Shuji Miyamoto

Isochronous storage ring of the New SUBARU project

The aims of the New SUBARU project are to promote industrial applications in the VUV and soft X-ray region and to develop research and development towards new light sources. The main facility of the New SUBARU project is the 1.5 GeV electron storage ring which is under construction at the SPring-8 site in Harima Science Garden City, Japan. The storage ring is quasi-isochronous and has variable momentum dispersion for the deep study of beam dynamics in very short bunches.

Rotating cryogenic drum supplying solid Xe target to generate extreme ultraviolet radiation

In order to generate high-average-power extreme ultraviolet radiation around 13.5nm from laser-produced plasma, a fast rotating cryogenic drum system which can continuously supply a solid Xe target for high-repetition laser pulses has been developed. It was successfully operated at a rotating speed of 1000rpm and an up-down speed of 3mm∕s. The growth rate of the solid Xe layer is kept at a constant speed (for example, 18μm∕s) with a constant rate of Xe input flow, independent of the rotating speed. It has been demonstrated that wipers play an important role in recovering the laser craters with a recovery rate of 150μm∕s. These performances allow laser illuminations on the solid Xe target with a pulse repetition rate of 10kHz without overlapping laser craters.

X-ray generation in cryogenic targets irradiated by 1 μm pulse laser

Soft x-ray spectral radiations from Xe, H2O, and CO2 cryogenic targets irradiated by a 1 μm neodymium doped YAG-slab laser at pulse widths of 12–20 ns and at laser intensities of 5×1010–1012 W/cm2 have been observed. These targets radiate soft x-rays in a wavelength range of 10–13 nm which is useful for projection microlithography. We have found a strong x-ray spectral peak at λ=10.8 nm with a Xe cryogenic target. The measured x-ray conversion efficiency with the Xe target was 0.8%/sr(λ=10.8±0.27 nm) at a laser intensity of 1×1012 W/cm2. This was ten times or more efficient than that with H2O and CO2 targets.

Helical distributed feedback free-electron laser

Results of the implementation of a distributed feedback (DFB) reflector in a free‐electron laser (FEL) are described. The reflector was positioned in the interaction region of the FEL waveguide in order to produce narrow bandwidth features in the output spectrum. Both the DFB and wiggler were of helical configuration. The energy, current, and pulse width of the electron beam were 1.5 MeV, 100 A, and 50 ns. By employing the DFB structure the intensity of the two specific frequencies may be increased by factors of 3 and 5. These frequencies are in good agreement with those predicted by theory. Temporally radiation waveforms exhibit a double peak, revealing a sensitivity of the oscillation condition to beam energy.

Laser wavelength and spot diameter dependence of extreme ultraviolet conversion efficiency in ω, 2ω, and 3ω Nd:YAG laser-produced plasmas

Conversion efficiency and spectra of extreme ultraviolet radiations from a cryogenic planar solid xenon target were investigated as a function of laser wavelength (ω, 2ω, and 3ω Nd:YAG) and the laser focus spot size (50–700μm) at the intensity 1010–5×1012W∕cm2. The conversion efficiency increased with laser intensity and reached the maximum value at about 1011W∕cm2 for all colors. It was found that an edge effect appears more strongly at the ω-laser case, indicating more lateral energy loss, while it appears only weakly for higher harmonics. Shorter-wavelength lasers generated significant conversion efficiencies even at lower laser energies; that is, with smaller laser spots. As the wavelength decreased from ω, 2ω, and 3ω, a spectral hump appeared in the extreme ultraviolet band around 13.5nm region, while the spectral intensity at 10.8nm drastically decreased. High-energy photon generation in the tail of 10.8nm peak was found to be strongly suppressed at shorter-wavelength laser (3ω), while the conversio...

Extreme ultraviolet source using a forced recombination process in lithium plasma generated by a pulsed laser

An extreme ultraviolet source having a tamper has been studied. This target scheme recombines forcedly lithium ions by low temperature electrons from the tamper, converting Li3+ rapidly to excited Li2+ which emit intense 1s-2p Lyman α emissions at 13.5nm. A strong 13.5nm emission appeared at 20–30ns after the time of laser peak within a small space volume near the tamper. The authors obtained an enhancement of extreme ultraviolet conversion efficiency by a factor of about 2 with the tamper against that of a target without the tamper at the same laser irradiation condition.

Resonant Photonuclear Reactions for Isotope Transmutation

Resonant photonuclear isotope transmutation (RPIT) is shown to be very powerful to produce exclusively radioactive isotopes (RIs) by resonant photonuclear (γ,n) and (γ,2n) reactions via E1 giant resonances. Photons to be used are medium energy [ E (γ) ≈12–25 MeV] photons produced by laser photons backscattered off GeV electrons. The cross sections are as large as σ≈0.2–0.5 b (10 -24 cm 2 ) for all medium-heavy nuclei. A large fraction (∼3%) of photons is effectively used for the photonuclear reactions, while the scattered GeV electrons remain in most storage rings to be re-used. To demonstrate the RPIT feasibility, 99 Mo/ 99 m Tc and 196 Au RIs were produced by RPIT on 100 Mo and 197 Au with laser photons scattered off 1 GeV electrons at the NewSUBARU storage ring. RPIT with medium energy photons around 10 12–15 /s provides specific/desired RIs with the rate of 10 10–13 /s and the RI density around 0.05–50 G Bq/mg for nuclear science, molecular biology and for nuclear medicines.

Absolute calibration of imaging plate for GeV electrons

An imaging plate has been used as a useful detector of energetic electrons in laser electron acceleration and laser fusion studies. The absolute sensitivity of an imaging plate was calibrated at 1 GeV electron energy using the injector Linac of SPring-8. The sensitivity curve obtained up to 100 MeV in a previous study was extended successfully to GeV range.

Effect of Laser-Plasma X-Ray Irradiation on Crystallization of Amorphous Silicon Film by Excimer Laser Annealing

The effect of laser plasma soft X-ray (LPX) irradiation on crystallization by excimer laser annealing (ELA) was investigated at low ELA energy densities. The crystalline fraction at energy densities of 50 and 60 mJ/cm2 for LPX followed by ELA is nearly equal to that at 80 to 100 mJ/cm2 for the ELA method with non-LPX irradiation. The results obtained indicate that LPX irradiation before ELA reduces the critical energy density for the start of crystallization. The combined method of LPX irradiation and ELA will enable us to realize a low-temperature process for ELA crystallization.

Soft x-ray emissions from laser plasma of cryogenic mixture targets

Soft x-ray spectral radiation from Xe–CO2 mixture cryogenic targets with a Xe mole fraction of 0% (pure CO2) to 100% (pure Xe) irradiated by a 1 μm pulse laser at a laser intensity IL of 0.3–1.0×1012 W/cm2 has been observed. The x-ray conversion efficiency per Xe mole fraction was found to have maximum values at the Xe fractions of 10% for IL=6.0×1011 W/cm2 and 5% for IL=1.2×1012 W/cm2, which were about five and ten times as large as that in a pure Xe target, respectively. The x-ray conversion efficiencies in the cryogenic mixture targets at Xe fractions of 10%–40% were about 1.3 %/sr/nm for λ=10.8 nm and IL=1012 W/cm2, which was as high as that in a pure Xe cryogenic target. The physical mechanism behind this enhanced emission is discussed.