Reflective Neutral Density Filters
• Optical densities from 0.1 to 4
• Wavelength insensitive transmission
• Useable over 280-2000 nm
There are two ways to achieve neutral attenuation: reflection or absorption of the unwanted light. These Ealing reflective filters use a layer of inconel on a flat polished substrate. Inconel has the property that it is neutral over a large wavelength range. It also adheres well and can be controllably deposited to assure precise reflectance and transmittance values. These filters are supplied on fused silica substrates. The fused silica substrates will cover D = log10 Io It a wavelength range from 280 nm-2 μm. Since the attenuation mechanism is reflection these may also be used as effective beamsplitters.
Neutral density filters are normally specified in terms of their optical density which is defined as the logarithm of the ratio of intensities in the incident and transmitted beams as follows:
D = log10(Io/It)