Wavefront measurement of x-ray laser nanobeam using phase diffraction grating

Recently, use of a focusing system for X-ray free electron laser (XFEL) has been promoted. We have proposed wavefront measurement by the single-grating interferometer using Talbot effect. It enables us to examine figure errors on a focusing mirror and detect alignment errors of a focusing system. Using this method, we performed wavefront measurement of 50-nm focused beam with the Fourier transform method and the fringe scan method. As a result, we confirmed it could measure wavefront aberration with a high accuracy. We plan that this method can be applied to adjustment of a focusing system. (author)