Coherent diffraction radiation interferometry and short bunch length measurements

The promising approach to measure a length of subpicosecond electron bunch is connected with measurements of coherent diffraction radiation (CDR) spectra due to strong dependence of the spectrum shape on the bunch length σ_z in the wavelength region λ ∼ σ_z [Proceedings of the International Symposium on New Visions in Laser-Beam Interactions, Nucl. Instr. and Meth. A 455 (1) (2000)]. The spectral measurements may be carried out by using an interferometer or a polychromator. The alternative approach for similar measurements is proposed in the paper. The interference pattern from two shifted halves of a CDR target may be used for this aim. If the broadband detector measures a CDR yield around λ₀ ∼ σ_z then moving one half of the CDR target relative to other (parallel to beam) in the range of a few bunch lengths one can obtain the detuning curve (interferogram). The shape of detuning curve and its connection with bunch length is calculated for different detector apertures and detector waveband. The proposed technique may open the new possibility for non-invasive bunch length measurements in the subpico-second range.