Focusing of cold neutrons: Performance of a laterally graded and parabolically bent multilayer

We have designed and built a parabolically shaped reflector with a Ni/Ti-multilayer coating, graded along the length of the device. The bilayer thickness follows the varying angle of incidence to match the Bragg condition for a beam parallel to the axis of the parabola. As measurements show, this concept leads to a higher reflectivity for monochromatic neutrons compared to a conventional supermirror coating. With a reflectivity R>96%R>96% we measured a gain of 5 when focusing a 8.6 mm wide beam of 0.1∘0.1∘ divergence down to 1.6 mm. The wavelength band was 4.7ű5% and the focal point was 250 mm behind the device.