Kazuaki Togawa

Extreme ultraviolet free electron laser seeded with high-order harmonic of Ti:sapphire laser

The 13th harmonic of a Ti:sapphire (Ti:S) laser in the plateau region was injected as a seeding source to a 250-MeV free-electron-laser (FEL) amplifier. When the amplification conditions were fulfilled, strong enhancement of the radiation intensity by a factor of 650 was observed. The random and uncontrollable spikes, which appeared in the spectra of the Self-Amplified Spontaneous Emission (SASE) based FEL radiation without the seeding source, were found to be suppressed drastically to form to a narrow-band, single peak profile at 61.2 nm. The properties of the seeded FEL radiation were well reproduced by numerical simulations. We discuss the future precept of the seeded FEL scheme to the shorter wavelength region.

Two-colour hard X-ray free-electron laser with wide tunability

Ultrabrilliant, femtosecond X-ray pulses from X-ray free-electron lasers (XFELs) have promoted the investigation of exotic interactions between intense X-rays and matters, and the observation of minute targets with high spatio-temporal resolution. Although a single X-ray beam has been utilized for these experiments, the use of multiple beams with flexible and optimum beam parameters should drastically enhance the capability and potentiality of XFELs. Here we show a new light source of a two-colour double-pulse (TCDP) XFEL in hard X-rays using variable-gap undulators, which realizes a large and flexible wavelength separation of more than 30% with an ultraprecisely controlled time interval in the attosecond regime. Together with sub-10-fs pulse duration and multi-gigawatt peak powers, the TCDP scheme enables us to elucidate X-ray-induced ultrafast transitions of electronic states and structures, which will significantly contribute to the advancement of ultrafast chemistry, plasma and astronomical physics, and quantum X-ray optics.

A soft X-ray free-electron laser beamline at SACLA: the light source, photon beamline and experimental station

The status of a soft X-ray free-electron laser beamline at SACLA is reported.

Full-coherent free electron laser seeded by 13th- and 15th-order harmonics of near-infrared femtosecond laser pulses

By introducing 13th- (61.7?nm) and 15th-order harmonics (53.4?nm) of femtosecond laser pulses at 800?nm into an undulator of SCSS (SPring-8 Compact SASE Source) test accelerator at RIKEN, these harmonic pulses were amplified by a factor of more than 102?with a high contrast ratio through the interaction between accelerated electron bunches and the harmonic pulses. From numerical simulations of the amplification processes of high-order harmonic pulses in the undulator, optimum conditions of the electron bunch duration interacting with the high-order harmonic pulses were investigated for generating full-coherent and intense pulses in the extreme ultraviolet wavelength region.

Current status of the EUV/soft x-ray FEL beamline at SACLA(Conference Presentation)

SACLA was inaugurated in March 2012 with two beamlines: BL3 for hard X-ray FEL and BL1 for wide range spontaneous emission. Currently, all user experiments have been performed at BL3 and BL2 that was constructed as the second hard XFEL beamline. To enhance research opportunities with softer X-ray FEL, we decided to relocate the SCSS test accelerator, which was a prototype of SACLA and decommissioned in 2013, to the SACLA undulator hall, to connect to BL1, and to generate EUV and soft X-ray FEL independently of the SACLA linac. In addition, we started commissioning of the upgraded BL1 in September 2015, and successfully observe SASE lasing at a photon energy of 36 eV in October. We are now constructing the end station, and will start commissioning in June 2016. We will install two C-band accelerator units that increase an electron beam energy up to 750 MeV with a photon energy up to 100 eV in the summer of 2016. In this presentation, I will report the latest status of the beamline.

Extreme ultraviolet free electron laser seeded by high-order harmonic

We first generated seeded FEL radiation in the EUV region at 61.2 nm with the 13th harmonic of a Ti:sapphire laser. We observed single-peak spectra with drastic enhancements of intensity by nearly three-orders of magnitude.