The Diffraction-Limited Near-Infrared Spectropolarimeter (DL-NIRSP) of the Daniel K. Inouye Solar Telescope (DKIST)

Abstract The Diffraction-Limited Near-Infrared Spectropolarimeter (DL-NIRSP) is one of the first-light instruments for the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST). DL-NIRSP is an integral-field, dual-beam spectropolarimeter intended for studying magnetically sensitive spectral lines in the Sun’s photosphere, chromosphere, and corona with high spectral resolution and polarimetric accuracy. Two novel fiber-optic integral-field units (IFUs), paired with selectable feed optics and a field-scanning mirror provide great flexibility in spatial sampling ( $0.03^{\prime\prime}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>0.03</mml:mn><mml:mrow><mml:mo>″</mml:mo></mml:mrow></mml:msup></mml:math> , $0.08^{\prime\prime}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>0.08</mml:mn><mml:mrow><mml:mo>″</mml:mo></mml:mrow></mml:msup></mml:math> , and $0.5^{\prime \prime}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>0.5</mml:mn><mml:mrow><mml:mo>″</mml:mo></mml:mrow></mml:msup></mml:math> ) and field coverage ( $2^{\prime} \times 2^{\prime }$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>2</mml:mn><mml:mo>′</mml:mo></mml:msup><mml:mo>×</mml:mo><mml:msup><mml:mn>2</mml:mn><mml:mo>′</mml:mo></mml:msup></mml:math> ). The IFUs allow DL-NIRSP to record all the spectra from a 2D field of view simultaneously, enabling the instrument to study the evolution of highly dynamic events. The spectrograph is an all-reflecting, near-Littrow design, which achieves a resolving power of approximately 125,000. Multiple wavelengths can be observed simultaneously using three spectral arms: one for visible wavelengths (500 – 900 nm) and two for infrared wavelengths (900 – 1350 nm and 1350 – 1800 nm). Each supporting camera sub-system is capable of a 30-Hz frame rate, making it possible to track dynamic phenomena on the Sun.