Critical Performance Differences Of Monocrystalline Versus Polycrystalline Germanium For Optical Applications

By D. Hibbard, B. Neff, B. Reinbolt, R. Klinger, and M. Stout

Germanium (Ge) is a useful optical material over the mid‐wave and long‐wave infrared wavelength region. It can be used as a window, dome or lens substrate, and it can be coated with thin film layers to enhance its optical performance and durability.

It can be obtained in the form of a single crystal or as polycrystalline material.

In general, polycrystalline germanium is less expensive and is available in larger sizes than monocrystalline material.

In a number of cases, it is worthwhile for an optical designer/fabricator to consider which material class is the better choice for a particular application. Generally, material suppliers can readily quantify one set of trade‐offs associated with material cost and availability. However, EEO has found that the corresponding trade‐offs related to technical performance differences are not well defined, at present.