Development and field tests of a narrowband all-reflective spatial heterodyne spectrometer.

Abstract

We describe the design, development, and performance of a narrowband, all-reflective, unaliased spatial heterodyne spectrometer (SHS) that has been tested in observations at the focus of the 1.6m main telescope of the McMath-Pierce solar telescope on Kitt Peak. The all-reflective SHS described herein is a highly robust common-path Fourier transform spectrometer without moving parts that, over a limited spectral region, combines the large field of view and high resolving power characteristic of interference spectrometers but at substantially reduced instrument size and optical tolerances. The self-scanned region of wavelength space and resolving power of the SHS are determined by the beam size, the diffraction grating groove density, the number of detector elements, and the fixed orientation of a set of pilot mirrors. The results presented here represent the first successful implementation of this reflective SHS design for field use. We discuss concepts behind the unaliased reflective SHS design and report the performance of the instrument when used to observe terrestrial airglow and absorption features, the solar spectrum, and the Jovian spectrum near λ=6300 Å, at the achieved resolving power (R=λ/δλ) of R>100,000. The results confirm that reflective SHS instruments can deliver effective interferometric performance in the visible to the far-ultraviolet wavelengths with commercial optics of moderate surface quality.