The circularly symmetric grille spectrometer.

A grille spectrometer, with grilles formed of alternately transparent and nontransparent concentric circular zones, has been constructed. The quantity of light that can be accepted from an extended source with such an instrument is orders of magnitude greater than that of a slit spectrometer with the same resolution, and greater even than that of a scanning Fabry-Perot spectrometer of the same resolution. For extended sources of brightness insufficient to bring the photon shot noise above detector noise, the grille spectrometer offers an advantage over the slit spectrometer and Fabry-Perot in greater signal to noise. In cases where the photon shot noise is greater than the detector noise, the better signal to noise applied for emission-line sources, and also for continuum sources if a large interference filter premonochromator is used. The spectrometer is being used in airglow observation.