Performance Of High Spatial Frequency X-Ray Transmission Gratings

We examine the performance of high spatial frequency "phased" X-ray transmission gratings developed for the High Energy Transmission Grating Spectrometer on the Advanced X-ray Astrophysics Facility (AXAF). The gratings tested here nominally consist of 1 thick gold lines of 0.2 μm period covering approximately 5 cm 2 of a polyimide membrane. A table-top setup at MIT employs the gratings in reflection to diffract UV (325 nm) laser light. It is used to measure grating periods and indicates that period variations within and between gratings are a few parts in 104. Tests performed at the Marshall Space Flight Center 304 m X-ray Facility using 1.5 keV (Al Ka) X-rays in transmission corroborate the UV measurements and demonstrate geometrically-limited resolving powers of E/ΔE-750. Finally, X-ray transmission tests performed in the MIT 25 m X-ray facility provide measurements of period, line thickness, space-to-period ratio, tilt of grating lines, and efficiency. We find that the agreement between the design parameters and the measured parameters is good.