Fourier-transform spectroscopy using liquid-crystal technology

We report the use of a ferroelectric liquid-crystal (FLC) mask as an optical encoder for development of a solid-state Fourier-transform spectrometer. For this demonstration a 1 x 64 element array was striped and used as a 1 x 4 element device. The device intersected dispersed radiation and encoded each spectral component with a carrier signal by applying half-wave potential to each of the four striped (1 x 16) FLC elements, which varied the transmitted amplitude of the light from 0.03% to 28% of full scale. The light was spectrally recombined and imaged onto a photomultiplier and the resulting carriers (and their amplitudes) detected by Fourier transformation of the time-varying signal. Spectra of colored-glass filters were taken to demonstrate the possibilities of the instrument.