A capacitance-based micropositioning system for x-ray rocking curve measurements

Certain types of x-ray experiments require very precise angular positioning of crystals in the vicinity of the Bragg reflection condition. A system applicable to some measurement of this type is described which achieves a long-term angular stability of approximately 10(-7) radians, coupled with a linear angular readout. This is achieved through a novel capacitance sensing system which provides angle measurement, together with the use of an auxilliary servo loop based on the Bragg condition to ensure long-term overall angular stability.