X-ray resolution tests of an off-plane reflection grating for IXO

We describe the experimental apparatus in use to test an off-plane reflection grating for the soft x-ray (0.3-1.0 keV) bandpass. The grating is a prototype for the X-ray Grating Spectrometer on the International X-ray Observatory (IXO). It has holographically-ruled radial grooves to match the converging beam of a 6.5 m focal length telescope. Laboratory tests are ongoing, with ray tracing indicating that a resolution (ΔE/E) >3,000 is achievable across the 0.3-1.0 keV bandpass- the requirement to achieve IXO science goals.