A Bright Source Defocusing Optic for IXO

The very large collecting area of the International X-ray Observatory, 3 m² at 1 keV, has the potential to provide a unique science capability of very high time resolution combined with high spectral resolution on bright X-ray sources. However, this will only be possible if the X-ray detectors can meet the count rate demands and this is difficult if not impossible with the expected angular resolution of 5 arc seconds. Using a square pore Micro Channel Plate as a defocusing optic the point spread function of a source on axis can be defocused so that it covers many pixels in the focal plane and then the X-ray detectors can cope with a much higher count rate, possibly 100-1000 times larger. We pesent a design, implementation and predicted performance of such an optic and discuss the science which can be achieved using it.