Detection of coherent transition radiation and its application in beam diagnostics and particle identification

The first observation of the angular distribution of coherent (resonant) transition radiation at soft-X-ray photon energies (1 to 3 keV) is reported. Two different radiators were constructed, each consisting of stack of eight foils of 3.5- mu m-thick mylar. One of the radiators was designed to demonstrate interfoil coherence and had foil-to-foil spacing of 8.5 mu m throughout the stack. The other radiator had large random spacings that prevented coherent interference between foils. These radiators were irradiated with electron beams with energies ranging from 63 to 97 MeV, and their angular distributions were compared. The distributions were symmetrical around the axis of the transition-radiation cone. For the coherent case the angle of peak photon emission was found to increase with increasing electron-beam energy; for the incoherent case the angle was found to decrease with increasing electron energy. The coherent case is contrary to the normally expected behavior and can be used as the basis of an electron beam-energy diagnostic.<>