Metallic-coated infrared neutral density filters (IR ND filters) obtain their optical density from a metal alloy coating on a substrate determined by the wavelength region of interest. Unlike the all-dielectric or absorption type, the metallic type ND filter employs a combination of absorption and reflection to reduce the intensity of light.
Infrared Neutral Density Filters are designed to attenuate radiation over a wide spectral range. These filters are coated on germanium substrates. The ND coating is optimized at 2.2 microns and can be used out to 15 microns.
