Design of solar extreme ultraviolet slitless imaging spectrometer based on flat-field holographic concave grating

Performances of a novel solar extreme ultraviolet (EUV) slitless imaging spectrometer in a stigmatic design are presented with an aberration-correcting flat-field holographic concave grating (HCG). The instrument is based on a conventional off-axis Maksutov telescope with aberration-corrected holographic rulings on the secondary optic. These rulings with varied line-space enable stigmatic imaging in diffracted light with a minimum number of optical elements, thereby maintaining a high system efficiency. The novel design has improved temporal resolution prominently by throwing away the slit and no scanning, either spatially or spectrally, permitting EUV spectroscopy with a high time cadence in observation of the full solar disk. In this approach all data are taken simultaneously over the whole field of view, and hence no confusion of temporal evolution with spatial or spectral variation. ZEMAX software is used to obtain the final parameters of spectrometer through global optimization and multiple configuration. The slitless imaging spectrometer possesses imaging detectors at three orders of flat-field HCG, which provides cotemporal imaging and spectroscopy with high spatial resolving element (1.8arcsec/pixel) and spectral resolving element (60mÅ/pixel) for a narrowband at 304 Å and a wide field of view (36arcmin). The performance of the resulting optical design are evaluated, and the imaging quality obtained here is excellent which can be inferred from the root-mean-square spot diagram.