Development of figure correction system for inner surface of ellipsoidal mirrors

Abstract X-ray mirrors are widely used in advanced x-ray facilities. An ellipsoidal mirror is used in soft x-ray focusing optics. To prevent a decrease in the intensity density or distortion of the wavefront of reflected x-ray beams, the inner surface of an ellipsoidal mirror should have high precision. Differential deposition is a method of fabricating a shape on a mirror surface. However, mirrors with a small diameter cannot be corrected by the conventional process. In this study, a figure correction method employing ion beam sputtering deposition was developed. The sputtering target is placed inside the ellipsoidal mirror. Then, a cylindrical tube with a small aperture is inserted inside the mirror to realize selective deposition. The figure accuracy of an ellipsoidal mirror is improved even when its diameter is less than 10 mm. This figure correction system can also be applied to various axisymmetric devices with a small diameter.