4.1 EXES Instrument Overview

The Echelon-cross-Echelle Spectrograph (EXES) operates in the 4.5 ‒ 28.3 μm wavelength region, at high (R ≈ 50,000 ‒ 100,000), medium (R ≈ 5000 ‒ 20,000) and low (R ≈ 1000 ‒ 3000) spectral resolution. The instrument uses a 1024x1024 Si:As detector array. High resolution is provided by an echelon ‒ a coarsely-ruled, steeply-blazed aluminum reflection grating ‒ along with an echelle grating to cross-disperse the spectrum. The echelon can be bypassed so that the echelle acts as the sole dispersive element. This results in single order spectra at medium- or low-resolution depending on the incident angle.

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