D55mm Germanium wafer with AR coating

Germanium Windows are available with three anti-reflection coating options, 3 – 5μm for mid-infrared applications, 3 – 12μm for broadband multispectral applications, and 8 – 12μm for thermal imaging applications.
Ge wafer on picture is diameter 55mm 1mm thickness, both surfaces with AR coating at 7μm – 14μm, Tavg >95%.

Due to its high index of refraction, an anti-reflection coating is recommended on these ge windows for sufficient transmission. Germanium is subject to thermal runaway, meaning that the transmission decreases as temperature increases. As such, these germanium windows should be used at temperatures below 100°C. High density (5.33 g/cm³) of germanium should be considered when designing for weight-sensitive systems. The Knoop Hardness of germanium (780) is approximately twice that of magnesium fluoride, making it ideal for infrared applications requiring rugged optics.

Property of Germanium

• Clear Aperture (%): 90.00
• Dimensional Tolerance (mm): +0.0/-0.1
• Coefficient of Thermal Expansion CTE (10^-6/°C): 6.1
• Density (g/cm³): 5.33
• Index of Refraction n_d: 4.002 @ 11µm
• Knoop Hardness (kg/mm²): 780.00
• Parallelism (arcmin): <1
• Poisson’s Ratio: 0.28
• Substrate: Germanium (Ge)
• Surface Quality: 60-40
• Thickness Tolerance (mm): ±0.1

VY Optics also supply precision windows fabricated from several other substrates for use in a large variety of laser and industrial applications.