Measurements of the pulse length of the FEL nonlinear harmonics radiation

The pulse length of the fundamental and the nonlinear harmonics of the FEL generated at LEBRA have been measured simultaneously by means of Michelson interferometer. The nonlinear harmonics is thought of as the coherent radiation emitted from the micro-bunches corresponds to each harmonics formed by the fundamental radiation. In this measurement, the wavelength of the fundamental radiation is 1500 nm, then, the wavelength of the second and third harmonics are 750 nm and 500 nm respectively. The fundamental radiation is detected by using InGaAs photodiode and the second and third harmonics are detected by using Si photodiode. Measured pulse length of the fundamental radiation is about 65 μm and the second and the third harmonics is about 35 μm and 43μm of FWHM. (author)