Resolution performance of extreme ultraviolet telescope

Extreme Ultraviolet Telescope (EUT) will image solar corona in four EUV narrow bandpasses defined by multilayered coatings deposited on normal incidence optics. In order to make sure it will get sub-arcsecond angular resolution in the mission we have to test its resolution performance on ground. The EUT is aligned by Zygo interferometer first and a global wavefront error of 0.152 λ peak to valley is obtained (λ = 632.8nm ). Because of the difficulty of angular resolution test for EUT at its operating wavelengths, we test its optical performance at visible and UV band. The method is to place the resolution test-target on the focal plane of collimator and illuminate the target by visible and UV light respectively, then the collimated light will go through EUT and image at focal plane on CCD. By analysis of the images obtained in experiments we conclude that the angular resolution of EUT is 1.22" at visible light (λ = 570nm ) which is very close to diffraction limit (1.20") and according to these results we estimate that the operational wavelength resolution is better than 0.32", meets design requirements. While for UV light, the angular resolution is 1.53" that is different from diffraction limit (0.53"), the error comes mainly from large pixel of EUV camera.