Surface roughness effects on cylindrical grazing incidence x-ray optics for transition radiation

Quartz and nickel cylinders were used as grazing incidence x-ray optics for transition radiation (TR) from Al, Ti, and Cu foil stacks. The cylinders were used to direct the otherwise diverging TR to a small spot (1 mm diameter), with measured fluxes of up to 330 W/A cm2 averaged over the spot area. Computer simulations were performed and compared to the measured results. It was found that including surface roughness effects in the form of a Debye–Waller reduction factor on the reflectivity was necessary to get good agreement between the simulations and experimental results in certain cases, but not in others. A simple heuristic model which can be used to determine when roughness effects are important is presented. Use of this model in conjunction with the computer simulations accurately predicts the measured results, and further suggests the use of different optic materials at different x-ray wavelengths.