Yuji Otake

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.

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.

Seismometer using a vertical long natural-period rotational pendulum with magnetic levitation

We have demonstrated a highly sensitive/wideband vertical-component seismometer using an astatic rotational pendulum to obtain a long natural period. This seismometer employs magnetic levitation for removing any parasitic resonances of a spring to support a weight due to gravity and the thermal dependence of the spring constant. The pendulum has a cylindrical plunger-type permanent magnet that has a weight at one side of its end edge. The plunger magnet is inserted into a uniform magnetic field generated by a window-frame-type permanent magnet, and attached to two crossed-leaf spring hinges as a rotational axis outside of the bore of the magnet. Magnetic forces applied to the plunger magnet counterbalance the gravitational force at the weight. To realize stable operation of the rotational pendulum without any unnecessary movements of the plunger magnet, a tilt of lines of the magnetic force in the bore of the window-frame magnet was compensated by a tilted magnetic-pole surface near to its opening. The fi...

Development of a horizontal component seismometer using a magnetic spring

Discoveries in seismology depend on seismological-observationalnetworks using highly sensitive/broadband seismometers, such as the STS-I. A pendulum with a long natural period is directly associated with the high sensitivity and wideband characteristics of these seismometers. The aim of this study on a vibration detector is to realize a seismometer with a sensitivity of less than several tens of microgal and a natural period of more than 100 s, which would surpass those of the STS-I. A new principle for a vibration detector, rather than a mechanical spring, which traditional seismometers use, is needed to avoid any spring-constant drift that depends on the temperature and the elastic deformation. The principle is a magnetic spring using the interaction force between a magnetic field and a permanent magnet. The magnet, which is inserted into the inner bore of a solenoid coil, behaves like a pendulum with a magnetic restoring force. The detector comprises a cylindrically shaped permanent magnet, a solenoid coil, a position detector, and a weight with a levitation system. This detector for horizontal components, which can achieve a natural period of more than several hundred seconds, has been theoretically shown by a calculation using parameters that would be possible with commercial parts. A detector using pneumatic levitation was recently tested. The results of the test showed that the natural period could reach more than 27 s without a position-feedback control system for the weight. The basic principle of the magnetic spring, that acts as a mechanical pendulum, was proved by this test. The detector showed the possibility of realizing a long natural period of more than 100 s with a position-feedback control system for the weight.

Full-coherent HHG-seeded EUV-FEL locked by EOS timing feedback

We are developing seeded XFEL pulse with HH for coherent XFEL pulse. Using the monitor of temporal overlap with EO sampling technique, seeded pulse was obtained long time against timing drift.

A few tens of microjoule full-coherent EUV-FEL seeded by high-order harmonic beam

Output energy exceeding 20 μJ has been achieved in the EUV region at 61 nm by the harmonic seeded FEL scheme. Event ratio of the seeded FEL operation has been dramatically improved by a feedback system with an electro-optic sampling technique.

Enormous Amplification of Full-Coherent Radiation in the Extreme Ultraviolet Region with a Free-Electron Laser

High-order harmonic beam was injected as a seeding source to a 250-MeV free-electron-laser amplifier. When the amplification conditions were satisfied, strong enhancement of the radiation intensity by a factor of 650 was observed at a wavelength of 61.5 nm. The random and uncontrollable spikes, which appeared in the spectra of the Self-Amplified Spontaneous Emission based FEL radiation without the seeding pulse, were found to be suppressed drastically to form to a narrow-band, single peak profile at the seeding wavelength. The properties of the seeded FEL radiation were well reproduced by numerical simulations.

Seeding of extreme ultraviolet free electron laser with high-order harmonic

Frontiers in optical science in the short-wavelength region have greatly been expanded by the advent of intense, single-pass free-electron lasers (FELs) based on a self-amplified spontaneous emission (SASE) scheme [1,2]. However, their temporal profile and frequency-domain spectra are composed of random and uncontrollable spikes, exhibiting shot-to-shot fluctuation originating from the stochastic start-up process intrinsic to spontaneous radiation. The most straightforward method for improving the temporal coherence of FEL is to inject the high-order harmonic (HH) generated by a laser into an FEL amplifier. In this paper, we first demonstrate [3] the 13th harmonic (61 nm) [4] of a Ti:Sapphire laser in the plateau region was injected as the SPring-8 Compact SASE Source test accelerator [2].

EUV-FEL seeded by high-order harmonic

We first demonstrated a seeded FEL radiation in the EUV region at 61.2 nm with the 13th high-order harmonic beam. We observed single-peak spectra with drastic enhancements of intensity by nearly three-orders of magnitude.