Photon Sieves, EUNIS, and the Future of EUV Spectroscopy

The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) is a two-channel imaging spectrograph with unprecedented dynamic range and broad spectral coverage (9-11 nm and 52-64 nm), scheduled for a sounding rocket flight in November 2018. This will be the first time the 9-11 nm wavelength range of the Sun has ever been observed by an imaging spectrograph, despite the importance of these short EUV/soft X-ray wavelengths to observing the hottest (>5MK) plasma in the non-flaring atmosphere, which is critical to understanding the energization of the solar corona. The ability to observe this important spectral region is made possible by recent developments in EUV optical coatings and gratings. In other recent developments of EUV optics, large-aperture photon sieves fabricated at NASA-GSFC can provide diffraction-limited imaging at EUV and X-ray wavelengths, and are also being used to provide monochromatic, collimated beams for the calibration of EUNIS and future spectrographs. Recent results will be presented, and capabilities for future missions will be discussed.