Reduction of multiple reflections in infrared-imaging Fourier transform spectrometers

The causes and effects of multiple reflections which occur in the beam splitter component of imaging Fourier Transform Spectrometers (FTSs) are investigated with the objective of determining methods to improve the quality of the data obtained from these instruments.; A complete literature review is included that addresses the history of interferometery, the theory of interferometry, beam splitters, field widening in FTSs, hyperspectral imaging, imaging spectrometers, image abnormalities, and mathematical modeling of interferometers.; The differences between imaging and non-imaging FTSs as well as their respective susceptibilities to multiple reflection problems are explored. Eight alternative beam splitter/compensator configurations for use in infrared imaging Fourier transform spectrometers are then presented. The objective is to identify one or more configurations that may reduce multiple reflection problems. The advantages and disadvantages of the eight configurations are compared and three characteristics are identified that are primary factors in reducing susceptibility to multiple reflections. These three characteristics are: (1) widened air gap, (2) small angles of incidence, and (3) antireflection coatings on aircalcium fluoride boundaries.; An improved beam splitter design is identified that combines the best qualities of the eight beam splitter configurations. The improved beam splitter design is then analyzed and compared to a “baseline” beam splitter design typical of current non-imaging FTSs. The comparison includes the results of a computer simulation of the baseline and improved designs.; The improved beam splitter shown to generate 77% fewer reflections overall and 69% fewer detector incident reflections than the baseline beam splitter. Also, the reflections that are incident on the detector in the improved beam splitter are shown to be at least a factor of ten lower in power than those in the baseline beam splitter.