Coherent Harmonic Generation experiments on UVSOR-II storage ring

In this paper, generation of the second, third and fourth harmonics of the fundamental (400, 266 and 200 nm) using planar undulators is reported, together with angular distribution measurement of the second harmonic. We also present coherent generation of the second and third harmonic using helical undulators. These investigations on even harmonic generation with both undulator configurations may provide interesting insight in nonlinear harmonic generation with FELs for next generation FELs, aiming at GW pulse delivery at sub-nm wavelengths.