The performance of a double-beam fourier transform spectrometer and its application to the measurement of weak i.r. absorption

A double-beam, optically compensated, Fourier transform spectrometer is described. Its superiority in the investigation of weak spectral features has been demonstrated by the detection of 0.5 to ∼1% peak absorption in a narrow line due to small amounts of gaseous NH ₃. Moreover, the instrument has been applied to measure the disorder induced phonon absorption of a thin amorphous Ge film. The phase correction procedure, which has been developed for the compensating mode, is discussed.