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   ICON ZnSe single crystal CVD
 
 
 
 

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 high transmittance ZnSe crystals are grown by Chemical Vapor Deposition process (CVD). CVD Zinc Selenide is polycrystalline material which is used in the optical components of CO2 laser systems and IR optical devices.

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 a polycrystalline structure; the grain size of Zinc Selenide CVD material is controlled to produce maximum strength and machinability.

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), domes, 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.

 
Description  
 

ZNSE (ZINC SELENIDE) BASE PROPERTIES

PARAMETER VALUE
PHYSICAL PROPERTIES of Zinc Selenide (ZnSe)  
  Density   5.27 g/cm3  
  Melting Point   1525 ° C (dissociates about 700 ° C)  
  Thermal Conductivity   18 W/(m K) at 298K  
  Thermal Expansion   7.1 x 10 -6 / ° C at 273K  
  Hardness Knoop, with 50 g indenter, kg/mm2   120  
  Specific Heat Capacity   339 J/(kg K)  
  Young's Modulus (E)   67.2 GPa  
  Bulk Modulus (K)   40 GPa  
  Apparent Elastic Limit   55.1 MPa (8,000psi)  
  Poisson Ratio   0.28  
  Resistivity   ~1012 (Ohm x cm)  
CHEMICAL PROPERTIES of Zinc Selenide ZnSe CVD  
  Solubility   0.001 g/100g water  
  Molecular Weight   144.33  
  Crystal Structure   Cubic, “zincblende” structure, polycrystalline CVD ZnSe grain size (50-70) microns  
OPTICAL PROPERTIES of ZnSe Zinc Selenide CVD  
  Transmission Range   (0.5 - 20) microns  
  Refractive Index   2.4028 at 10 microns  
  Reflection Loss   29.1% at 10.6 µm (2 surfaces, with subsequent multiple internal beam reflections)  
  dn/dT   + 61 x 10 -6 / °C at 10.6 microns at 298K  
  dn/dµ = 0   5.5 µm  
  Index of Absorption   0.0005 (1/cm) at 10.6 microns, ZnSe-CVD Laser grade  

ZNSE (ZINC SELENIDE) REFRACTIVE INDEX

  Wavelength, µm 2.75 5.00 7.50 9.50 11.0 12.5 13.5  
  Refractive Index 2.44 2.43 2.42 2.41 2.40 2.39 2.38  
  Wavelength, µm 15.0 16.0 16.9 17.8 18.6 19.3 20.0  
  Refractive Index 2.37 2.36 2.35 2.34 2.33 2.32 2.31  


TRANSMISSION of UNCOATED and AR/AR COATED ZNSE OPTICS 

Because of high refractive index (n = 2.4 at 10.6 microns), calculated Fresnel losses of Zinc Selenide polished surface are equal 17% (at one side), thus the transmission (T) of ZnSe polished window equals T = 68.9 % at 10.6 micron (without absorption). Note all calculations are done for wavelength of CO2 laser 10.6 microns leaving out of account the possible multiple internal beam reflections. 

. If ZnSe window is a plane parallel plate and laser beam with good (plane wave) incidences perpendicularly to a ZnSe window surface (normal incidence), in this case we must take into account subsequent multiple internal beam reflections inside of ZnSe plate. So transmission (Tw) of a uncoated ZnSe window subject to multiple reflections (5 times) will be 1.03 times more, namely Tw = 70.9% (without absorption). Hence Reflection Loss in this case equals 29.1%. Even if one of mentioned above conditions is absent, transmission of Zinc Selenide window will equal T = 68.9 % at 10.6 micron (without absorption). As to another wavelength 13.5 microns refractive index n = 2.38, so T = 69.4% (without absorption) and Tw = 71.4% (without absorption). You can see spectrum transmission chart of ZnSe window below. 

Spectral Transmittance (T) of CVD-ZnSe Uncoated Polished Windows: first - thickness 5mm for range (400 - 1100) nm, second - thickness 10mm for range (2.5 - 25) microns and third - thickness 20mm for range (200 - 1100) nm.


 
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