Stabilization of a high-order harmonic generation seeded extreme ultraviolet free electron laser by time-synchronization control with electro-optic sampling. (2015)

• Record Type: Journal Article
• Authors: Tomizawa, H.; Sato, T.; Ogawa, K.; Togawa, K.; Tanaka, T.; Hara, T.; Yabashi, M.; Tanaka, H.; Ishikawa, T.; Togashi, T.; Matsubara, S.; Okayasu, Y.; Watanabe, T.; Takahashi, E.J.; Midorikawa, K.; Aoyama, M.; Yamakawa, K.; Owada, S.; Iwasaki, A.; Yamanouchi, K.
• Is Part Of: High power laser science and engineering. Volume 3(2015)
• Publication Date: 2015
• Subjects: arrival-timing monitor, -- electro-optic sampling (EOS), -- high-gain harmonic generation (HGHG), -- high-order harmonic generation (HHG), -- self-amplified spontaneous emission (SASE), -- the soft x-ray water window region, -- wavelength-tunable seeded FEL, -- X-ray free electron laser (XFEL); High power lasers -- Periodicals; 621.366
• DOI: 10.1017/hpl.2015.9
• Languages: English
• ISSNs: 2095-4719

Abstract

Abstract : A fully coherent free electron laser (FEL) seeded with a higher-order harmonic (HH) pulse from high-order harmonic generation (HHG) is successfully operated for a sufficiently prolonged time in pilot user experiments by using a timing drift feedback. For HHG-seeded FELs, the seeding laser pulses have to be synchronized with electron bunches. Despite seeded FELs being non-chaotic light sources in principle, external laser-seeded FELs are often unstable in practice because of a timing jitter and a drift between the seeding laser pulses and the accelerated electron bunches. Accordingly, we constructed a relative arrival-timing monitor based on non-invasive electro-optic sampling (EOS). The EOS monitor made uninterrupted shot-to-shot monitoring possible even during the seeded FEL operation. The EOS system was then used for arrival-timing feedback with an adjustability of 100 fs for continual operation of the HHG-seeded FEL. Using the EOS-based beam drift controlling system, the HHG-seeded FEL was operated over half a day with an effective hit rate of 20%–30%. The output pulse energy was $20~{\rm\mu}\text{J}$ at the 61.2 nm wavelength. Towards seeded FELs in the water window region, we investigated our upgrade plan to seed high-power FELs with HH photon energy of 30–100 eV and lase at shorter wavelengths of up to 2 nm through high-gain harmonic generation (HGHG) at the energy-upgraded SPring-8 Compact SASE Source (SCSS) accelerator. We studied a benefit as well as the feasibility of the next HHG-seeded FEL machine with single-stage HGHG with tunability of a lasing wavelength.