Goro Isoyama

Lasing of a free electron laser in the visible on the UVSOR storage ring

Abstract We have conducted oscillation experiments of a free electron laser on the UVSOR storage ring. In the experiments the storage ring was operated in the two-bunch mode at an electron energy of 500 MeV and an optical klystron was employed. Dielectric multilayer mirrors with high reflectivity at a wavelength around 455 nm were used for an optical resonator. When the beam current is higher than 9 mA/bunch, lasing started at 456 nm. The lasing wavelength can be varied in the region from 430 nm to 480 nm. The linewidth of the laser is approximately 0.2 nm. The peak power in micro-pulses transmitted by the front mirror is roughly estimated to be at least 0.8 W at a beam current of 23 mA/bunch.

FEL experiment on the UVSOR storage ring

Abstract A gain-enhancement technique using a higher harmonic cavity has been developed for free electron laser experiments on the UVSOR storage ring. With this technique, we obtained lasing in the ultraviolet region at wavelengths around 300 nm. Applying gain-switching to control lasing, effective gain was derived at a wavelength of 490 nm, which was in good agreement with the theoretical prediction.

Observation of micro-macro temporal structure and saturation mechanism on the UVSOR free electron laser

Abstract The dynamic behavior of a free electron laser oscillation on an electron storage ring has been studied. We have measured time dependent micropulse evolution using a streak camera with a dual-sweep. Continuous lasing which appears under detuned condition has been ascertained to consist of discrete evolving groups of micropulses. In the gain-switching mode, bunch lengthening of the electrons due to bunch heating by the interaction with the laser was clearly observed.

Control of the bunch length on an electron storage ring

Abstract We report on an experiment to control bunch length by means of changing the momentum compaction factor on the UVSOR storage ring. The momentum compaction factor was varied by changing the dispersion function, and reduced to be approximately one hundredth of the ordinary value. The shortest bunch length estimated from the synchrotron oscillation frequency was 25 ps, which is one tenth of the ordinary value. Correction for the second order momentum compaction factor was found to be essential for operation with the extremely low momentum compaction factor. The results of measurement of the momentum compaction factor and the bunch length are presented.

Polymer Morphological Change Induced by Terahertz Irradiation

As terahertz (THz) frequencies correspond to those of the intermolecular vibrational modes in a polymer, intense THz wave irradiation affects the macromolecular polymorph, which determines the polymer properties and functions. THz photon energy is quite low compared to the covalent bond energy; therefore, conformational changes can be induced “softly,” without damaging the chemical structures. Here, we irradiate a poly(3-hydroxybutylate) (PHB) / chloroform solution during solvent casting crystallization using a THz wave generated by a free electron laser (FEL). Morphological observation shows the formation of micrometer-sized crystals in response to the THz wave irradiation. Further, a 10−20% increase in crystallinity is observed through analysis of the infrared (IR) absorption spectra. The peak power density of the irradiating THz wave is 40 MW/cm2, which is significantly lower than the typical laser intensities used for material manipulation. We demonstrate for the first time that the THz wave effectively induces the intermolecular rearrangement of polymer macromolecules.

Construction and commissioning of a superconducting wiggler for the UVSOR storage ring

Abstract A 4-T superconducting wiggler of the wavelength-shifter type has been constructed and commissioned for experiments in the photon energy region above 2 keV at the 750-MeV UVSOR storage ring. It has a semi-closed liquefying system with two refrigerators that can confine liquid helium without loss. It has been confirmed that the wiggler can continuously run for one year without trouble. A feasibility study on low magnetic field operation of the wiggler was conducted for experiments with the lower photon energies below 2 keV using a double crystal monochromator with beryl crystals.

Measurement of the Bunch Length on the UVSOR Storage Ring

We have measured the bunch length in single-bunch operation of the UVSOR (Ultraviolet Synchrotron Orbital Radiation) storage ring in a beam current region from 0.1 to 70 mA at energies ranging from 500 to 750 MeV. The momentum compaction factor of the present operation point is determined experimentally from the bunch length and the synchrotron oscillation frequency measured simultaneously at a low beam current. The bunch length increases gradually as the beam current increases, and bunch lengthening is larger when the beam energy is lower. This behavior of bunch lengthening agrees well with a prediction of the potential-well distortion theory. Based on the theory, the effective longitudinal coupling impedance is estimated as a function of bunch length.

Magnet lattice for the Siam Photon Source

The magnet lattice for the Siam Photon Source, the first storage ring for synchrotron radiation research in Thailand, has been designed. The storage ring has a double-bend achromat lattice and fourfold symmetry with four straight sections. Although the magnet lattice is relaxed, an emittance value of 72 pi nm rad has been obtained, which is only 1.4 times as large as the theoretical minimum emittance with eight bending magnets. The dynamic aperture is found to be much larger than the physical aperture.

Present status of the UVSOR light source

Abstract The UVSOR storage ring and its present status are presented. Technical problems related to the beam instability, beam lifetime and single bunch operation are described, as well as cures for them. A new superconducting wiggler and a free electron laser project on the storage ring are introduced.

Landau Damping of the Longitudinal Coupled-Bunch Instability in an Electron Storage Ring

A longitudinal coupled-bunch instability of the beam current in an electron storage ring was damped successfully by using a Landau cavity. This results in the reduction of beam size and the suppression of the slow fluctuation of the synchrotron radiation