The authors present a new concept for a spectrometer adapted to low light level, high-speed operation and low spectral resolution. It is based on a spatially modulated Mach-Zehnder Fourier transform interferometer, with a new arrangement to record the fringes. The interferogram is sensed by the use of a focal plane array tilted with respect to the fringe axis. This technique allows oversampling of the fringe pattern, which eliminates spectral aliasing that occurs with the conventional configuration. It extends the free spectral and dynamic range. © 1998 Society of Photo-Optical Instrumentation Engineers.