Étalon–spectrograph system for improved resolution over a wide spectral range

In this system the Airy pattern from a scanning Fabry-Perot étalon is imaged onto the entrance slit of a diffraction grating spectrograph. The dispersed light from the spectrograph is, in turn, imaged onto a 500-channel vidicon tube for a digital output. If the free spectral range of the étalon is a few times greater than the wavelength dispersion per channel spacing on the vidicon, scanning the étalon across its free spectral range can reproduce the entire spectral region displayed by the spectrograph with approximately the resolution of the étalon.