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, rapidscanning, high-resolution imaging spectroscopy of the neutral helium λ10830 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 × 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 (1.22λ/D = 0.36 ) and provide a resolving power (R = λ/δλ) up to ∼ 40000 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.

Neutral Helium Triplet Spectroscopy of Quiescent Coronal Rain with Sensitivity Estimates for Spectropolarimetric Magnetic Field Diagnostics

“…The MXIS experiment, described in detail by Schad & Lin (2017), provides rapid-cadence, wide-field imaging spectroscopy of He I 10830 Å by taking advantage of multiplexing techniques developed for full-disk spectroheliography (Lin 2014). It consists of two science channels-a grating-based spectrograph and a narrowband imager-simultaneously imaged on separate halves of a single 2048 × 2048 pixel HgCdTe detector.…”

“…The He I Doppler coverage is -195 to 85 km s −1 . The spectral pixel width is 120.4 m Å; though, spectral resolution is limited for the data described here by spectral focus aberrations suffered during this campaign, as discussed by Schad & Lin (2017) and carefully calibrated in Section 2.1.1. The slit width is ≈ 0.…”

“…Owing in large part to the use of novel multiplexed spectroscopic techniques (Schad & Lin 2017), the study presented here performs time-resolved spectroscopy of He I 10830 Å observed in quiescent coronal rain off-limb. This permits analysis of its evolving morphology as well as statistical quantification of its total integrated line radiance (brightness), spectral line width, and both its apparent and Doppler velocity characteristics.…”

The Multi-slit Approach to Coronal Spectroscopy with the Multi-slit Solar Explorer (MUSE)

“…A high-cadence alternative to using a raster with a single slit is to use multiple entrance slits to the spectrograph, each of which allows light from the telescope image to pass through for a different value of y. Such multi-slit spectrometers have been used at visible and (NIR) wavelengths for solar observations of Hα (Martin et al 1974) and He I 10830 Å (Schad & Lin 2017). Independent of details of how the optical system can be implemented for different wavelength regions, there is always the limitation of available detector real estate, that is, the number of resolution elements in the detector.…”

Shock Heating Energy of Umbral Flashes Measured with Integral Field Unit Spectroscopy

“…The IFU also allows us to observe the entire sunspot efficiently with a short enough cadence to resolve the shock dynamics, and it enables us to compare the spatial distribution of shock properties with that of heating signatures. This IFU technique for such high cadence imaging spectroscopy represents a new class of solar instruments based on multiplexed diffraction-grating-based spectrographs (Jaeggli et al 2010;Lin 2014;Schad & Lin 2017;Jurčák et al 2019). Below we describe details regarding the observations (Section 2), the determination of the Mach number and the temperature upstream of the shock (Section 3), and the results of the shock heating energy rate derived from the shock characteristics (Section 4).…”