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A mid-infrared free-electron laser (MIR-FEL) is a synchrotron-radiation-based femto- to pico-second pulse laser. It has unique characteristics such as variable wavelengths in the infrared region and an intense pulse energy. So far, MIR-FELs have been utilized to perform multi-photon absorption reactions against various gas molecules and protein aggregates in physical chemistry and biomedical fields. However, the applicability of MIR-FELs for the structural analysis of solid materials is not well recognized in the analytical field. In the current study, an MIR-FEL is applied for the first time to analyse the internal structure of biological materials by using fossilized inks from cephalopods as the model sample. Two kinds of fossilized inks that were collected from different strata were irradiated at the dry state by tuning the oscillation wavelengths of the MIR-FEL to the phosphoryl stretching mode of hydroxyapatite (9.6 µm) and to the carbonyl stretching mode of melanin (5.8 µm), and the subsequent structural changes in those materials were observed by using infrared microscopy and far-infrared spectroscopy. The structural variation of these biological fossils is discussed based on the infrared-absorption spectral changes that were enhanced by the MIR-FEL irradiation, and the potential use of MIR-FELs for the structural evaluation of biomaterials is suggested.

The isotope selectivity of computed tomography (CT) imaging based on nuclear resonance fluorescence (NRF) transmission method using a quasi-monochromatic laser Compton scattering (LCS) gamma-ray beam in the MeV region was demonstrated at the Ultra Violet Synchrotron Orbital Radiation–III (UVSOR-III) Synchrotron Radiation Facility (Institute of Molecular Science, National Institute of Natural Science) for two enriched lead isotope rods (206Pb and 208Pb) implanted in an aluminum cylinder. Since these two rods show the same gamma-ray attenuation in atomic processes, it is impossible to differentiate between them using a standard Gamma-CT technique based on atomic attenuation of gamma rays. The LCS gamma-ray beam had a maximum energy of 5.528 MeV and an intensity of approximately 5.5 photons/s/eV at the resonance energy ( $J^{\pi } = 1^{-}$ at 5.512 MeV in 208Pb). A lead collimator with a hole diameter of 1 mm was used to define the size of the LCS gamma-ray beam at the CT target. The CT image of the 208Pb rod was selectively obtained with a 2-mm pixel size resolution, which was determined by the horizontal step size of the CT stage.

We introduce a green approach to obtain glucose and low-molecular-weight saccharides directly from the cellulose aggregate by using near- and mid-infrared free electron lasers (IR-FELs). The IR-FEL...

A mid-infrared Free Electron Laser (MIR-FEL) is a candidate to realize a high-repetition-rate atto-second hard X-ray source based on the high harmonic generation (HHG). A new project to conduct a proof of principle experiment of HHG driven by a MIR-FEL has been started since 2018. For this purpose, upgrade project of MIR-FEL at Kyoto University (KU-FEL) has been started to achieve high peak power and ultrashort pulse operation. As the first step of the upgrade, a photocathode drive laser was improved to enable long macro-pulse photocathode operation. The results of the long macro-pulse photocathode operation of KU-FEL will be presented.

Terahertz parametric oscillator (TPO) is one of the attractive ways to generate THz waves. In this study, we proposed a novel high-conversion-efficiency TPO, which is called as synchronously pumped Terahertz parametric oscillator (sp- TPO) by using a pico-second mode-locked laser pulses as a pump beam. An sp- TPO has been designed and constructied. The system performance was measured. As a result, the conversion efficiency from NIR to THz of 2.4 × 10–5 has been achieved. The maximum micro-pulse energy and the peak power were 1.5 nJ and 200 W, respectively. The spectrum and pulse duration measurements by using a Michelson interferometer are under preparation.

We proposed an isotope-selective computed tomography (CT) imaging based on the Nuclear Resonance Fluorescence (NRF) transmission method using a quasi-monochromatic laser Compton scattering (LCS) gamma-ray beam in the MeV region for nuclear safety applications. As the first step, a two-dimensional (2D) NRF-CT image of 208Pb isotope distribution was selectively obtained for the sample target containing two enriched lead isotope rods (206Pb and 208Pb). We are planning to perform an experiment to obtain a three-dimensional NRF Computed Tomography (3D NRF-CT) image for the specific isotope. An automatic measurement system has been developed. As the result, we obtained an excellent quality of 3D gamma-ray CT image.

Light perception is an intriguing subject, and it has been demonstrated that some animals can perceive wavelengths beyond human vision. However, it is still controversial whether animals can see mid-infrared radiation. A combination of two free-electron laser (FEL) facilities, LEBRA-FEL (Nihon University) and KU-FEL (Kyoto University), can provide light sources with high peak power and spatially coherent monochromatic wavelengths that are continuously tuneable from 400 nm to 20 μm. We show that the crayfish (Procambarus clarkii) compound eye responds to pulsed mid-infrared FELs (1 Hz for KU-FEL; 2 Hz for LEBRA-FEL) from 3 to 17 μm. Our finding provides insight into the animal’s visual sensing of mid-infrared radiation, and that the sensing does not depend on thermal effects. Although the behavioural reason for vision in this wavelength range and the mechanism are still under investigation, understanding this type of visual sensing may lead to applications other than photophysical applications.

We developed the isotope-specific Computed Tomography imaging technique based on the Nuclear Resonance Fluorescence absorption method at BL1U of UVSOR-III by using high flux and quasi-monochromatic gamma-ray beam for a sample target containing two enriched lead isotope rods (206Pb and 208Pb). The maximum Laser Compton Scattering gamma-ray beam energy was 5528 keV and the gamma-rays flux was greater than 107 photons/s after collimation. A two-dimensional image of 208Pb isotope distribution was selectively obtained using an exited state in 208Pb at 5512 keV.

A mid-infrared Free Electron Laser (MIR-FEL) is a candidate to realize a high-repetition-rate attosecond hard X-ray source based on the high harmonic generation (HHG). A new project to conduct proof of principle experiment of HHG driven by a MIR-FEL has been started from November 2018. For this purpose, upgrade projects of MIR-FEL at Kyoto University (KU-FEL) has been started to achieve high peak power and ultra-short pulse operation.

Photocurrent of CeB6 was measured over wide range of temperature. The photocurrent at high temperature exceeds the value expected by the Fowler-DuBridge theory. A transmission coefficient was introduced to the photoemission equation in order to account for electron escape probability. The fitting of measured data reveals that the transmission coefficient can not explain the rise in photocurrent at high temperatures for different photonenergies.

Melanin is rigidly constructed by several nitrogen-containing aromatic rings, and its excess accumulation in skin tissue is closely associated with melanosis. Although visible lasers (wavelength: 600-1000 nm) are conventionally used for the photo-thermolysis of melanocyte, several pigmented nevi are difficult to be treated. Here, we propose an alternate method for targeting the molecular structure of melanin using an infrared free-electron laser (FEL) tuned to 5.8 μm that corresponds to the stretching vibrational mode of carboxylate group. A drastic morphological change on the black-colored surface of melanin powder was observed after the pulse irradiation with power energy of 500 mJ cm-2 , and the minimum irradiation time for damage to the morphology was 1.4 s. Analyses by mass spectroscopy, infrared spectroscopy, and 13 C-nuclear magnetic resonance implied that a pyrrole group was removed by the FEL irradiation. In addition, the FEL irradiation dispersed almost all of the melanoma cells from a culture solution without any influence on other ingredients in the medium, and one-cell analysis by infrared microscopy showed that the structure of melanoma could be substantially damaged by the irradiation. This study proposes the potency of intense mid-infrared laser as novel alternative way to reduce melanin.

A magnetic chicane bunch compressor for a new compact accelerator-based terahertz (THz) radiation source at the Institute of Advanced Energy, Kyoto University, was completely installed in March 2016. The chicane is employed to compress an electron bunch with an energy of 4.6 MeV generated by a 1.6-cell photocathode radio frequency (RF)-gun. The compressed bunch is injected into a short planar undulator for THz generation by coherent undulator radiation (CUR). The characteristics of the bunch compressor and the compressed bunch were investigated by observing the coherent transition radiation (CTR). The CTR spectra, which were analyzed by using a Michelson interferometer, and the compressed bunch length were also estimated. The results were that the chicane could compress the electron bunch at a laser injection phase less than 45 degrees, and the maximum CTR intensity was observed at a laser injection phase around 24 degrees. The optimum value of the first momentum compaction factor was around &minus, 45 mm, which provided an estimated rms bunch length less than 1 ps.

Combining the nuclear resonance fluorescence (NRF) transmission method with computed tomography (CT) can be a novel method for imaging the isotope distributions, which is indispensable in nuclear engineering. We performed an experiment to reconstruct a three-dimensional NRF-CT image with isotope selectivity of enriched lead isotope rods (208Pb) together with a set of different rods, including another enriched isotope (206Pb), iron, and aluminum rods, inserted into a cylindrical aluminum holder. Using a laser Compton scattering (LCS) gamma ray beam with a 5.528 MeV maximum energy, 2 mm beam size, and 10 photon·s−1·eV−1 flux density, which is available at the BL1U beamline in the ultraviolet synchrotron orbital radiation-III (UVSOR-III) synchrotron radiation facility at the Institute of Molecular Science at the National Institutes of Natural Sciences in Japan, and we excited the Jπ = 1− NRF level at 5.512 MeV in 208Pb. An isotope-selective three-dimensional NRF-CT image of the 208Pb isotope distribution was experimentally obtained for the first time with a pixel resolution of 4 mm in the horizontal plane.

We produced intense coherent synchrotron radiation (CSR) in the terahertz (THz) region using an S-band linac at the Kyoto University Free Electron Laser (KU-FEL), which is a mid-infrared free-electron laser facility. The CSR beam was emitted from short-pulse electron bunches compressed by a 180° arc, and was transferred to air at a large solid angle of 0.10 rad. The measured CSR energy was 55 μJ per 7 μs macropulse, and KU-FEL was one of the most powerful CSR sources in normal conducting linear accelerator facilities. The CSR spectra were measured using an uncooled pyroelectric detector and a Michelson-type interferometer designed specifically for the KU-FEL electron beam, and had a maximum at a frequency of 0.11 THz. We found that adjusting the energy slit enhanced the CSR energy and shortened the electron beam bunch length in the CSR spectra measurements. Our results demonstrated that the efficient use of the energy slit can help improve the characteristics of CSR.

A compact seeded terahertz (THz) free-electron laser (FEL) amplifier is under development at the Institute of Advanced Energy, Kyoto University. The system consists of a 1.6-cell S-band BNL-type photocathode radio frequency (RF) gun, a focusing solenoid magnet, a magnetic bunch compressor, focusing quadrupoles, a short planar undulator and a THz parametric generator for seeding. The accelerator system will generate a high brightness ultra-short electron bunch injected to the short undulator. Since characteristics of the emitted radiation strongly depend on the electron beam properties, the beam dynamics of the system has been investigated. As the result, the system should be operated at the high accelerating voltage of 80 MV/m to avoid the space-charge effect which causes serious bunch lengthening. The laser with the uniform temporal distribution and the injection phase of 12 degree is suitable for the bunch compression in the chicane. This condition provides the electron beam injected to the undulator with the peak current of more than 300 A and the FWHM bunch length of 0.36 ps at the bunch charge of 200 pC., CoE on Sustainable Energy System (Thai-Japan), Faculty of Engineering, Rajamangala University of Technology Thanyaburi (RMUTT), Thailand

A mid-infrared Free Electron Laser (FEL) named as Kyoto University FEL (KU-FEL) has been developed for energy-related research at Institute of Advanced Energy, Kyoto University. The wavelength range of KU-FEL is 3.6 - 23 μm and opened for various user experiments. A compact THz-FEL, which consists of a photocathode RF gun, a bunch compressor, and an undulator, is now under construction. Present status and perspective of the FEL facility at Kyoto University is reported in this paper.

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 T 2 g optical phonon mode in single-crystal diamond at 1 , 332 cm − 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 T 2 g for the sample at cryogenic temperature, where all other modes were suppressed. The signal was observed at T 2 g phonon energy with red-shift of the peak to 1 , 306 cm − 1 , which was accompanied by surface damage induced by intense laser irradiations.

A THz coherent undulator radiation (THz-CUR) source has been developed at the Institute of Advanced Energy, Kyoto University. A photocathode Radio-Frequency (RF) gun and a bunch compressor chicane are used for generating short-bunch electron beams. When the electron beam energy is low, the space-charge effect strongly degrades the beam quality, such as the bunch length and the energy spread at the high bunch charge condition at around 160 pC, and results in the reduction of the highest frequency and the maximum radiated power of the THz-CUR. To mitigate the space charge effect, we have investigated the dependence of the electron beam quality on the laser distribution in transverse and longitudinal directions by using a numerical simulation code, General Particle Tracer GPT. The manipulation of the laser distribution has potential for improving the performance of the THz-CUR source. The electron bunch was effectively compressed with the chicane magnet when the laser transverse distribution was the truncated Gaussian profile, illuminating a cathode. Moreover, the compressed electron bunch was shortened by enlarging the laser pulse width. Consequently, an enhancement of the radiated power of the THz-CUR has been indicated.

An infrared Free Electron Laser (FEL) facility has been developed for energy-related researches at Institute of Advanced Energy, Kyoto University. The facility has two accelerator based infrared light sources. One is the mid-infrared FEL (MIR-FEL) which consists of an RF gun, a 3-m accelerator tube, a 1.8-m undulator and a 5-m optical resonator. The tunable range of the MIR-FEL is from 3.5 to $23 \ \mu \mathrm{m}$ . The RF gun can be operated with thermionic emission and photoelectron emission. The other one is the THz Coherent Undulator Radiation (THz-CUR) source which consists of a photocathode RF gun, a bunch compression chicane and a 70-cm undulator with the period length of 7 cm, The present statuses of those accelerator-based light sources are reported.

To generate an intense quasi-monochromatic Terahertz Coherent Undulator Radiation (THz-CUR), a compact linac system, which employs a magnetic electron bunch compressor with a beam energy of 4.6 MeV, has been constructed at Kyoto University. The THz-CUR has suc-cessfully been generated in a frequency range from 0.16 to 0.65 THz with a bunch charge of 60 pC. The maximum micro-pulse energy of THz radiation was observed higher than 1 μJ at 0.16 THz with 160 pC. However, when a bunch charge was higher than 80 pC, the micro-pulse energy of THz radiation gradually went to the saturation and obviously at the bunch charge higher than 110 pC because of the bunch lengthening and degradation of electron beam quality due to the space charge effect. The dependence of a bunch length on a bunch charge has been studied by GPT simulation and compared with CTR and CUR experiments. The trends of the measured results from CUR and CTR are in good agreement with the GPT simulation., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The behavior of submicrometer-sized thin-film YBa 2 Cu 3 O 7-x (YBCO) detectors under illumination with picosecond terahertz (THz) pulses was investigated. Real-time measurements with a temporal resolution of 15 ps full width at half maximum were performed at ANKA, the synchrotron facility of Karlsruhe Institute of Technology, and the UVSOR-III facility at the Institute for Molecular Science in Okazaki, Japan. The capability of YBCO detectors to reproduce the shape of a several picosecond long THz pulse was demonstrated. Single-shot measurements adhering to a reversal of the direction of the electrical field of the THz radiation were carried out. They provided evidence for the electrical field sensitivity of the YBCO detector. Exploiting the electrical field sensitivity of the YBCO detector, the effect of microbunching was observed at UVSOR-III.

We report the characterization of mid-infrared free-electron laser (FEL) beams at the wavelength of 11 μ m by the knife-edge method. From the knife-edge data we find that the FEL beam has a non-Gaussian shape. To represent the non-Gaussian beam shape we employ two methods: fitting the knife-edge data to some analytical functions with a few free parameters and numerical smoothing of the knife-edge data. Both methods work equally well. Using those data we can reconstruct the two-dimensional (2D) beam profiles at different positions around the focus by assuming that the 2D intensity distribution function is separable in x (horizontal) and y (vertical) directions. Using the 2D beam profiles at different positions around the focus, we find that the beam propagation factor ( M 2 factor) is ∼ 1.1 in both x and y directions. As a cross-check, we also carry out the burn pattern experiment to find that the behavior of the focused FEL beam along the propagation is consistent with the results obtained by the knife-edge method.

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.

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 10 4 times.

An infrared Free Electron Laser (FEL) facility has been developed for energy-related research at Institute of Advanced Energy, Kyoto University. The facility consists of an RF gun, a 3-m accelerator tube, a 1.8-m undulator and a 5-m optical resonator. The tunable range of this facility is from 5 to 20 μΜ in wavelength. The RF gun can be operated with thermionic emission and photoelectron emission. The current status and future plan of the FEL facility is reported.

Mode-selective phonon excitation induced by MIR-FEL laser irradiation on a bulk 6H-SiC has been investigated by anti-Stokes (AS) Raman scattering spectroscopy using pico-second laser. We observed a clear peak at 965 cm−1 which corresponds to the absorption energy of the lattice vibration of 6H-SiC when the pump laser wavelength was 10.4 μm (962 cm−1). However, two peaks were observed by slightly detuned pump laser wavelength. Results of time resolved measurement suggested that the origin of these peaks were AS Raman scattering and sum frequency generation on 6H-SiC sample.

We carry out the time-resolved detection of structural change in dye-doped crystalline polymer films upon laser-heating and subsequent natural cooling.

Inverse Compton-scattered gamma rays of tunable energy were generated by changing the collision angle between a laser and an electron beam of fixed energy at the electron storage ring, UVSOR-II. Analytic expressions were derived for energy and intensity of the gamma rays. The measured energy and intensity of the gamma rays agreed with the theoretical values, and the pulse width was calculated to be a few ps, under experimental conditions. It was shown that ultra-short gamma ray pulses with a pulse width of 150 fs can be generated by optimizing the size of the laser spot.

Terahertz (THz) coherent synchrotron radiation (CSR) is emitted not only from ultra-short electron bunches, but also from electron bunches with micro-structures. Formation of micro-structures at the sub-picosecond scale in electron bunches by a laser slicing technique is experimentally studied through observation of the THz CSR. The THz CSR spectrum was found to depend strongly on the intensity and the pulse width of the laser. The results agreed qualitatively with a numerical simulation. It was suggested that the evolution of the micro-structure during CSR emission is important under some experimental conditions.

The energy levels of electron traps (namely, defect complexes associated with oxygen vacancies) in Gd3Al2Ga3O12:Ce (GAGG:Ce) were studied at 12 K using mid-infrared (MIR) light pulses from a free-electron laser (FEL) as the probe light. Ce3+ 5d–4f luminescence was stimulated by the MIR light pulse following an ultraviolet light pulse. Stimulation of Ce3+ 5d–4f luminescence by MIR light pulses was pronounced above 0.31 eV. This result is consistent with that of previous work based on a trap-mediated luminescence model. It is concluded that the electron trap levels are located 0.31 eV below the bottom of the conduction band. This study demonstrates that MIR-FEL is applicable for the determination of hidden electron trap levels.

A diagnostic method for spatial distributions of D-D and D- 3 He fusion reactions has been developed. Refinement of collimation geometry and choice of a detector and a shielding foil resulted in a drastic improvement of signal separation from noise in collimated proton counting. The developed method was then applied and revealed proton yield distributions in an inertial-electrostatic confinement device running with a D 2 - 3 He mixture fuel gas. The result showed localized D- 3 He reactions on cathode gird surfaces. It also indicated considerable fractions of D-D reactions on anode grid and chamber wall surfaces as well as the cathode grid.

A thermionic RF gun usually suffers from a rapid decrease of electron beam energy caused by a rapid increase of beam current due to the back-bombardment effect. The authors propose a new method named ldquocavity detuningrdquo to keep the electron beam energy constant. This method detunes the resonant frequency of the gun cavity to a frequency that is lower (by several hundred kilohertz) than the driving frequency. A proof-of-principle experiment was carried out using a 4.5 cell S-band RF gun. The beam energy was successfully kept constant during a macro-pulse duration of 7.5 mus using a cavity detuning of -590 kHz, even with a significant current increase from 240 to 660 mA. A numerical simulation was also conducted to evaluate the cathode temperature, the current density on the cathode surface, and the phase stability of the output beam. All results demonstrated that cavity detuning provides an easy and simple way to compensate for the energy decrease in thermionic RF guns.

Laser amplification using a 12 µm mid-infrared free-electron laser (MIR-FEL) was observed at the Institute of Advanced Energy (IAE), Kyoto University. A 25 MeV electron beam of 17 A peak current was used for the lasing experiment. A beam loading compensation method with an RF amplitude control in the thermionic RF gun was used to extend the macropulse duration against the backbombardment effect in the thermionic RF gun. As a result, an electron beam with a 4 µs duration was generated. A laser output with an intensity 50 times as high as the spontaneous emission intensity was observed. FEL gain was estimated to be 16% from the exponential growth of the laser output signal, and a cavity loss of 2.8% was estimated from the decay of the laser output signal. Three-dimensional (3D) FEL simulation was also performed to achieve the gain saturation in our FEL device.

A mid-infrared free electron laser (FEL) has been constructed for energy science in the Institute of Advanced Energy, Kyoto University. The FEL system consists of a compact S-band Linac and an undulator to generate 4–13 μm coherent mid-infrared radiations. The Linac consists of a 4.5 cell rf gun with a thermionic cathode and a 3-m traveling-wave-type accelerator tube fed by 10 MW and 20 MW rf power, respectively. We have succeeded to produce 40 MeV, 40 mA and 3 μs electron beams. Last December, the 9.2 μm spontaneous emission from the undulator generated by 29.5 MeV electron beams was observed for the first time. Further optimization parameters of both the electron beam and the optical cavity are being pursued for an FEL lasing in the near future.

We are developing a compact seeded terahertz (THz) free-electron laser (FEL) amplifier at the Institute of Advanced Energy, Kyoto University. The system consists of a photocathode RF-gun, a focusing solenoid magnet, a magnetic bunch compressor, focusing quadrupoles, an undulator, a laser system for the RF-gun and a THz parametric generator for seeding. The seeded THz lasers are amplified by FEL interaction inside the undulator. The target radiation wavelength is 300 to 800 μm. As the first step of the development, we evaluate expected power of coherent synchrotron radiations (CSRs). As the result it is found that the bunch charge from 50 to 75 pC will be suitable operation condition.

An active non-destructive detection system for special nuclear materials (SNMs) such as 235U has been developed for container inspection at sea ports. The SNMs can be detected by using nuclear resonance fluorescence (NRF) with a quasimonochromatic gamma-ray beam provided from a laser Compton Scattering (LCS) source. We have studied the optimum geometry for the detector array by Monte Carlo simulation code, GEANT4, which has been modified to take into account all physical processes in NRF. The simulation code has been checked by the experimental data taken in New-SUBARU and HIgS facility. NRF yield at different scattering angles were examined with different thickness of 235U target. The result shows that the backward angle is the optimum geometry for NRF detection in terms of NRF yield and S/N ratio caused by atomic scattering. Realistic simulation for a container cargo has been performed. Detector array of 100 LaBr 3 (Ce) detectors has been examined with 3 different size of crystals. Consequently, we can demonstrate the ability of the proposed inspection system.

The possibility of the post-manufacturing control of the macroscopic critical current density by the low-fluence high-energy proton irradiation was studied for cm sized bulk high temperature superconductor. The irradiations of 200 MeV protons on bulk DyBaCuO samples with the fluence of from 2.3 × 10 10 to 1.2 × 10 12 protons/cm 2 were performed. The maximum magnetic flux densities on the sample surfaces were increased by up to 80% after proton irradiation. This value of the increment is larger than the individual differences of the bulk high temperature superconductors just after the production. The macroscopic critical current densities seemed to be increased almost everywhere in the samples.

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.

The presence of a pulse train structure of an oscillator-type free-electron laser (FEL) results in the immediate damage of a solid target upon focusing. We demonstrate that the laser-induced damage threshold can be significantly improved by gating the mid-infrared (MIR) FEL pulses with a plasma mirror. Although the switching pulses we employ have a nanosecond duration which does not guarantee the clean wavefront of the gated FEL pulses, the high focusablity is experimentally confirmed through the observation of spectral broadening by a factor of 2.1 when we tightly focus the gated FEL pulses onto the Ge plate.

We report the pulse duration and wavelength stability measurements of a midinfrared free-electron laser (FEL) where the wavelength fluctuation may not be negligible. The technique we employ is a fringe-resolved autocorrelation (FRAC) method that has good sensitivity on not only the pulse duration and the chirp but also the wavelength stability. By the simple manipulation of experimental FRAC signals, we can obtain the pulse duration even if the amounts of the chirp and the wavelength stability are not known in advance, which is further used to estimate the wavelength stability. Through this procedure we find that the pulse duration of the Kyoto University FEL at 12 μm is about 0.58 ps without any notable chirp, and the wavelength stability is about 1.3%. We also carry out separate experiments for intensity autocorrelation and sum-frequency mixing. The difference we find for pulse duration and wavelength stability by the different measurements is attributed to the different operation conditions of FEL.

To realize short-period high-magnetic-field undulator, we have proposed an undulator using bulk high temperature superconductor in a staggered array structure. To investigate the effect of the longitudinal solenoid field on the electron beam trajectory, the magnetic field near the center of this undulator was modeled and the trajectory of the single electron and the undulator radiation was calculated. As a result, we found that the stronger solenoid field had a good effect on the electron beam confinement. However, we found that the radiation wavelength became longer and the peaks of the spectrum became smaller at stronger solenoid field.

The back bombardment (BB) effect limits wide usage of thermionic rf guns. The BB effect induces not only ramping-up of a cathode's temperature and beam current, but also degradation of cavity voltage and beam energy during a macropulse. This paper presents a comparison of the BB effect for the case of dispenser tungsten-base (DC) and lanthanum hexaboride (${\mathrm{LaB}}_{6}$) thermionic rf gun cathodes. For each, particle simulation codes are used to simulate the BB effect and electron beam dynamics in a thermionic rf gun cathode. A semiempirical equation is also used to investigate the stopping range and deposited heat power of BB electrons in the cathode material. A numerical simulation method is used to calculate the change of the cathode temperature and current density during a single macropulse. This is done by solving two differential equations for the rf gun cavity equivalent circuit and one-dimensional thermal diffusion equation. High electron emission and small beam size are required for generation of a high-brightness electron beam, and so in this work the emission properties of the cathode are taken into account. Simulations of the BB effect show that, for a pulse of $6\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$ duration, the DC cathode experiences a large change in the temperature compared with ${\mathrm{LaB}}_{6}$, and a change in current density 6 times higher. Validation of the simulation results is performed using experimental data for beam current beyond the gun exit. The experimental data is well reproduced using the simulation method.

Thermionic RF guns have advantageous features, such as compactness and high brightness of output beam, against electrostatic guns because of their high acceleration fields. For these reasons, thermionic RF gun has been ­chosen as electrons injector for Kyoto University free electron laser facility. The most critical issue of the thermionic RF gun is the transient cathode heating due to the electron back-bombardment when the gun is used as a driver linac of an MIR–FEL oscillator, which requires macropulse duration of more than 5 μs and bunch charge of more than 20 pC. Under the condition, the transient cathode heating results in rapid increase of beam current and rapid decrease of beam energy during a macropulse. Several important parameters, such as cathode temperature, current density of the cathode surface, are difficult to be measured during the experiment. A numerical simulation is the best way to expect the behaviour of such parameters. Numerical calculations were carried out to evaluate the cathode temperature and current density during the macropulse, by a simulation code which was developed at Kyoto University. The code simultaneously solves two differential equations; the differential equation of the equivalent circuit of the RF gun and one dimensional thermal equation of the thermionic cathode which includes the heat input from back-bombardment electrons. The results of transient response of the RF cavity due to the back-bombardment effect are presented with conclusions.

Top‐up operation was successfully demonstrated at UVSOR‐II, which will remove the short beam‐lifetime problem caused by strong Touschek effect due to the small emittance, 27 nm‐rad, and the low electron energy, 750 MeV. In these years, we have improved the accelerators, step by step, towards top‐up operation. The radiation shielding wall was reconstructed. The energy of the booster synchrotron and the beam transport line were successfully upgraded from 600 MeV to 750 MeV, by replacing the magnet power supplies in 2006. Soon after, we succeeded in injecting the electron beam at the full energy. We improved the radiation safety system and constructed a injection control system. In autumn, 2008, we succeeded in operating the ring for 12 hours as keeping the beam current quasi‐constant at 300 mA. Currently, we operated the ring in the top‐up mode for 12 hours on every Thursday night, to check the effects on the users’ experiments. In 2009, we have succeeded in the top‐up operation in single bunch mode. Free e...

Electric field of coherent synchrotron radiation produced by laser bunch slicing at a storage ring has been measured for the first time. A 24 m-long fiber was used to deliver the probe for electro-optic sampling.

We are developing coherent light sources at the UVSOR‐II electron storage ring. We have developed a resonator type free electron laser in the visible to the deep UV range, coherent harmonic generation source in VUV range and coherent synchrotron radiation source in the terahertz range. A new five year plan has been started from FY2008, where a new 4m straight section will be created by moving the beam injection point, a new optical klystron type undulator will be installed and dedicated beam‐lines will be constructed. Great advances on the coherent light source developments at the new straight section are expected.

An inertial electrostatic confinement (IEC) fusion device can produce copious amount of neutrons and protons from D-D and D-3He fusion reactions using D2 and 3He fuels. In IEC researches aiming at drastically enhanced neutron/proton yields, understanding the intensity distribution of fusion reactions is one of the most intensive interests. In order to make clear the spatial distribution of D-3He fusion reaction rate in an IEC device, we analyzed the experimentally observed proton count rates as function of collimation geometry by use of most likelihood-expectation maximization (ML-EM) method. Requirements of the measurement system were studied for reconstructing the D-3He reaction distribution, especially on the feedthrough surface that has been neglected so far, and an upgrade measurement system was developed and introduced in this study. From the experimental results, we found that more than 99 % of the D-3He fusion reactions occur on the cathode and feedthrough surfaces.

Energy degradation due to back‐bombardment effect is quite serious to produce high‐brightness electron beam with long macro‐pulse with thermionic rf gun. To avoid the back‐bombardment problem, a laser photo cathode is used at many FEL facilities, but usually it costs high and not easy to operate. Thus we have studied long pulse operation of the rf gun with thermionic cathode, which is inexpensive and easy to operate compared to the photocathode rf gun. In this work, to reduce the energy degradation, we controlled input rf power amplitude by controlling pulse forming network of the power modulator for klystron. We have successfully increased the pulse duration up to 4 μs by increasing the rf power from 7.8 MW to 8.5 MW during the macro pulse.

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.