Infrared Optical Materials
Compare IR transmitting materials and glasses. n(λ, T) = n(λ, T₀) + (dn/dT)(T − T₀), with n(λ, T₀) from each material's published Sellmeier formula.
n at 4 µm, 25 °C
4.0259
J. H. Burnett et al., Proc. SPIE 9974, 99740X (2016); dn/dT from 22 °C
Fresnel-limited transmission
46.8 %
2n/(n² + 1), uncoated, both surfaces, no absorption
Transmission band
1.8–23 µm
dn/dT
+396 ×10⁻⁶/K
Thermal conductivity
58.62 W/(m·K)
Knoop hardness
780 kg/mm²
Refractive Index vs Wavelength
Transmission Bands
Model
n(λ, T) = n(λ, T₀) + (dn/dT)(T − T₀), T_max = 2n/(n² + 1)
n(λ, T₀) comes from each material's published Sellmeier formula at the temperature T₀ of its measurements, within the formula's wavelength range (the same data sets as the Material Dispersion calculator; the ordinary index for MgF₂). dn/dT is one room-temperature value per material, so treat n(T) far from T₀ as an estimate. T_max is the transmission of an uncoated, non-absorbing window with both surfaces' multiple reflections added in intensity: an upper bound that absorption near the band edges lowers. Bands, dn/dT, conductivity and Knoop hardness are Crystran data-sheet values, and Amorphous Materials' for AMTIR-1 and As₂S₃. ZBLAN's Knoop hardness and dn/dT are from Poulain's 2024 review: dn/dT is the midpoint of the −8 to −15 ×10⁻⁶/K reported for fluoride glasses, so its n(T) is good to about ±3.5 ×10⁻⁶ per kelvin. ZBLAN has no sourced band or conductivity.
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
Index from published Sellmeier fits inside their ranges, shifted linearly by one room-temperature dn/dT; transmission is the lossless two-surface Fresnel limit 2n/(n² + 1). Bands, dn/dT, conductivity and hardness are Crystran data-sheet values, and Amorphous Materials' for AMTIR-1 and As₂S₃ (AMTIR-6: band and hardness only, its dn/dT changes sign across the band); ZBLAN's Knoop 250 kg/mm² and dn/dT −11.5 ×10⁻⁶/K (midpoint of −8 to −15 for fluoride glasses) are from Poulain's 2024 review, with no band or conductivity. AMTIR-1's single dn/dT is about 2× low below 1.5 µm.
- refractiveindex.info database (CC0). Sellmeier data sets, each with its original reference shown on the page. Used for Ge, Si, ZnSe, ZnS, CaF₂, BaF₂, MgF₂, NaCl, KBr, CsI, KRS-5, As₂S₃ and ZBLAN.
- Rodney W. S., Malitson I. H. (1956). Refraction and dispersion of thallium bromide iodide. J. Opt. Soc. Am. 46, 956. KRS-5 Sellmeier formula at 25 °C (0.577–39.38 µm) and dn/dT. doi:10.1364/JOSA.46.000956
- Rodney W. S., Malitson I. H., King T. A. (1958). Refractive index of arsenic trisulfide. J. Opt. Soc. Am. 48, 633. doi:10.1364/JOSA.48.000633
- Gan F. (1995). Optical properties of fluoride glasses: a review. J. Non-Cryst. Solids 184, 9. ZBLAN dispersion formula (n_d 1.5011). doi:10.1016/0022-3093(94)00592-3
- Zhu X., Peyghambarian N. (2010). High-power ZBLAN glass fiber lasers: review and prospect. Adv. OptoElectron. 2010, 501956. Table 1: ZBLAN n 1.499 at 589 nm, Abbe number 76; n_d varies with composition by a few 10⁻³. doi:10.1155/2010/501956
- Poulain M. (2024). Heavy metal fluoride glasses: A tutorial review. APL Photonics 9, 091103. Knoop hardness about 250 kg/mm² for ZBLAN (Table IV: fluorozirconates 190–250) and dn/dT −8 to −15 ×10⁻⁶/K for fluoride glasses. doi:10.1063/5.0226668
- Li H. H. (1976). Refractive index of alkali halides and its wavelength and temperature derivatives. J. Phys. Chem. Ref. Data 5, 329. doi:10.1063/1.555536
- Crystran. Handbook of Infrared and Ultraviolet Optical Materials, data sheets: transmission range, dn/dT, thermal conductivity, Knoop hardness. crystran.com
- Amorphous Materials Inc. (2024). AMTIR-1 data sheet: Sellmeier fit at 22 °C, index and dn/dT table 1–14 µm at 20 °C (2.49701 and 71 ×10⁻⁶/K at 10 µm), thermal conductivity 0.25 W/(m·K), Knoop hardness 170. web.archive.org
- Amorphous Materials Inc. Comparison of IR transmitting glasses produced by AMI, ver. 5: transmission ranges AMTIR-1 0.7–12 µm, AMTIR-6 (As₂S₃) 0.6–8 µm; Knoop 170 and 109. web.archive.org
- Amorphous Materials Inc. (2020). AMTIR-6 data sheet: As₂S₃ index 2.4994, 2.4202, 2.4070, 2.3976 and dn/dT 20.7, 4.19, −2.65, −3.54 ×10⁻⁶/K at 0.9, 3, 6, 8 µm (22 °C). web.archive.org
- Born M., Wolf E. (1999). Principles of Optics, 7th ed. Cambridge University Press. Fresnel formulae at normal incidence.