TABLE OF CONTENTS Fourier transform spectroscopy (FTS) is a nondispersive spectroscopic method, although with considerable difference in theory to the nondispersive filters presented above. The principles of operation, utility of liquid crystals in, and applications of such devices are highlighted.
There are two general types of Fourier transform (FT) spectrometers, one based on a Michelson interferometer and one based on coupled polarizers and retarders, similar in some facets to the Lyot filter presented in Section 3.2.4. In the first case, source irradiation is propagated through, or reflected from, the specimen of interest and then projected into one arm of a standard Michelson interferometer. As is shown in Figure 3.20(a), the beam is divided into two equal parts using a beamsplitter, with one beam propagating to a stationary mirror and other beam propagating to an axially scanning mirror. As the scanning mirror moves, a phase modulation, ? 
, is created between the two beams depending on the optical path difference between the pathways. The two beams are recombined using the same beamsplitter and the interference effects are monitored on a single point photodetector. The absolute phase delay is the same for all spectral components, creating frequency dependent constructive and destructive interference after recombination at the output arm. The superposition of the interference pattern from all frequency components appears superimposed into one interferogram, which can be transformed from a scanning mirror position versus intensity plot into a frequency versus intensity plot using a Fourier transform. In...
