Optical attenuator prism characteristics
Optical attenuators are use to reduce the amount of light in an optical path. They can be shaped according to your needs to fit in your optical system.
Optical attenuator material
Attenuator are defined by their Optical density or absorbance of light. The acronym for Optical Density is OD, and usually optical attenuators are defined with a OD value.
The OD value is calculated at the logarithmic ratio of the light that will go through the material. The higher the value the lower the amount of light going through.
In short to avoid equation the number after the OD correspond to the exponent X in below equation :
ODx = Input light / 10^x
So an OD6 attenuator will divide the input light by 10^6 or 1,000,000, so one photon in one million will go through it.