Measurement of the coherent radiation from the electron beams used for the FEL experiments at Osaka University

A study was made for the coherent radiation from the multibunch electron beam used for the FEL oscillation experiments at Osaka University. The spectrum of the coherent synchrotron radiation from the beam was measured at wavelengths of 1–2 mm. At 1 mm the intensity of radiation is 6×105 times that of the incoherent radiation. The intensity nearly agreed with that obtained by calculation for the triangular shape of the bunch. The intensity of spontaneous emission at a wavelength of 40 μm from the multibunch beam passing through a wiggler was also measured. For the charge of electrons in a bunch above 0.39 nC the radiation was enhanced from the incoherent spontaneous emission. The intensity in the enhanced part was approximately proportional to the square of the charge per bunch, which was attributed to the coherence effects.