Use of selected glass types and glass thicknesses in the optical path to remove cross sensitivity to water absorption peaks

An infrared detector comprising:

• a light source configured to emit light;
• one or more sensors configured to receive at least a portion of the light emitted by the light source;
• and
• a filter glass located in an optical path between the light source and the one or more sensors, the filter glass having spectral absorption properties with regard to the light emitted, the spectral absorption properties being dependent upon at least a thickness of the filter glass and a composition of the filter glass,
• wherein the thickness of the filter glass is between 1 millimeter and 3 millimeters;
• wherein the filter glass comprises one or more materials that contain hydroxyls in their molecular structure, the one or more materials comprising Fused Silica, the thickness and composition of the filter glass being operable to filter out wavelengths less than 2900 nm and greater than 4100 nm from the light emitted by the light source, and
• wherein filtering out the wavelengths less than 2900 nm and greater than 4100 nm from the light filters out wavelengths that would be absorbed by water and carbon dioxide along the optical path and reduces the infrared detector's cross sensitivity to water and carbon dioxide.