Simultaneous measurement of the fundamental and third harmonic FEL at LEBRA

Lasing of a free electron laser (FEL) at a wavelength of 1.5 µm has been achieved at Laboratory for Electron Beam Research and Application (LEBRA), Nihon University. In order to study its characteristics in detail, a measurement system for the fundamental and the 3rd harmonic radiation was set up. In this system the visible and the infrared light beams are separated from each other using a commercial cold mirror which is a kind of dielectric multi-layer mirrors. The system made it possible to obtain several FEL parameters simultaneously, such as the yield, the beam profile and the spectrum. It will be useful for the investigation into a phenomena that seems to be the non-linear higher harmonics discussed in recent study on the self amplified spontaneous emission.