Detection of optical transition radiation and its application to beam diagnostics

Optical transition radiation produced by 40-60 MeV electrons crossing thin metallic foils has been studied in order to provide a beam diagnostic device. The radiation yield is roughly one photon per 100 electrons and the intensity appears to be Z independent ; the influence of bremsstrahlung is then fairly weak. Measurements of angular and γ dependence, spectral density and polarisation have been carried out and results are in good agreement with theories. When multiple scattering angles are negligible (< γ-1), a strong eneray dependence, close to γ3 , of the light intensity radiated into small solid angles is found. Moreover, the radiation is peaked in a direction making an angle γ-1 with the beam axis. Suitable optical arrangement make it possible beam position and profile determination. Measurement of the polarisation plane rotation by means of a scanning mirror provides a method of determining the incident angle of the beam onto the target. This device looks promising for diagnostics on particle beams-electrons as well as protons-with normalized energies γ in the range 1-103.