Fabry-perot interference spectrometer

PURPOSE:To relax the positioning precision of light path length selection, by inserting movably one wedge-shaped dielectric of a prescribed vertical angle or two prescribed wedge-shaped dielectrics in the vertical direction between two parallel or inclined reflection faces of the Fabry-Perot interference spectrometer. CONSTITUTION:Partial reflection faces are provided on inside faces 3 and 4 of dielectric plates 1 and 2 with both faces polished optically and make angle alpha. Wedge-shaped dielectric 50 of prescribed vertical angle beta is inserted movably between them in the (x) direction. If alpha and beta are so set that tan beta/2 may be equal to the value obtained by dividing sinalpha/2 by (n-cosalpha/2), change DELTAx in the (x) direction of dielectric 50 is relaxed by 1/sinalpha/2 times in comparison with interval change of the normal interferometer. If wedge-shaped dielectrics 50b and 50c of refractive index (n) and vertical angle gamma are inserted in directions opposite to each other between two parallel reflection plates 1 and 2, the above-mentioned change is relaxed by 1/n tangamma times. As a result, the same light path length can be maintaned stably, and the light of a specific wave length can be permit to pass through continuously in respect to time.