Production of a High Resolving Power by means of Multilayer Coatings

Abstract

WHEN one applies the Fabry–Perot interferometer to absorption spectra, as has been done with some success in solar physics¹, high reflectivity and small absorption are essential if high resolving power is required. This is partly because one is compelled, in nearly all such cases, to use in combination with the interferometer a rather powerful auxiliary spectrograph, which in itself causes a considerable loss of light. Also, one can attain greater resolution only to a very limited degree by increasing the separation of the Fabry–Perot plates, because the greater separation reduces the range of the interferometer. It is well known that this range should be in a certain useful ratio to the intensity (or width) of the absorption line under investigation¹. There is, in addition, an important connexion between the maximum plate separation (which determines the range) and the instrumental line-width of the auxiliary spectrograph². The result is that in the visible spectrum the separation should not exceed about 10 mm. in air.