Electron-beam diagnosis with Youngʹs interferometer in soft X-ray region

We report an emittance measurement with undulator radiation performed at BL-16B of the Photon Factory, KEK. The spatial coherence (visibility) and the beam size of undulator radiation are measured with a Youngʹs interferometer and a wire scanner in the soft X-ray region, of about 40–200 eV. The horizontal emittance is estimated as around 40 nm rad, which is consistent with the design value 36 nm rad. The vertical emittance is estimated as larger than 1.5 nm rad. This value is too large if the coupling is assumed to be 2%. The discrepancy in the vertical direction is due to an incomplete adjustment of the direction of a double slit and phase randomization by a dirty grating in the Youngʹs interferometer.