Infrared Imaging Spectroscopy Using Massively Multiplexed Slit-Based Techniques and Sub-Field Motion Correction

Abstract

Targeting dynamic spatially-extended phenomena in the upper solar atmosphere, a new instrument concept has been developed and tested at the Dunn Solar Telescope in New Mexico, USA, that provides wide-field, rapid-scanning, high-resolution imaging spectroscopy of the neutral helium $\lambda10830$ spectral triplet. The instrument combines a narrowband imaging channel with a novel, co-spatial, 17 parallel-long-slit, grating-based spectrograph that are simultaneously imaged on a single HgCdTe detector. Over a $170'' \times 120''$ field of view, a temporal cadence of 8.5 seconds is achieved between successive maps that critically sample the diffraction limit of the Dunn Solar Telescope at 1083 nm ($1.22 \lambda/D = 0.36''$) and provide a resolving power ($R = \lambda / \delta\lambda$) up to $\sim25000$ with a 1 nm bandwidth (i.e., 275 km sec$^{-1}$ Doppler coverage). Capitalizing on the strict simultaneity of the narrowband channel relative to each spectral image (acquired at a rate of 10 Hz), this work demonstrates that sub-field image motion introduced by atmospheric seeing may be compensated in each mapped spectral data cube. This instrument furnishes essential infrared spectral imaging capabilities for current investigations while pioneering techniques for high-resolution, wide-field, time-domain solar astronomy.