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UV-IR Optics

MgF2 is a birefrigent material crystal with excellent physical and chemical properties. It provides wide transparent range, high transmissibility. MgF2 is a rugged material resistant to chemical etching, mechanical, and thermal shock. High vacuum UV transmission and resistance to laser damage make MgF2 a popular choice for VUV and excimer laser windows, polarizers, and lenses.

Main Properties of MgF2

Lattice constanta=4.621A; c=3.053A
Melting Point1255℃
Density3.17g/cm3 (at 291K)
Mohs hardness6
Thermal conductivity0.3 Wm-1K-1
Expansion coefficientaa=13.7x10-6/K; ac=8.48x10-6/K
Elastic CoefficientsC11=140.2 C12=89.5 C44=56.8
Transparence range0.11-7.5µm
Refraction Index@405nm no=1.3836, ne=1.3957

Specification of MgF2 Window

Diameter Tolerance+0.0/-0.1mm
Thickness Tolerance+/-0.1mm
Flatnessλ/4 at 632.8nm
Surface Quality40-20
Parallelism<3 arc min
Clear Aperture >90%



Calcium Fluoride (CaF2) is a crystal which has good transmission from 170nm to 7800nm. It is slightly soluble in water and is susceptible to thermal shock. Common uses of CaF2 include IR components such as windows, lenses and Prisms.

Main Properties of CaF2

Melting Point1360℃
Density3.18g/cm3 (at 291K)
Mohs hardness4
Thermal conductivity9.71 Wm-1K-1
Expansion coefficient18.85x10-6/K
Elastic CoefficientsC11=164 C12=53 C44=33.7
Transparence range0.13-10µm
Refraction Indexn=1.6921-1.3161

Specification of CaF2 Window 

Diameter Tolerance+0.0/-0.1mm
Thickness Tolerance+/-0.1mm
Flatnessλ/4 at 632.8nm
Surface Quality40-20
Parallelism<3 arc min
Clear Aperture >90%



Silicon (Si) is commonly used as a substrate material for infrared reflectors and windows in the 1.5μ m-8μm region. The strong absorption band at 9μm makes it unsuitable for CO2 laser transmission applications but it is frequently used for laser mirrors because of its high thermal conductivity and low density. Silicon is also a useful transmitter in 20μm range.
    Silicon is the most abundant electropositive element in the Earth’s crust. It’s a metalloid with a marked metallic luster and very brittle. It is usually tetravalent in its compounds, although sometimes they are bivalent and purely electropositive in its chemical behavior. Moreover, pentacoordinated and hexacoordinated silicon compounds are also known.
    Silicon lenses are popular for many applications in the IR. They are typically used for imaging applications in the 3-5μm region of the spectrum, making them excellent for security and military applications. They can also be used to collimate infrared lasers. These lenses are coated with a BBAR coating that provides 98% transmission in the 3-5μm spectral range.

Main Properties of Si

Material TypeCZ FZ,N or P
Crystal Direction[100],[111]
Resistivity0.003-50 Ohm/cm
Melting Point1410℃
Knoop Hardness1150kg/mm2
Thermal Conductivity163.3 J/k.m.s@273K
Transmittance Range1um-10um,30um-300um
Refraction Index3.4179@10µm

Specification of Si Window & Mirror

Diameter Tolerance+0.0/-0.1mm
Thickness Tolerance+/-0.1mm
Flatnessλ/8 at 632.8nm
Surface Quality40-20
Parallelism<3 arc min
Clear Aperture >90%
CoatingAR or HR coating



Germanium (Ge) is used widely for lenses and windows in thermal imaging and FLIR applications. Its high index of refraction makes it of particular interest. Useful transmission range of Germanium windows is from 2 to 12μm.Germanium is opaque in the visible.
    Germanium has the property of thermal runaway, meaning that the transmission decreases as temperature increases. As such, Ge window should be used at temperatures below 100°C. The higher Knoop Hardness of Germanium (780) makes it ideal for IR applications requiring rugged optics. Germanium’s high density (5.33/cm 3) should be considered when designing for weight-sensitive systems.

Main Properties of Ge

Material TypeN or P
Resistivity4-50 Ohm/cm
Knoop Hardness780kg/mm2
Thermal Expansion Coefficient5.5x10-6/K
Transmittance Range2µm-4µm
Refraction Index4.003@10µm

Specification of Ge Lens 

Diameter Tolerance+0.0/-0.1mm
Thickness Tolerance+/-0.1mm
Flatnessλ/4 at 632.8nm
Surface Quality40-20
Parallelism<3 arc min
Clear Aperture >90%
Coating AR or BBAR coating



ZnSe is used for optical windows, lenses, mirrors, prisms and optical blanks, plates, disks, sheets, slabs particularly for infrared applications Zinc Selenide (ZnSe) — transparent in wide spectral range from yellow (visible) to far IR. ZnSe material is a chemically inert, non-hygroscopic and highly pure product that is very effective in many optical applications due to its extremely low bulk losses, high resistance to thermal shock and stability in virtually all environments, easily machined. To obtain superior transmittance, ZnSe crystals are grown by Chemical Vapor Deposition process (CVD). Zinc Selenide CVD is polycrystalline material, demonstrates superior CO2 laser transmittance and is employed in the transmission optical components used in CO2 laser processing. ZnSe (Zinc Selenide) Chemical Vapor Deposition (CVD) material is produced by synthesis from zinc vapour and H2Se gas, forming as sheets on graphite susceptors (ZnSe-CVD processes). Chemical purity of CVD-ZnSe 99.999%. It has à polycrystalline structure; the grain size of Zinc Selenide CVD material is controlled to produce maximum strength. The transmission range of Zinc Selenide ZnSe-CVD is (0.5 – 20) microns. ZnSe CVD used for high power CO2 laser optics at 10.6 microns, for protective optics windows or optical elements in FLIR (forward looking infrared) thermal imaging equipment, optics for medical and industrial applications (optical plane parallel windows (plates, disks, sheets, slabs, blanks), wedged windows, Brewster windows, optical meniscus, spherical and cylindrical lenses, prisms, resonator mirrors of CO2 laser). Single crystal ZnSe Zinc Selenide is available, but is not common, it has lower bulk losses and thus more effective for CO2 optics.

Main Properties of ZnSe(CVD)

Density5.27 g/cm3
Melting Point1525℃
Thermal Conductivity18 W/(m K)@298K
Thermal Expansion7.1 x 10-6/℃ at 273K
Hardness339 J/(kg K)
Transmission Range0.6-21.0µm
Refractive Index2.4028@10µm

Specification of ZnSe Lens 

Design Wavelength10.6µm
Focal Length Tolerance+/-1%
Diameter Tolerance+0.0/-0.1mm
Thickness Tolerance+/-0.1mm
Flatnessλ/4 at 632.8nm
Surface Quality40-20
Centration<3 arc min
Clear Aperture >90%
CoatingAR@10.6µm or BBAR@8-14µm


Toptec Optics, Inc.

Tel:+86-591-8347 7500

Fax:+86-591-8347 7600

24 Baihuazhou Road,Pushang Industrial Park,Fuzhou 350008,China

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