
Optical glass
1.6200
587.6 nm
36.4
0.37 to 2.5 um
Flint element in achromatic doublets
N-SF6 (dense flint)
Optical glass
1.8052
587.6 nm
25.4
0.38 to 2.5 um
High-index flint, compact lens designs
N-SF11 (dense flint)
Optical glass
1.7847
587.6 nm
25.7
0.37 to 2.5 um
High-index prisms and achromat flint elements
N-LASF9 (lanthanum dense flint)
Optical glass
1.8503
587.6 nm
32.2
0.37 to 2.5 um
High-index, high-power lens designs
Borosilicate 33 (float glass)
Technical glass
1.472
587.6 nm
65
0.33 to 2.5 um
Cover glass, sensor windows, low-cost substrates
Calcium fluoride (CaF2)
Crystal
1.4338
587.6 nm
95.0
0.13 to 10 um
UV to mid-IR windows, excimer laser optics, apochromats
Barium fluoride (BaF2)
Crystal
1.4744
587.6 nm
81.7
0.15 to 12 um
Broad UV to LWIR windows, scintillator and spectroscopy
Magnesium fluoride (MgF2)
Crystal
1.378
587.6 nm (ordinary ray)
106
0.13 to 7 um
VUV windows and low-index AR coating material
Sapphire (Al2O3)
Crystal
1.768
587.6 nm (ordinary ray)
72
0.17 to 5.5 um
Hard, scratch-resistant windows, high-pressure and harsh environments
Zinc selenide (ZnSe)
IR crystal
2.403
10.6 um
n/a
0.6 to 16 um
CO2 laser lenses and windows, FLIR optics
Zinc sulfide (multispectral ZnS)
IR crystal
2.20
10 um
n/a
0.4 to 12 um
Dual-band domes and windows, visible plus thermal imaging
Germanium (Ge)
IR semiconductor
4.00
10.6 um
n/a
2 to 14 um
Thermal imaging lenses, LWIR windows, opaque in the visible
Silicon (Si)
IR semiconductor
3.42
3 to 5 um
n/a
1.2 to 7 um
MWIR windows, laser mirror substrates, opaque in the visible
PMMA (acrylic)
Optical polymer
1.491
587.6 nm
57
0.4 to 1.1 um
Low-cost molded lenses and light guides
Polycarbonate
Optical polymer
1.586
587.6 nm
30
0.4 to 1.1 um
Impact-resistant lenses, safety covers, eyewear lenses

Values are rounded catalogue figures at the stated wavelength and vary slightly by melt, grade and temperature. Always take final values from the glass or crystal supplier datasheet or melt report for design and acceptance.

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How to use the table

Type a material name, a family such as crystal, or a wavelength into the search box. The index column is quoted at the wavelength shown beside it, so do not compare a visible-light index with an infrared one. For design work, take the index at your actual operating wavelength from the supplier dispersion formula, because index changes with wavelength, temperature and sometimes crystal orientation.

  • Match the index wavelength to your laser or detector band
  • Check the transmission window before shortlisting a material
  • Use Abbe number to pick crown and flint pairs for achromats
  • Export the filtered rows for a bill of materials review

What the numbers mean

Refractive index n sets how strongly light bends and how much Fresnel reflection occurs at each uncoated surface. At normal incidence the reflection per surface is ((n-1)/(n+1)) squared, which is about 4 percent for BK7 and over 30 percent for germanium in the LWIR. That is why high-index infrared optics always need antireflection coatings. The Abbe number measures dispersion: high values (above about 55) mean low colour spread, low values mean strong dispersion.

Choosing a substrate for a laser or detector band

Start from the wavelength. Visible and near infrared work comfortably in BK7 or fused silica. Deep UV and excimer lines need fused silica or CaF2. CO2 laser work at 10.6 um needs ZnSe, germanium or similar infrared materials, since glass absorbs there. Then check hardness, thermal expansion, absorption and cost. Sapphire is hard but expensive to polish, ZnSe is soft and toxic when machined dry, and germanium loses transmission as temperature rises.

  • UV: fused silica, CaF2, MgF2
  • Visible and NIR: N-BK7, fused silica, flint glasses
  • MWIR: silicon, sapphire, ZnS
  • LWIR and CO2 lasers: ZnSe, germanium, ZnS

Common mistakes

The most common error is using the sodium d-line index for a laser at 1064 nm or 10.6 um, which can shift focal length noticeably. The second is ignoring birefringence in sapphire and MgF2, where the ordinary and extraordinary rays differ. The third is accepting a substitute glass by index alone without checking Abbe number, transmission and bubble class. In ERP, record the exact glass code and supplier melt on the item so receiving inspection can verify it.

Frequently Asked Questions

What is the refractive index of N-BK7?

N-BK7 has a refractive index of about 1.5168 at the 587.6 nm sodium d line and an Abbe number near 64. Its index falls slowly toward the infrared, around 1.507 at 1064 nm. Use the supplier Sellmeier coefficients for exact values at your wavelength.

Why does infrared optics use germanium and ZnSe instead of glass?

Ordinary optical glasses absorb strongly beyond roughly 2.5 um, so they are opaque to CO2 laser light at 10.6 um and to thermal imaging bands. Germanium, ZnSe and ZnS transmit in the long-wave infrared, though they are expensive and need antireflection coatings because of their high index.

What is the difference between refractive index and Abbe number?

Refractive index tells you how much a material bends light at one wavelength. The Abbe number summarises how much that index changes across the visible spectrum. Low Abbe means high dispersion and more colour error, so achromats pair a high-Abbe crown with a low-Abbe flint to cancel it.

Can I use these values for final lens design?

Use them for screening and quick checks only. Final design needs the supplier dispersion formula and melt data, because index varies by melt, annealing and temperature. Many optical glass suppliers publish melt-specific index certificates that you should capture at receiving.

If your optical item masters, melt certificates and incoming inspection results live in an ERP, we can build a private assistant that answers material and substitution questions from your own data. We can show you how that works on your system.

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