Infrared sensor with multiple sources for gas measurement

A method of detecting a gas, comprising:

• exciting a first energy source positioned within an enclosure such that energy from the first energy source impinges upon a mirror system positioned external to the enclosure and spaced from the enclosure, the mirror system reflecting energy from the first energy source to at least one detector system positioned within the enclosure via a first analytical path,
• exciting at least a second energy source positioned within an enclosure such that energy from the second energy source impinges upon the mirror system, the mirror system reflecting energy from the second energy source to the at least one detector system via a second analytical path, which is different from the first analytical path, each of the first analytical path and the second analytical path being less than two feet in length, a length of the first analytical path within the enclosure being less than 10% of a total length of the first analytical path, and a length of the second analytical path within the enclosure being less than 10% of a total length of the second analytical path;
• and
• determining a concentration of the gas based upon an analytical signal output from the detector system corresponding to the first analytical path and an analytical signal output from the detector system corresponding to the second analytical path.