Summary Description

ZnSe is a medium refractive index material (2.4 @ 10 microns) with good long wavelength transmission in the infrared. It is a popular material choice for transmission analysis of aqueous samples as it is insoluble in water. ZnSe is a relatively hard and durable material, especially compared to potassium bromide (KBr) and therefore is widely used as a beamsplitter and for windows in portable infrared spectrometers. ZnSe is widely used as a material for attenuated total reflectance (ATR) measurements, offering good spectral range coverage and resistance to wear. It has replaced Ge in most military applications such as thermal imaging since it has no free carrier absorption at elevated temperature. ZnSe is also used in very high power laser systems such as laser machining.

Advantages

1. Zero water solubility
2. Good chemical resistance
3. Good spectral range Down to 500 cm^-1 for windows and 600 cm^-1 for beamsplitters
4. High refractive index permits design of excellent broad band anti-reflective (BBAR) coatings
5. Refractive index is almost identical to diamond thus can be combined with diamond in some unique designs
6. Most popular ATR spectroscopy material
7. Can be fabricated by diamond turning; thus can be fabricated into unique aspheric lenses
8. Available in very large sizes

Disadvantages

1. Attacked by strong acids and bases

Physical Data

Melting Point: 1526 °C
Density: 5.3 g/cm³
Solubility in H₂O: Insoluble
Hardness: 120 kg/mm²
Appearance: Yellow crystalline

Mid-IR Transmission – 4 mm thick ZnSe window

Refractive Index¹

Specific index listed; Generic: 2.40 @ 10 microns

Spectral Range

Short Wavelength Limit: 15,000 cm^-1 (1 mm)
Long Wavelength Limit: 461 cm^-1 (2 mm), 508 cm^-1 (4 mm)

Coatings

The infrared throughput of ZnSe can be significantly increased with application of specialized BBAR coatings to levels exceeding 95% transmission. It may also be coated to control depth of penetration in ATR applications.

Typical Uses

• IR transmission analysis
• IR detector windows
• ATR elements
• Condensing lenses
• Imaging lenses
• High power CO² lasers

Notes

Short and Long Wavelength Limits defined for which transmissivity is greater than 50% of stated crystal thickness.

1. Handbook of Optics, 3rd ed., Vol. 4, McGraw-Hill 2009