The joint astrophysical plasmadynamic experiment (J-PEX) high-resolution EUV spectrometer: diffraction grating efficiency

We have fabricated five new holographic ion-etched polymer-coated gratings for a reflight on a sounding rocket of the J-PEX high-resolution EUV spectrometer. The gratings are parabolic (nominal 2000-mm focal length), large (160 mm x 90 mm), and have a blazed groove profile of high density (3600 grooves/mm at the vertex). They have been coated with a high-reflectance multilayer of Mo/Si/C. Using an atomic force microscope, we examined grating topography before multilayer coating. The surface roughness is 2 angstrom rms and the blaze angle is near the target value of 2.40. Using synchrotron radiation, we completed an efficiency calibration map of each. multilayer-coated grating over the wavelength range 220-245 angstrom. At an angle of incidence of 50, the average efficiency in the first inside order peaks near 234 A. The average peak efficiency is 12.3 +/- 1.0% for Grating 1, 12.6 +/- 2.4% for Grating 2, 12.6 +/- 1.8% for Grating 3, 14.1 +/- 3.0% for Grating 4, and 13.0 +/- 1.0% for Grating 5. The derived groove efficiency averaged over all gratings is approximately 50%, which meets our goals. Refined models of the multilayer gratings are required to resolve remaining issues.