Full Surface Testing of Grazing Incidence Mirrors

The objective of the Phase-II research was to design, construct and test a prototype interferometer system FSIS for the purpose of testing cylindrical-like mirrors such as those used in grazing incidence X-ray imaging applications. Existing instruments are based on a shearing interferometry, dual laser beam scanning approach, measuring the slope or curvature functions along a single long trace in the long direction of the cylindrical mirror. While these instruments are characterized by a high measuring accuracy, they are very slow and environmentally sensitive. An even slower and more complex two-dimensional scan must be implemented if the full surface measurement is required. Our approach is also based on interferometric slope measurement in the direction of the long side of the mirror, using a grating shearing interferometer head. A full-width beam covering an extended subaperture of the mirror is canned in discrete steps in the direction of the long side of the mirror, so that a single scan allows coverage of the whole mirror surface. By least square fitting the series of subaperture measurements, the system yields parallel measurement of a multiplicity of long traces in the direction of scan.