Mask for Selecting Orders for Use with the Jarrell—Ash Order Sorter

Abstract

An inherent disadvantage in working at relatively high grating angles in optical emission spectroscopy in order to obtain increased dispersion and higher line-to-background ratios is the presence of multiple orders. If a stigmatic spectrograph (e.g., Jarrell-Ash 3.4-m Ebert) is used, the various orders can be offset or “sorted” by a device such as the Jarrell-Ash “order sorter.”1 The “order sorter” is essentially a low-dispersion spectroscope which projects a vertical spectrum of the source on the slit of the spectrograph. Light of wavelength λ falls on a specific portion of the slit while light of another wavelength, for example 2λ, falls on a different portion. If the spectrograph is stigmatic, the two wavelengths produce images at different levels on the photographic plate corresponding to their different positions on the slit; the length of each image being determined by the width of the “order sorter” slit. In this manner, the spectrum is “sorted” and overlapping orders avoided. However, the multiple orders are still in the focal plane to be recorded by the detector.