Effects of diffraction and target finite size on coherent transition radiation spectra in bunch length measurements

Effects of diffraction and the size of the target on TR in the context of CTR-based bunch length measurements are studied on the basis of Kirchoff diffraction theory. Spectra of TR from the finite-size target for several schemes of measurements are calculated in the far-infrared region showing strong distortion at low frequencies. Influence of the effect on the accuracy of bunch length measurements is estimated.