Popular Design for Narrow Band Interference Filter - Ge Windows – Dien

The Germanium as a mono crystal primarily used in semi-conductor is non-absorptive at 2μm to 20μm IR regions. It is used here as an optical component for IR region applications.
Germanium is a high index material that is used to manufacture Attenuated Total Reflection (ATR) prisms for spectroscopy. Its refractive index is such that Germanium makes an effective natural 50% beamsplitter without the need for coatings. Germanium is also used extensively as a substrate for production of optical filters. Germanium covers the whole of the 8-14 micron thermal band and is used in lens systems for thermal imaging. Germanium can be AR coated with Diamond producing an extremely tough front optic.
Germanium is grown using the Czochralski technique by a small number of manufacturers in Belgium, USA, China and Russia. The refractive index of Germanium changes rapidly with temperature and the material becomes opaque at all wavelengths a little above 350K as the band gap floods with thermal electrons.
Application:
• Ideal for near-IR applications
• Broadband 3 to 12 μm anti-reflection coating
• Ideal for applications requiring low dispersion
• Great for low power CO2 laser applications
Feature:
• These germanium windows do not transmit at 1.5µm region or below, therefore its main application is in the IR regions.
• Germanium windows can be used in various infrared experiments.