Low Noise Solar and Laboratory Spectroscopy: I. Technique

Abstract

A calculation of the theoretical signal to noise ratio for optical solar spectra formed by grating spectrographs is given, and it is shown that commonly observed spectra are more noisy than this limit by a factor of more than one hundred. A form of spectrometer designed to yield a low noise level is described. Examples of solar spectra obtained with this instrument are given and it is shown that their noise level is very close to the theoretical limit.