A closed path infrared sensor includes an enclosure, a first energy source within the enclosure, at least a second energy source within the enclosure, at least one detector system within the enclosure and a mirror system external to the enclosure and spaced from the enclosure. The mirror system reflects energy from the first energy source to the at least one detector system via a first analytical path and reflects energy from the second energy source to the at least one detector system via a second analytical path. Each of the first analytical path and the second analytical path are less than two feet in length.