Diffraction radiation from a charged particle moving through a rectangular hole in a rectangular screen

We developed a new model for calculating diffraction radiation (DR) from an electron moving through a rectangular hole in a rectangular screen. The calculations show that short wavelength DR is very sensitive to the beam size. For example, optical DR (ODR) could be used to measure the beam size as small as 10 μm. Moreover, splitting two polarization components it becomes possible to measure vertical and horizontal beam sizes independently. We have calculated the DR spectra and compared them with TR ones for a finite size target. It is shown that when the DR wavelength is comparable with or longer than the hole size, the photon yield is mostly determined by the outer target dimensions. It means that in case transversal beam dimensions smaller than the observation wavelength the coherent DR could be used for non-invasive bunch length measurements with the same accuracy as the coherent TR techniques. However, the outer target dimensions must be taken into account because the finite target size causes a significant intensity suppression in the long wavelength spectral range as well as distortion of the coherent spectrum.