Application limit of SR interferometer for emittance measurement

We investigate the application limit of the SR interferometer for emittance measurement at the KEK-ATF. We need to consider two important problems, which are the limitation of the availability of the van Cittert-Zernike theorem and the diffraction effect due to a narrow vertical aperture of the SR extraction line. The former problem is analyzed with the theory introduced in another paper. The latter one is studied with a numerical calculation, where the narrow aperture is assumed to be an optical slit with an adequate vertical width. We show that these problems must be solved for the accurate measurement of electron emittance, especially in the vertical direction