Beam characterization of mid-infrared free electron laser to drive high-harmonic generation

The maximum energy of photons from high-harmonic generation (HHG) increases with the wavelength of the driving laser. A free electron laser (FEL) is a continuously tunable light source in the mid-infrared wavelength range and it is useful for investigating the extension of the accessible photon energy in HHG. Recently, the undulator magnets of the infrared FEL at the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University, have been replaced, and then the output power of the FEL has increased. Here, we evaluate the pulse duration and focal beam size of the FEL and show that the LEBRA FEL with 2-μm and 3-μm laser wavelengths under a 44-MHz bunch repetition mode can drive HHG.