Time-resolved Fourier spectroscopy*†

Fourier spectroscopy has enjoyed considerable success in the measurement of sources that are stationary with respect to time. A technique for the study of time-varying spectral features, by use of Fourier spectroscopy, is presented. With this technique, the multiplex advantage is retained and the available measurement time is utilized efficiently. The technique consists of obtaining a series of interferograms, separated sequentially in time, according to the time-resolution capability of the detection system. The interferogram signal is recorded over a time interval, Δt, corresponding to a particular time tj, in the evolution of the source. The entire series of interferograms is obtained in a single scan of a Michelson interferometer. The S/N may be improved by continued exposure at the same optical path difference, corresponding to the same tj in the evolution of the source. The time-sequenced interferograms are transformed to obtain the recovered spectra at successive time intervals. As a demonstration of the technique, the spectral evolution of a N2/O2 gas mixture subjected to high-energy-electron irradiation is given in 50 µs intervals. The spectra clearly show the change in time of the fundamental sequence of NO (X2Π, Δν = 1), and the (001 → 000) vibration–rotation bands of N2O and NO2.