We have constructed an interferometric spectrometer in millimeter and submillimeter range (2_??_11cm-1). It consists of a continuous light wave source from a backward wave oscillator and its frequency multipliers, a symmetric Mach-Zehnder type interferometer, and a detection system. Analytical methods were developed to obtain optical constants rapidly and accurately. The refractive index and extinction coefficient were measured for several materials and the characteristics of the constracted spectrometer were evaluated.
