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This gives the basic ideas, but the assumptions are shaky, so you might want a real derivation. This requires a resolvance of Fabry-Perot resolutionĪn approximate development of the resolvance expression can be done by using the small angle approximation to the condition for maxima. The red lines of hydrogen and deuterium are at 656.3 nm and 656.1 nm, respectively. Resolving them corresponds to resolvanceĪnother standard example is the resolution of the hydrogen and deuterium lines, often done with a Fabry-Perot Interferometer. The two sodium "D-lines" are at 589.00 nm and 589.59 nm. Where N is the total number of slits illuminatedand m is the order of the diffraction.Ī standard benchmark for the resolvance of a grating or other spectroscopic instrument is the resolution of the sodium doublet. This leads to a resolvance for a grating of Since the space between maxima for N slits isbroken up into N-2 subsidiary maxima, thedistance to the first mimimum is essentially1/N times the separation of the main maxima. The limit of resolution is determined by the Rayleigh criterion as applied to the diffraction maxima, i.e., two wavelengths are just resolved when the maximum of one lies at the first minimum of the other. Resolvance or "chromatic resolving power" for a device used to separate the wavelengths of light is defined as Examples of resolvance

Diffraction grating resolution Resolvance of Grating