Optical Diffraction Radiation from a beam off a circular target
  We calculate the optical diffraction radiation generated by a bunch of high energy particles as they pass through a round hole within an annular metallic ring. We derive expressions for the differential angular spectrum in the far-field and the intensities of the horizontal and vertical polarizations. The sensitivity of the spectrum to changes in beam size and position is shown. The total photon yield from the bunch is calculated and used to set limits on the detectable wavelengths. 
Tanaji Sen