Analytical description of a Fabry-Perot spectrometer. 9: Optimum operation with a spherical etalon

An analytical definition is developed for optimized operation of a Connes spherical etalon (CSE) (1958) which is independent of the angle of incidence of the light entering a Fabry-Perot spectrometer (FPS) used for measuring atmospheric parameters. Techniques are presented for deriving values for the etalon aperture, width and linewidth which are associated with minimal uncertainties for the Doppler widths (temperatures) and the shifts (wind speeds). Corresponding values are also calculated for the reflectivity and the finesse and used to establish an optimum value for the CSE gain factor. The results indicate that an etalon with a spherical aperture can be smaller and more powerful than a plane spectrometer with a larger aperture.