Abstract: A switchable infrared radiation method and device provides for optical analysis of a sample using a Fourier transform spectrometer for illumination thereof. A housing accommodates an optical delineation means mounted therein which transmits infrared radiation following interaction with the sample. The radiation is passed through an optical switch mounted in the housing having a first switching position and a second switching position for reflecting infrared radiation transmitted by the optical delineation means. A single element detector is mounted in the housing for detecting infrared radiation transmitted by the optical switch in its first switching position. An array detector is also mounted in the housing to accept radiation from the optical switch in the second switching position. The array detector comprises a plurality of pixel-like infrared sensors for two-dimensional detection of the radiation.