Zinc selenide

Material
ZnSe

 

Zinc selenide is the most popular material for Infrared application. Due to very wide transmission range covering 0.6µm to 20µm CVD grown ZnSe high optical quality material is used to manufacture optical components (windows, mirrors, lenses etc.) for high power IR lasers.

 

Zinc Selenide is produced by synthesis from zinc vapor and H2Se gas, forming as sheets on graphite susceptors. This material is soft and non-hygroscopic. It is microcrystalline in structure; the grain size being controlled to produce maximum strength. Single crystal ZnSe is available but is not common but has been reported as having lower absorption and thus more effective for CO2 optics.

 

The internal transmittance of Zinc Selenide is very high (absorption ≤0,0005cm-1 at 10.6µm), the relatively high refractive index (2.4 at 10.6µm) cause reflection losses of nearly 30%. Unless such losses can be tolerated, Zinc Selenide optics should always be antireflection coated. Because of the high refractive index, single- and double-layer antireflection coatings can be very effective.

 

Although Zinc Selenide has this clear advantage over Silicon and Germanium, unfortunately it is not an easy material from which to produce optics. Firstly, it is not a naturally occurring material and must be synthesized using a difficult process (CVD). Secondly, the dust, which is generated when Zinc Selenide is ground and polished, constitutes a significant health hazard as a cumulative toxin.

Properties
Optical properties
Transmission range in µm (minimum 10%)
0,48‐20
Transmission range in µm (minimum 50%)
0,5‐20
Refractive index @633nm
2,591

(2,403 @10,6µm)

Reflection losses in % at 1 surface
17,05 @10µm
Reflection losses in % at 2 surfaces
29,1 @10,6µm
dN/dT in 1/K
61 · 10-6 @10,6µm @298K
Physical properties
Density in g/cm3
5,27
Melting point in °C
subl. >500°C
Spezific heat capacity in J/(kg · K)
339
Thermal conductivity in W/(m · K)
18
Thermal expension in 1/K
7,1 · 10-6 @271K
Dielectric constants
9,12
Solubility in water in g/100g
insoluble
Mohs hardness
4
Knoop hardness in kg/mm²
110
Material type
polycrystalline, synthetic
Crystal type
cubic, zincblende structure
Crystal structure
F43m
Lattice constant in Å
a = 5,67
Elastic coefficient in GPa
C11 = 86,4

C12 = 51,5

C44 = 40,2

Young's Modulus (E) in Gpa
70,3
Shear Modulus (G) in GPa
28,9
Bulk Modulus (K) in GPa
63,1
Rupture Modulus in MPa
55
Apparent elastic limit in MPa
55,1
Poisson ratio
0,3
Spectral properties
Optical Properties
Transmission range in µm @10% min. 0.48 - 20
Transmission range in µm @50% min. 0.5 - 20
Refractive index @ 633nm 2.5906
(2.4028 @10.6µm)
Reflection losses in % at 1 surface 17.05 @ 10µm
Reflection losses in % at 2 surfaces 29.1 @ 10.6µm
dn/dT in 1/K 61 · 10-6
Physical Properties
Density in g/cm³ 5.27
Melting point in °C Subl. @ >500
Specific heat capacity in J/(kg · K) 339
Thermal Conductivity in W/(m · K) 18
Thermal Expansion in 1/K 7.1 · 10-6 @ 271K
Dielectric constant 9.12
Solubility in water in g/100g unsoluble
Mohs hardness 4
Knoop hardness in kg/mm² 110
Material type Polycrystalline, synthetic
Crystal type cubic
Crystal structure F43m
Lattice constant in Å a = 5.67
Elastic coeficients in GPa C11 = 86.4
C12 = 51.5
C44 = 40.2
Young's Modulus (E) in GPa 70.3
Shear Modulus (G) in GPa 28.9
Bulk Modulus (K) in GPa 63.1
Rupture Modulus in MPa 55
Apparent elastic limit in MPa 55.1
Poisson ratio 0.3
Spectral Properties