Common infrared optical material coating、characteristics、performance and application


Barium Fluoride (BaF2)
• Good transmission within the UV, VIS, NIR, and MW spectral regions
• Hardness about half that of CaF2
• Is about 70% the mechanical strength of CaF2
• More vulnerable to thermal shock than CaF2
• Somewhat costlier than CaF2
• Not as readily available in large sizes as CaF2
• Diamond turnable
• Magnetorheological finishable
Transmission range
Transmission is above 90 percent between 0.25 and 9.5 μm
Index of refraction
1.466 @ 1.7 μm
1.455 @ 4 μm
dn/dT
−15.2 × 10−6/K
Density: 4.89 g/cm3
Hardness (Knoop): 82 kg/mm2
Rupture modulus
3800 psi
Thermal expansion coefficient
18.1 × 10−6/°C @ 20 °C ±100 °C 
Typical applications
Thermal imaging, astronomy, lasers
Products manufactured
Lenses, aspheric lenses, windows, beamsplitters, optical filters, wedges, and prisms 
Surface finish
Polishes of 20-10 scratch-dig are mostly specified for UV and VIS applications. Typical specifications for surface quality within the IR are a 40-20 scratch-dig within the NIR spectral region and 60-40 scratch-dig for the MW area.
Surface figure
The surface figure of 1/10 to 1/4 wave @ 0.6328 μm are specified totally on lenses for UV and VIS use. In the IR, the typical surface figure ranges from 1/2 to 2 waves @ 0.6328 μm. 
AR coating options
Typically available coatings for BaF2 include BBAR for 0.8 μm to 2.5 μm, 3 μm to five μm, or 1 μm to five μm, and dual-band AR for the three .5- to 5.1-μm and seven .5- to 10.5-μm spectral regions. 

Cadmium Telluride (CdTe)
• Extra handling and safety precautions are required when machining this material thanks to its toxicity; thus, few companies will process it 
• Has the very best density of the common infrared-transmitting materials 
• one among the widest transmission ranges of any infrared material 
• Principally utilized in the 12- to 25-μm spectral region, where many other infrared materials have absorption bands 
• Slightly but half the hardness of ZnSe 
• Significantly costlier than Ge and ZnSe 
• Diamond turnable 
Transmission range
1 to 25 μm 
Index of refraction
2.693 @ 4 μm 
2.676 @ 10 μm 
2.640 @ 19 μm 
dn/dT
5.0 × 10−5/K 
Density
5.85 g/cm3
Hardness (Knoop) 
45 kg/mm2
Rupture modulus 
3191 psi 
Thermal expansion coefficient
5.9 × 10−6/°C @ 20 °C 
Typical applications
Thermal imaging, low-power CO2 laser systems, detectors 
Products manufactured
Lenses, aspheric lenses, windows, detector windows, beamsplitters, optical filters, wedges and prisms 
Surface finish
Typical specifications for surface quality within the IR are a 40-20 scratch-dig within the NIR spectral region and 60-40 scratch-dig for the MW spectral region, and 60-40, 80-50 or 120-80 scratch-dig above 7 μm. 
Surface figure 
Ranges from 1/2 to 2 waves @ 0.6328 μm 
AR coating options
CdTe are often AR-coated for various wavelengths or wavelength ranges between 1 and 25 μm. 

Calcium Fluoride (CaF2) 
• Good transmission within the UV, VIS, NIR, and MW spectral regions 
• it's a transmission above 90 percent between 0.25 and seven μm 
• Is about twice as hard as BaF2
• Less vulnerable to thermal shock than BaF2
• doesn't degrade thanks to moisture under ambient atmospheric conditions 
• less costly than BaF2
• More readily available than BaF2 in large sizes 
• Diamond turnable 
• Magnetorheological finishable 
Transmission range
0.13 to 10 μm 
Index of refraction
1.428 @ 1.064 μm 
1.425 @ 1.7 μm 
1.4096 @ 4 μm 
dn/dT
−11.0 × 10−6/K 
Density
3.18 g/cm3
Hardness (Knoop)
158 kg/mm2
Rupture modulus
5295 psi 
Thermal expansion coefficient
18.85 × 10−6/°C 
Typical applications
Imaging, thermal imaging, astronomy, microlithography, laser 
Products manufactured 
Lenses, aspheric lenses, windows, beamsplitters, optical filters, wedges, and prisms 
Surface finish
Polishes of 20-10 scratch-dig are mostly specified to be used in UV and VIS applications. Typical specifications within the infrared are 40-20 scratch-dig for the NIR spectral region and 60-40 scratch-dig for the MW spectral region. 
Surface figure
In the UV and VIS spectral regions, the specified surface figure ranges from 1/10 to 1/4 wave @ 0.6328 μm. In the IR, the typically required surface figure ranges from 1/4 to 2 waves @ 0.6328 μm. 
AR coating options
Available coatings include BBAR for the 0.8 to 2.5, 3 to 5, or 1 to five μm, dual-band AR for MWIR and LWIR, and triple-band for NIR and MWIR spectral regions. Other options also are available. 

Cesium Bromide (CsBr) 
• Optical-grade cesium bromide transmits from the UV to the far-IR; one among the widest transmission bands of the IR materials. 
• it's water-soluble, requiring protection from water moisture and humidity: accomplished by using moisture-protection AR coatings or by ensuring uncoated part is during a water-/humidity-free environment. 
• Diamond turnable 
• Extremely fragile 
Transmission range
Transmission is above 80 percent from 0.35 to 32 μm. 
Index of refraction 
1.668 @ 4 μm 
1.663 @ 10 μm 
1.629 @ 25 μm 
dn/dT
+79 × 10−6/°C 
Density
4.44 g/cm3
Hardness (Knoop)
19.5 kg/mm2
Rupture modulus
1218 psi 
Thermal expansion coefficient
47.9 × 10−6/°C 
Typical applications
FTIR spectroscopy, laser systems, lens protectors for CO2 laser systems, imaging systems, analytical instruments 
Products manufactured
Windows, lenses, laser lens protectors, aspheric lenses, wedges and prisms 
Surface finish
Typical specifications for surface quality within the IR are 60-40, 80-50 or 120-80 scratch-dig. 
Surface figure
In the IR, the standard surface figure specified ranges from 1/10 to 1/40 wave @ 10.6 μm. 
AR coating options
Moisture-protection AR and BBAR coatings are available for various wavelengths or wavelength ranges within CsBr’s transmission range. 

Cesium Iodide (CsI)
• Optical-grade cesium iodide transmits from the UV to the far-infrared; it's the widest transmission band of all the readily available IR materials. 
• it's water-soluble, requiring protection from water moisture and humidity: accomplished by using moisture-protection AR coatings or by ensuring uncoated part is during a water-/humidity-free environment. 
• Diamond turnable 
• Extremely fragile 
Transmission range
Transmission is above 80 percent from 0.42 to 40 μm. 
Index of refraction
1.743 @ 4 μm 
1.739 @ 10 μm 
1.708 @ 30 μm 
dn/dT
−99 × 10−6/°C @ 0.6 μm 
Density
4.51 g/cm3
Hardness (Knoop)
20 kg/mm2
Rupture modulus 
809 psi 
Thermal expansion coefficient
50 × 10−6/°C 
Typical applications
FTIR spectroscopy, laser systems, lens protectors for CO2 laser systems, imaging systems, analytical instruments 
Products manufactured
Windows, lenses, laser lens protector windows, aspheric lenses, prisms, and wedges 
Surface finish
Typical specifications for surface quality within the IR are 60-40, 80-50, or 120-80 scratch-dig. 
Surface figure
In the IR, the standard surface figure specified ranges from 1/10 to 1/40 wave @ 10.6 μm. 
AR coating options
Moisture-protection AR and BBAR coatings are available for various wavelengths or wavelength ranges within CSI's transmission range.

Fused Silica (SiO2), IR Grade

• IR-grade fused silica is employed in NIR systems, usually alongside other materials like CaF2.
• it's high homogeneity and good transmission within the VIS and NIR spectral regions.
• thanks to the material’s inherently hard SiO2 amorphous structure, fused silica isn't diamond turnable, making it far more difficult and dear to fabricate finished aspheric surfaces.
Transmission range
0.25 to 3.5 μm
Index of refraction
1.4505 @ 1 μm 
1. 4382 @ 2 μm
dn/dT

Density
2.203 g/cm3
Hardness (Knoop)
461 kg/mm2
Rupture modulus
7100 psi 
Thermal expansion coefficient
0.58 × 10−6/°C @ 0 to 200 °C 
Typical applications
Visible and thermal imaging, astronomy, laser 
Products manufactured
Lenses, windows, wedges, beamsplitters, optical filters, and prisms 
Surface finish
Typical specifications for surface quality within the NIR regions are 40-20 scratch-dig. 
Surface figure
In the VIS and NIR, the typical surface figure ranges from 1/10 to 1 wave @ 0.6328 μm. 
AR coating options
Typical available NIR coatings are BBAR for 0.8 to 2.5 μm and AR for 1.064 μm. Other coatings for UV, VIS, and NIR applications also are available.

Gallium Arsenide (GaAs)
• Optical-grade gallium arsenide is IR-transmitting and semi-insulating. 
• Nearly equivalent in hardness, strength, and density to Ge
• Commonly utilized in applications where toughness and sturdiness are of great importance 
• Low coefficient of absorption of 0.01 cm−1 from 2.5 to 12 μm
• Generally costlier than Ge and ZnSe
• Diamond turnable 
Transmission range
2 to fifteen μm 
Index of refraction
3.307 @ 4 μm 
3.278 @ 10 μm 
3.251 @ 14 μm
dn/dT
148 × 10−6/K
Density
5.31 g/cm3
Hardness (Knoop)
750 kg/mm2
Rupture modulus
10,436 psi 
Thermal expansion coefficient
6 × 10−6/K 
Typical applications
Thermal imaging, CO2 laser systems, FLIR 
Products manufactured
Lenses, aspheric lenses, windows, wedges, and prisms 
Surface finish
Typical specifications for surface quality within the IR are 40-20 or 60-40 scratch-dig within the 2- to 7-μm region and 60-40, 80-50 or 120-80 scratch-dig for 7 to fifteen μm. 
Surface figure
In the IR, the typical surface figure ranges from 1/2 to 2 waves @ 0.6328 μm. 
AR coating options
Typically available coatings include BBAR within the 3- to 5-μm and 8- to 12-μm regions. Other specialized bands also are possible within the 2- to 15-μm region.

Germanium (Ge)
• Germanium has the very best index of refraction of any commonly used IR-transmitting material. 
• it's very fashionable for systems operating within the 3- to 5-μm or 8- to 12-μm spectral regions.
• Its high index of refraction makes it desirable for the planning of lenses that otherwise won't be possible.
• Germanium may be a diamond-turnable material, so it's possible to include aspheric and diffractive surfaces cost-effectively, which may successively reduce the number of lens elements required in an assembly. 
• Germanium naturally blocks UV and VIS light, also as IR up to about 2 μm. 
• Germanium features a large thermo-optic coefficient (dn/dT), causing large focus shifts with temperature which will make a thermalization of an optical system difficult.
• Germanium has nearly the very best density of the IR-transmitting materials, which must be taken under consideration when designing weight-restricted systems. 
• the fabric is additionally vulnerable to thermal runaway; the warmer it gets, the more its absorption increases. 
• Pronounced transmission degradation starts at about 100 °C, and rapid degradation begins between 200 and 300 °C, leading to possible catastrophic failure of the optic.
• Germanium is usually less costly than ZnSe and Cleartran.
• Diamond turnable
• Magnetorheological finishable
Transmission range
2 to 14 μm up to about 45 °C 
Index of refraction
4.025 @ 4 μm 
4.003 @ 10 μm
dn/dT
396 × 10−6/K
Density
5.323 g/cm3
Hardness (Knoop)
780 kg/mm2
Rupture modulus
10,500 psi 
Thermal expansion coefficient
2.3 × 10−6/K @ 100 K 
5.0 × 10−6/K @ 200 K 
6.0 × 10−6/K @ 300 K
Typical applications
Thermal imaging, FLIR, FTIR, analytical instruments 
Products manufactured
Lenses, aspheric lenses, binary (diffractive) lenses, windows, beamsplitters, optical filters, wedges, and prisms 
Surface finish
Typical specifications for surface quality within the IR are 40-20 or 60-40 scratch-dig within the 2- to the 7-μm spectral region and 60-40, 80-50 or 120-80 scratch-dig for 7 to 14 μm. Diamond-turned surface finishes of fifty Å rms or better are typical. 
Surface figure
In the IR, the standard specified surface figure ranges from 1/4 to 2 waves @ 0.6328 μm. 
AR coating options
Typically available coatings include BBAR for the 3- to 5-μm, 8- to 14-μm, and 3- to 14-μm spectral regions. Other application-specialized bands also are possible between 2 and 14 μm. Ge also can be diamondlike carbon-coated within the 3- to 5-μm or 8- to 12-μm regions. 

Lithium Fluoride (LiF)
• Lithium fluoride has a rock bottom index of refraction of all the common IR materials. 
• it's slightly plastic, meaning that when it's mechanically stressed, it doesn’t come to its original form.
• It also features a relatively high thermal expansion coefficient and is that the costliest of the fluoride series of crystals. 
• Diamond turnable
• Magnetorheological finishable 
Transmission range
0.12 to 8.5 μm 
Index of refraction
1.373 @ 2.5 μm 
1.349 @ 4.0 μm
dn/dT
−12.7 × 10−6/°C @ 0.6 μm
Density
2.639 g/cm3
Hardness (Knoop) 
102 kg/mm2
Rupture modulus 
1566 psi 
Thermal expansion coefficient
37 × 10−6/°C
Typical applications
Visible and thermal imaging, astronomy, laser 
Products manufactured
Lenses, aspheric lenses, windows, wedges, prisms 
Surface finish
Typical specifications for surface quality within the IR are 40-20 scratch-dig within the NIR and 60-40 or 80-50 scratch-dig for the MW area.
Surface figure
In the IR, the typically required surface figure ranges from 1/2 to 2 waves @ 0.6328 μm. 
AR coating options
LiF is often AR-coated to be used within the IR, but often without much improvement in transmission thanks to its low index of refraction and already high transmission.

Magnesium Fluoride (MgF2)
• Magnesium fluoride is one among the lowest-index IR materials, second only to LiF. 
• Its birefringence should be taken into consideration before the selection of this material in an optical design. 
• it's immune to thermal and mechanical shock. 
• it's twice as hard as CaF2 but only half as hard as Ge. 
• it's significantly costlier than CaF2 and BaF2, but usually less expensive than LiF. 
• Diamond turnable 
• Magnetorheological finishable 
Transmission range
0.11 to 7.5 μm 
Index of refraction
1.376 @ 0.7 μm 
1.370 @ 1.7 μm 
1.349 @ 4.0 μm 
dn/dT
+2.3 & +1.7 × 10−6/°C @ 0.4 μm 
Density
3.18 g/cm3
Hardness (Knoop)
415 kg/mm2
Rupture modulus 
7108 psi 
Thermal expansion coefficient 
13.7 × 10−6/°C parallel to C-axis 
8.48 × 10−6/°C perpendicular to C-axis 
Typical applications
Visible and thermal imaging, astronomy, excimer laser 
Products manufactured
Lenses, aspheric lenses, windows, beamsplitters, optical filters, wedges, and prisms 
Surface finish
Polishes of 10-5 or 20-10 scratch-dig are achieved at extra costs mainly for UV applications. Typical specifications for surface quality within the VIS and NIR regions are 40-20 and 60-40 scratch-dig within the MW range. 
Surface figure
In the UV and VIS, the surface figure ranges from 1/10 to 1/2 wave @ 0.6328 μm. In the IR, the typically required surface figure ranges from 1/2 to 2 waves @ 0.6328 μm. 
AR coating options
MgF2 are often AR-coated to be used within the IR but often without much improvement in transmission thanks to its low index of refraction and already high transmission.


Potassium Bromide (KBr)
• Transmits from the UV to the far-IR 
• Is water-soluble, requiring protection from water moisture and humidity: accomplished by using moisture-protection AR coatings or by ensuring the uncoated part is during a water-/humidity-free environment. 
• one among the widest transmission bands of the IR materials 
• doesn't have as great durability as KCl or NaCl 
• Generally costlier than KCl and quite bit quite NaCl 
• Diamond turnable 
• Extremely fragile 
Transmission range
Transmission is above 80 percent from 0.26 to 23 μm 
Index of refraction
1.535 @ 4 μm 
1.525 @ 10 μm 
1.490 @ 20 μm 
dn/dT 
−40.83 × 10−6/°C 
Density
2.754 g/cm3
Hardness (Knoop)
5.9 kg/mm2
Rupture modulus
159 psi 
Thermal expansion coefficient
43 × 10−6/°C 
Typical applications
FTIR spectroscopy, laser systems, lens protectors for CO2 laser systems, imaging systems, analytical instruments 
Products manufactured
Windows, lenses, laser lens protector windows, aspheric lenses, windows, wedges and prisms 
Surface finish
Typical specifications for surface quality within the IR are 60-40, 80-50 or 120-80 scratch-dig. 
Surface figure
In the IR, the standard surface figure specified ranges from 1/10 to 1/40 wave @ 10.6 μm. 
AR coating options
Moisture-protection AR and BBAR coatings are available for various wavelengths or wavelength ranges within KBr’s transmission range. 

Potassium Chloride (KCl)
• Transmits from the UV to the far-IR; one among the widest transmission bands of the IR materials. 
• Is water-soluble, requiring protection from water moisture and humidity: accomplished by using moisture-protection AR coatings or by ensuring the uncoated part is during a water-/humidity-free environment. 
• Higher rupture modulus than KBr, but not NaCl 
• Generally less costly than KBr and costlier than NaCl 
• Diamond turnable 
• Extremely fragile 
Transmission range
Transmission is above 80 percent from 0.3 to 21 μm 
Index of refraction
1.472 @ 4 μm 
1.456 @ 10 μm 
1.426 @ 16 μm 
dn/dT
−33.2 × 10−6/°C 
Density
1.989 g/cm3
Hardness (Knoop)
7.2 kg/mm2
Rupture modulus
330 psi 
Thermal expansion coefficient
36 × 10−6/°C 
Typical applications
FTIR spectroscopy, laser systems, lens protectors for CO2 laser systems, imaging systems, analytical instruments 
Products manufactured
Windows, lenses, laser lens protector windows, aspheric lenses, wedges and prisms 
Surface finish
Typical specifications for surface quality within the IR region are 60-40, 80-50, or 120-80 scratch-dig. 
Surface figure
In the IR, the standard surface figure specified ranges from 1/10 to 1/40 wave @ 10.6 μm. 
AR coating options
Moisture-protection AR and BBAR coatings are available for various wavelengths or wavelength ranges within KCl’s transmission range. 

Sapphire (Al2O3)
• Sapphire is one among the toughest and most durable optical materials. 
• Transmits from about 0.25 to five μm 
• Commonly utilized in IR optical systems, operating within the NIR and MW spectral bands. 
• Sapphire’s crystal structure features a rhombohedral shape and is very anisotropic, meaning its optical and mechanical properties vary with the crystal’s orientation. 
• Withstands harsh environmental conditions 
• it's harder than most all-optical materials, with the exception of a diamond. 
• Low dn/dT 
• Sapphire isn't diamond turnable, thus making it harder and dear to get and polish aspheric surfaces into it. 
• Magnetorheological finishable 
Transmission range
0.17 to 5.5 μm 
Index of Refraction
no = 1.768 
ne = 1.760 
dn/dT
+13 × 10−6/K 
Density
3.98 g/cm3
Hardness (Knoop)
2200 kg/mm2 perpendicular to the C-axis 
1900 kg/mm2 parallel to the C-axis 
Rupture modulus 
52 × 106 psi (358 GPa) 
Thermal expansion coefficient 
8.4 × 10−6/°C 
Typical applications 
High mechanical shock and vibration, thermal imaging, FLIR 
Products manufactured 
Lenses, aspheric lenses, domes, windows, beamsplitters, optical filters, wedges, and prisms 
Surface finish 
Typical specifications for surface quality within the IR are 40-20 scratch-dig within the 1.2- to 3-μm region and 60-40 for 3 to 7 μm. 
Surface figure 
In the IR, the typically required surface figure ranges from 1/4 to 2 waves @ 0.6328 μm. 
AR coating options 
AR coatings for sapphire include BBAR for 3 to five μm. Many other specialized wavelength bands are possible within the 0.25- to the 5.0-μm range. 

Silicon (Si), Transmitting Grade 
• Silicon may be a semiconductor material commonly utilized in IR optical systems operating within the NIR and MW spectral bands. 
• With one among rock bottom densities of the common IR materials, it's ideal for systems with weight constraints. 
• Harder than Ge and not as brittle 
• is that the lowest material cost option of all the IR materials but is costlier to process than many of the opposite IR materials thanks to its hardness. 
• Diamond turnable 
• Magnetorheological finishable 
Transmission range 
1.2 to 7.0 μm (also from 25 bent beyond 300 μm) 
Index of refraction 
3.4289 @ 4 μm 
dn/dT 
+160 × 10−6/K 
Density 
2.329 g/cm3 
Hardness (Knoop) 
1150 kg/mm2 
Rupture modulus 
18,000 psi 
Thermal expansion coefficient 
2.55 × 10−6/°C @ 25 °C 
Typical applications 
Thermal imaging, FLIR 
Products manufactured 
Lenses, aspheric lenses, binary (diffractive) lenses, windows, beamsplitters, optical filters, wedges, and prisms 
Surface finish 
Typical specifications for surface quality within the IR are 40-20 scratch-dig within the 1.2- to 3-μm region and 60-40 for 3 to 7 μm. Diamond-turned surface finishes of fifty Å rms or better are typical. 
Surface figure 
In the IR, the typically required surface figure ranges from 1/4 to 2 waves @ 0.6328 μm. 
AR coating options 
The most common AR coating for Si is BBAR for 3 to five μm. Many other specialized wavelength bands are possible for the 1.2- to the 7.0-μm range. Si also can be hard carbon or diamondlike carbon coated for 3 to five μm. 

Sodium Chloride (NaCl) 
• Optical-grade NaCl is water-soluble and transmits from the UV to the far-IR. 
• Is water-soluble, requiring protection from water moisture and humidity: accomplished by using moisture-protection AR coatings or by ensuring the uncoated part is during a water-/humidity-free environment. 
• More durable than KBr or KCl 
• Diamond turnable 
• Extremely fragile 
Transmission range 
Transmission is above 80 percent from 0.23 to 12 μm 
Index of refraction 
1.522 @ 4 μm 
1.495 @ 10 μm 
dn/dT 
−36 × 10−6/°C @ 0.7 μm 
Density 
2.165 g/cm3 
Hardness (Knoop) 
15.2 kg/mm2 
Rupture modulus 
345 psi 
Thermal expansion coefficient 
44 × 10−6/°C 
Typical applications 
FTIR spectroscopy, laser systems, lens protectors for CO2 laser systems, imaging systems, and analytical instruments 
Products manufactured 
Windows, lenses, laser lens protectors, aspheric lenses, wedges, and prisms 
Surface finish 
Typical specifications of surface quality within the IR are 60-40, 80-50, or 120-80 scratch-dig. 
Surface figure 
In the IR, the standard surface figure specified ranges from 1/10 to 1/40 wave @ 10.6 μm. 
AR coating options 
Moisture-protection AR and BBAR coatings are available for various wavelengths or wavelength ranges within NaCl’s transmission range. 

Thallium Bromoiodide (KRS-5)
• Optical-grade KRS-5 transmits from the visible to the far-IR 
• Does cold flows when subjected to pressure 
• Surface figure is extremely difficult to carry thanks to the properties of the material 
• it's much harder than NaCl, KBr, and KCl and only about one-third as hard as ZnSe 
• KRS-5 is diamond turnable 
• Extra handling and safety precautions are required when machining this material 
Transmission range 
Transmission is above 70 percent @ 0.7 to 32 μm 
Index of refraction 
2.382 @ 4 μm 
2.371 @ 10 μm 
2.318 @ 25 μm 
dn/dT 
−235 × 10−6/°C 
Density 
7.371 g/cm3 
Hardness (Knoop) 
40 kg/mm2 
Rupture modulus 
3772 psi 
Thermal expansion coefficient 
58 × 10−6/°C 
Typical applications 
FTIR spectroscopy, laser systems, imaging systems, and analytical instruments 
Products manufactured 
Windows, lenses, laser lens protectors, aspheric lenses, prisms, and wedges 
Surface finish 
Typical specifications for surface quality within the IR are 60-40, 80-50, or 120-80 scratch-dig. 
Surface figure 
In the IR, the standard surface figure specified ranges from 1/10 to 1/40 wave @ 10.6 μm. 
AR coating options 
AR and BBAR coatings are available for various wavelengths or wavelength ranges within KRS-5’s transmission range. 

Zinc Selenide (ZnSe) 
• As a chemical vapor deposited (CVD) material, ZnSe is that the material of choice for optics utilized in high-power CO2 laser systems thanks to its low absorption at 10.6 μm. 
• ZnSe is additionally a well-liked choice in systems operating at various bands within its wide transmission range. 
• Its high resistance to thermal shock makes it the prime material for high-power CO2 laser systems. 
• ZnSe is merely about two-thirds the hardness of ZnS multispectral grade, but the harder AR coatings serve to guard ZnSe. 
• ZnSe’s cost is about an equivalent as ZnS Clear grade. 
• Generally costlier than Ge 
• Diamond turnable 
Transmission range 
0.6 to 16 μm 
Index of refraction 
2.4332 @ 4.0 μm 
2.4065 @ 10.0 μm 
2.4028 @ 10.6 μm 
dn/dT 
(avg. @ 298 to 358 K) 
107 × 10−6/K @ 1.15 μm 
70 × 10−6/K @ 1.15 μm 
62 × 10−6/K @ 3.39 μm 
61 × 10−6/K @ 10.6 μm 
Density 
5.27 g/cm3 
Hardness (Knoop) 
110 kg/mm2 
Rupture modulus 
7979 psi 
Thermal expansion coefficient 
7.1 × 10−6/K @ 273 K 
7.8 × 10−6/K @ 373 K 
8.3 × 10−6/K @ 473 K 
Typical applications CO2 laser systems, thermal imaging, FLIR, astronomy, medical 
Products manufactured 
Lenses, aspheric lenses, binary (diffractive) lenses, windows, beamsplitters, optical filters, and prisms 
Surface finish 
Typical specifications for surface quality within the IR are 40-20 or 60-40 scratch-dig within the NIR and MW, and 60-40, 80-50, or 120-80 scratch-dig within the LW region. Diamond-turned surface finishes of 100 Å RMS or better are typical. 
Surface figure 
In the NIR and IR, typically required surface figures range from 1/4 to 2 waves @ 0.6328 μm. 
AR coating options 
Typically available coatings include DLC for MWIR and LWIR, BBAR for the 0.8- to 2.5-, 3- to 5, 1- to 5-, 8- to 12-, and 3- to 12-μm spectral regions; and single-wavelength coating AR at 10.6 μm. Many other specialized wavelength bands are possible from 0.6 to 16 μm. 

Zinc Sulfide, Clear Grade 
• Also referred to as Cleartran* and multispectral zinc sulfide 
• A sort of CVD zinc sulfide that's further refined by a process that purifies the fabric and normalizes the crystal structure, which produces a uniform single crystal-like transmission throughout the whole VIS, MW, and LW spectral regions. 
• thanks to its good transmission within the VIS and IR, Cleartran is a perfect choice for systems with a clear camera and for various IR detectors or IR cameras. 
• Cleartan is about one-third harder than ZnSe. 
• Cleartran is about two-thirds the hardness of ZnS regular. 
• The relative price of Cleartran is about one-third quite ZnS regular; is about an equivalent as ZnSe and is usually quite Ge. 
• Diamond turnable 
• Low absorption and scatter properties over its relatively broad transmission range 
Transmission range 
0.4 to 12 μm 
Index of refraction 
2.350 @ 0.63 μm 
2.289 @ 1.06 μm 
2.252 @ 4 μm 
2.200 @ 10 μm 
dn/dT 
(avg. @ 298 to 358 K) 
54.3 × 10−6/K @ 0.6328 μm 
42.1 × 10−6/K @ 1.15 μm 
38.5 × 10−6/K @ 3.39 μm 
Density 
4.09 g/cm3 
Hardness (Knoop) 
160 kg/mm2 
Rupture modulus 
8704 psi 
Thermal expansion coefficient 
6.3 × 10−6/K @ 273 K 
7.0 × 10−6/K @ 373 K 
7.5 × 10−6/K @ 473 K 
Typical applications 
Visible imaging, thermal imaging FLIR, astronomy 
Products manufactured 
Lenses, aspheric lenses, binary (diffractive) lenses, windows, beamsplitters, and optical filters, and prisms 
Surface finish 
Typical specifications for surface quality are 40-20 scratch-dig within the 0.4- to the 3-μm spectral region and 60-40 or 80-50 scratch-dig within the 3- to 12-μm spectral region. Diamond-turned surface roughness of 100 Å RMS or better is typical. 
Surface figure 
In the VIS and NIR spectral regions, the specified surface figure ranges from 1/10 to 1/2 wave @ 0.6328 μm. In the IR, typically required surface figure ranges from 1/2 to 2 waves @ 0.6328 μm. 
AR coating options 
Typically available coatings include BBAR for the 0.8- to 2.5-, 3- to 5-, and 8- to 12-μm bands. Other specialized bands are possible from 0.4 to 12 μm. 

Zinc Sulfide (ZnS), Regular Grade 
• As a CVD material, ZnS regular grade has good imaging quality from 8 to 12 μm. It also transmits within the 3- to the 5-μm band, but with higher absorption and scatters than the Clear ZnS. 
• It exhibits high strength and hardness, and good resistance to hostile environments. 
• it's about one-third harder than Clear-tran and about twice as hard as ZnSe. 
• doesn't transmit well within the VIS spectral region 
• Relatively low cost of about two-thirds the worth of Cleartran or ZnSe 
• Diamond turnable 
Transmission range 
3 to 12 μm 
Index of refraction 
2.252 @ 4 μm 
2.200 @ 10 μm 
dn/dT 
(avg. @ 298 to 358 K) 
46 × 10−6/K @ 1.15 μm 
43 × 10−6/K @ 3.39 μm 
41 × 10−6/K @ 10.6 μm 
Density 
4.09 g/cm3 
Hardness (Knoop) 
200 kg/mm2 
Rupture modulus 
14,943 psi 
Thermal expansion coefficient 
6.6 × 10−6/K @ 273 K 
7.3 × 10−6/K @ 373 K 
7.7 × 10−6/K @ 473 K 
Typical applications 
Thermal imaging, FLIR 
Products manufactured 
Lenses, aspheric lenses, windows, domes, wedges, and prisms 
Surface finish 
Typical specifications for surface quality within the 3- to the 12-μm spectral region are 60-40, 80-50, or 120-80 scratch-dig. 
Surface figure 
In the IR, the typical surface figure is specified from 1/4 to 2 waves @ 0.6328 μm. 
AR coating options 
The most typical available coating specified for ZnS regular is BBAR for 8- to 12-μm regions. It also can be hard carbon or diamond-like carbon coated. 
 

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