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A project is underway that aims to generate attosecond pulses via high-harmonic generation in rare gases, driven by extremely short and highly intense pulses from free-electron-laser oscillators. For this purpose, it has been planned that a new photocathode RF gun, dedicated to high-bunch-charge operation, will be installed at the KU-FEL (Kyoto University Free Electron Laser) oscillator facility. In this study, RF guns with two different structures (1.6-cell and 1.4-cell) were compared, from the perspective of exploring the possibility of introducing bunch-interval modulation, which is important for achieving high extraction efficiency in the FEL oscillator. As a result, it was confirmed that the introduction of bunch-phase modulation would be possible only in the case of the 1.6-cell RF gun. After the structure of the RF gun was decided on, particle-tracking simulations were performed, to study the electron-beam parameters using the 1.6-cell RF gun and 1 nC bunch charge. The results showed that we could obtain the peak current of 1 kA without a large degradation of the other parameters.

Two-photon selective excitation of an infrared (IR)-inactive phonon mode by a mid-infrared tunable free-electron laser (FEL) was accomplished. The mode-selective phonon excitation of IR-active mode by one-photon excitation using FEL (Yoshida et al. (2013) [20]) was extended to the IR-inactive mode excitation. The T2g optical phonon mode in single-crystal diamond at 1, 332cm−1 was selected, and the FEL photon energy corresponding to the oscillation wavelength was tuned to the half of the target phonon energy. The successful mode excitation was confirmed by anti-Stokes Raman scattering signal of T2g for the sample at cryogenic temperature, where all other modes were suppressed. The signal was observed at T2g phonon energy with red-shift of the peak to 1, 306cm−1, which was accompanied by surface damage induced by intense laser irradiations.

Computed Tomography (CT) using X-ray attenuation by atomic effects is now widely used for medical diagnosis and industrial non-destructive inspection. In this study, we performed a tomographic imaging of isotope (²⁰⁸Pb) distribution by the Nuclear Resonance Fluorescence (NRF), i.e. isotope specific resonant absorption and scattering of gamma rays, using Laser Compton Scattering (LCS) gamma rays. The NRF-CT image which includes both effects of atomic attenuation and nuclear resonant attenuation was obtained. By accounting for the atomic attenuation measured by a conventional method at the same time, a clear ²⁰⁸Pb isotope CT image was obtained. The contrast degradation due to notch refilling caused by small-angle Compton scattering is discussed. This study clearly demonstrates the capability of the isotope-specific CT imaging based on nuclear resonant attenuation which will be a realistic technique when the next generation of extremely intense LCS gamma-ray sources will be available. The expected image acquisition time using these intense LCS gamma rays was discussed.

Degradative solvent extraction (DSE) is effective in both dewatering and upgrading biomass wastes through the selective removal of oxygen functional groups. However, this conversion mechanism has yet to be elucidated. Here, liquid membrane-FTIR spectroscopy was utilized to examine the main liquid product (Solvent-soluble) without sample modification. Rice straw (RS) and 1-methylnaphthalene (as a non-hydrogen donor solvent) were used as materials, and measurements were performed at treatment temperatures of 200, 250, 300, and 350 °C for 0 min, and at 350 °C for 60 min. The Solvent-soluble spectra were quantitatively analyzed, and changes in the oxygen-containing functional groups and hydrogen bonds at each temperature were used to characterize the DSE mechanism. It was determined that the DSE reaction process can be divided into three stages. During the first stage, 200–300 °C (0 min), oxygen was removed via dehydration, and aromaticity was observed. In the second stage, 300–350 °C (0 min), deoxygenation reactions involving dehydration and decarboxylation were followed by reactions for aromatization. For the third stage, 350 °C (0–60 min), further aromatization and dehydration reactions were observed. Intramolecular reactions are indicated as the predominant mechanism for dehydration in RS DSE, and the final product is composed of smaller molecular compounds.

The single-phonon mode was selectively excited in a solid-state sample. A mid-infrared free-electron laser, which was tuned to the target phonon mode, was irradiated onto a crystal cooled to a cryogenic temperature, where modes other than the intended excitation were suppressed. An A 1(LO) vibrational mode excitation on GaN(0001) face was demonstrated. Anti-Stokes Raman scattering was used to observe the excited vibrational mode, and the appearance and disappearance of the scattering band at the target wavenumber were confirmed to correspond to on and off switching of the pump free-electron laser and were fixed to the sample vibrational mode. The sum-frequency generation signals of the pump and probe lasers overlapped the Raman signals and followed the wavenumber shift of the pump laser.

Some of the vibrational modes of crystalline organic polymers are known to be sensitive to the structural change from the crystalline phase to the amorphous phase, and vice versa. Using a mid-infrared (mid-IR) pulse from a free-electron laser as a probe, we demonstrate the time-resolved detection of structural change in crystalline polymer (polyethylene) films upon laser heating by a Q-switched Nd:YAG laser. Transmittance of the resonant mid-IR pulse almost instantaneously changes before and after the Nd:YAG laser pulse if its fluence is sufficient to induce the structural change in the film. The developed technique would be useful to study the time-dependent dynamics of the structural change in various materials.

Modifying the electronic structure may allow a bulk material to efficiently absorb radiation as well as excite and emit atomic plasma. The interaction between microwaves and metal oxides is investigated by analyzing the electronic structure of ZnO with and without microwave (MW) irradiation using absorption, photoluminescence (PL), and PL excitation (PLE) spectroscopies and utilizing an ultraviolet synchrotron light source. MW irradiation lowers the energy of the absorption edge of ZnO producing defects. Additionally, MW irradiation causes a resonantly enhanced change in the intensity and peak shift of the PL band. These phenomena indicate that the defects generated by MW irradiation change the electronic structure of ZnO and the electron transition process.

Coherent control of a lattice vibration in bulk solid (mode-selective phonon excitation: MSPE) is one of the attractive methods in the solid state physics because it becomes a powerful tool for the study of ultrafast lattice dynamics (e.g. electron-phonon interaction and phonon-phonon interaction). Not only for that, MSPE can control electronic, magnetic, and structural phases of materials. In 2013, we have directly demonstrated MSPE of a bulk material with MIR-FEL (KU-FEL) by anti-Stokes Raman scattering spectroscopy. For the next step, we are starting a phonon dynamics measurement to investigate the difference of physical property between thermally excited phonon (phonon of equilibrium state) and optically excited phonon (phonon of non-equilibrium state) by time-resolved method in combination with a pico-second VIS laser. By using pico-second laser, we also expect to perform the anti-Stokes hyper-Raman scattering spectroscopy to extend MSPE method to the phonon mode which has Raman inactive . As the first step, we have commissioned the time-resolved phonon measurement system and started measurement on 6H-SiC. In this conference, we will present the outline of measurement system, and experimental results.

To realize a short-period strong-field undulator, we proposed a high temperature superconducting bulk staggered array undulator (Bulk HTSC SAU) and proceeded proof of principle experiments and numerical studies. We have succeeded to generate periodic transverse magnetic fields whose strength was controlled by an external solenoid field. At the same time, we revealed a problem; at both ends of undulator, field distribution is substantially distorted. We proposed several approaches of field correction. To verify the effectiveness of these field correction methods, it is necessary to measure the magnetic field distribution precisely, not only inside of the undulator but also both ends. For this purpose, we developed a rotary measurement system to measure the magnetic field distribution at the end of the undulator. Multiple Hall sensors are placed on a circuit board at equal intervals from the centre of the board. By rotating and moving the board, the probe can measure axial field in 3D space on the undulator ends. In this paper, we deliver specifics of the system.

Simple, compact, and powerful seeded terahertz-free electron laser (THz-FEL) which consists of a photocathode radio-frequency gun, a focusing solenoid, an undulator and a THz wave parametric generator has been designed. A start-to-end calculation has been performed by using the particle tracking code PARMELA and the FEL gain simulation code GENESIS1.3. To obtain a higher FEL gain, we searched a better condition of the electron beam parameter and the seed light. In the present design scheme, the FEL peak power was calculated to be 3 kW at the FEL resonant wavelength of 179 m. Since the power of the seed light was 0.20 W, the light power was amplified almost 10⁴ times.