Temporal overlapping for HHG seeded EUV-FEL operation by using EOS-based timing-drift controlling system

Free-electron lasers (FELs), which are based on a self-amplified spontaneous emission (SASE) scheme, have attractive characters as the intense light source in short-wavelength region. However, their temporal profile and frequency-domain spectra have shot-to-shot fluctuating spikes originated from the SASE process. One of the promising approaches to these problems is a seeded FEL scheme, which is possible to realize full-coherent light pulses without shot-noise structures. We already reported the higher-order harmonic (HH) seeded FEL operation at the fundamental wavelength of 61.2 nm using a seeding source of a HH pulses from Ti:sapphire laser at the SPring-8 Compact SASE Source (SCSS) test accelerator. However, the seeded FEL pulses (intensity >4σ of SASE) were only obtained 0.3% in 3000 shots.