At the heart of every FTIR is an optical device called an interferometer. A diagram of an interferometer is shown in Figure 2.1.

Can interferometer or “interference meter,” measures the interference pattern between two light beams. The light from an infrared source is shown entering the interferometer from the left in Figure 2.1. The interferometer splits the single light beam into two light beams. The interferometer then causes the two light beams to travel different paths, which are denoted D1 and D2 in Figure 2.1. After the two light beams have traveled their different paths they are recombined into one beam, and then the light beam leaves the interferometer in Figure 2.1.