Instrumentation optimization in fourier spectroscopy. 1: far infrared beam splitters

Computations of the reflectivity, transmissivity, and efficiency properties for TE, TM, and T45 degrees waves of far ir beam splitters (BS) and of the polarizations induced at both reflection and transmission are described. Effects of variations in the state of polarization, orientation, pointing accuracy, and wavelength of the incident light, as well as variations in refractive index and thickness of the BS, are discussed. These results apply directly to Fourier interferometer-spectrometers. They can be used for optimizingthe performance of these instruments. They indicate, in particular, that some advantages may begained by the use of incident polarized light (angle of polarization smaller than about 45 degrees or negative elliptical polarization) or light of large incidence angle (larger than approximately 60 degrees ) or both. A novel method of inversion of experimental results to the end of determining the BS physical parameters is proposed. It makes use of the variations with incident light direction of the BS reflectivity, transmissivity, or efficiency curves.