A Fourier transform infrared spectrometer includes a beam splitter (22), end mirrors (21, 23), one of which may be scanned, and detectors (32) detecting the interfered light at the two outputs of a beam combiner (22), which may be the same optical element as the beam splitter (22). Time records of detector samples may be transformed by Fourier transform to obtain the corresponding spectra. The detectors (32) may be sampled alternately in time and the samples subsequently interleaved to provide an increased effective sampling rate. The detectors (32) may be masked by color filter mosaics so that each pixel of each detector is sensitive only to one color of light, and the spectra obtained from pixels detecting different colors may be concatenated.