VUV seeded FEL experiment at the SCSS test accelerator

A short wavelength seeded FEL has been demonstrated at the SCSS test accelerator using high-order harmonics generated in gas of a titanium-sapphire laser as an external seed source. After the improvement of the accelerator stability and undulator magnetic errors in 2007, the FEL gain was drastically increased and detailed measurements have been carried out particularly on the spectral characteristics of the seeded FEL. Although the wavelength of the seed is 160 nm for the moment, we have succeeded to observe nonlinear harmonics of the FEL fundamental wavelength including both odd and even harmonics. It leads to the development of a short wavelength seeded FEL. Currently we are working on the modification of the seeding system in order to reach a 50-60 nm range using high-order harmonics of the plateau region. By combining a short wavelength seed with nonlinear harmonics, a seeded FEL below 10 nm becomes feasible.