M. Nakatsuka

Laser-induced Mg production from magnesium oxide using Si-based agents and Si-based agents recycling

We succeeded in laser-induced magnesium (Mg) production from magnesium oxide (MgO) using Si-based agents, silicon (Si) and silicon monoxide (SiO). In these experiments, a cw CO2 laser irradiated a mixture of Mg and Si-based agents. Both experimental studies and theoretical analysis help not only understand the function of reducing agents but also optimize Mg extraction in laser-induced Mg production. The optimal energy efficiencies 12.1 mg/kJ and 4.5 mg/kJ of Mg production were achieved using Si and SiO, respectively. Besides, the possibility of recycling Si and SiO was preliminarily investigated without reducing agents but only with laser-irradiation. As for the Si-based agents recycling, we succeed in removing 36 mol % of oxygen fraction from SiO2, obtaining 0.7 mg/kJ of Si production efficiency as well as 15.6 mg/kJ of SiO one at the same time. In addition, the laser irradiation to MgO-SiO mixture produced 24 mg/kJ of Si with more than 99% purity.

Study on Liquid Lithium Target System for Boron Neutron Capture Therapy (BNCT)

The concept of the liquid lithium target system for the boron neutron capture therapy (BNCT) using an accelerator was formulated. A lithium flow loop was designed and fabricated for development of lithium jet nozzles that provide a stable lithium plane jet. A water flow loop was designed, fabricated and used for development of lithium jet nozzles. Experiment of water plane jet was conducted to investigate the stability of high velocity plane jets. A large amount of droplets were entrained from the jet surface when the jet was unstable. The jet was observed by being illuminated with a stroboscope. It was found that a stable plane jet was realized by using a nozzle with the gap of 0.5mm and the length of 70mm. It was concluded that a fully developed flow without inlet disturbances at the outlet of the nozzle was required for the stability of the high velocity plane jet.Copyright

Laser‐induced Magnesium Production from Magnesium Oxide for Renewable Magnesium Energy Cycle.

We succeeded in reducing magnesium [Mg] from magnesium oxide [MgO] by laser irradiation. The laser‐induced vapor temperature was measured to be approximately 5000 K on the irradiating spot, where MgO separated into Mg and oxygen [O] atoms through thermal dissociation. The Mg vapor was intercepted a cooper plate, forming solid deposits on it. However, the presence of oxygen, resulting from MgO dissociation, leads to Mg oxidization in the course of vapor cooling. The deoxidization process results in lower Mg fraction in the deposits and degrades energy recovery efficiency from laser irradiation. To quench this recombination, we also employed silicon as reducing agents to capture oxygen in favor of Mg extraction. In these experiments, the molar ratio effect (MgO:Si = 1:0–1) on the magnesium fractions and energy efficiencies were measured by means of a chemical reaction. The maximal energy efficiency, %, was obtained at the ratio of MgO:Si = 1:0.5. This ratio is lower than that of the Pidgeon process with Mg:...

Control of gray-tracking formation for KTP and LBO crystals

Gray-tracking formations for KTP crystals were controlled by thermal annealing process before laser irradiation because hydroxyls in the crystals were controllable. The formation was suppressed with increasing the annealing temperature and humidity. LBO crystals were also examined.

Control of gray-tracking formation in KTiOPO/sub 4/ crystals by thermal annealing preprocess

Summary form only given. The KTiOPO/sub 4/ (KTP) crystal was used for second-harmonic generation (SHG) of high-average-power lasers because it has a large nonlinear optical coefficient and a wide temperature bandwidth. However, the crystal has one disadvantage, i.e., gray-tracking formation. The gray-tracking was investigated by many workers. The gray-tracking susceptibility (GTS) was different for individual crystal. To understand the gray-tracking formation, many crystals from different growth techniques should be compared. Relationship between the absorption coefficient and the GTS or the impurities for different KTP crystals was investigated. Finally, we propose a new approach to improve the gray-tracking.

10 J/spl times/10 Hz diode-pumped Nd:glass slab laser amplifier

Summary form only given. Diode-pumped solid-state laser (DPSSL) is one of promising candidates as reactor driver for IFE. We have been developing a 10-J output class of diode-pumped water-cooled Nd:glass zig-zag slab laser amplifier module as a smallest-scale test-version of our conceptually designed 4-MJ DPSSL driver. We will show the experimental confirmation of our conceptual design through the investigation of 10-J/spl times/10-Hz module on the key issues such as small signal gain, energy extraction, stored energy, pumping efficiency, thermal effects, beam quality and heat flow in the system.

10J x 10 Hz Diode-pumped Nd: glass slab amplifier for inertial fusion energy

We have conceptually designed a diode-pumped Nd: glass slab amplifier module for Inertial Fusion Energy (IFE). As a first step of a driver development, we have been developing a diode-pumped zig-zag Nd: glass slab laser amplifier system which can generate an output energy of 10 J per pulse at 1053 nm in 10 Hz operation. The water-cooled zig-zag Nd:glass slab is pumped from both sides by 803-nm AlGaAs laser-diode (LD) module; each LD module has an emitting area of 420 mm x 10 mm and two LD modules generated in total 200kW peak power with 2.5kW/cm2 peak intensity at 10 Hz repetition rate. We have obtained in a preliminary experiment a 8.5 J output energy at 0.5 Hz with beam quality of 2 times diffraction limited far-field pattern.

Development of LD pumped 10 J/spl times/10 Hz Nd:glass slab laser

The concept of a diode-pumped solid-state laser (DPSSL) driver for inertial fusion energy (IFE) has been introduced by Krupkel (1989), and Naito et al. (1992). Orth et al. (1996) has designed in detail a DPSSL driver using He gas cooling. In the study, we have developed a conceptual design of a 803-nm laser-diode (LD) pumped water-cooled Nd:glass slab laser driver for IFE. The IFE power plant KOYO has the basic design specifications of 4 MJ output at 351 nm and 12 Hz repetition rate. For the laser gain medium, we have adopted the glass host which can be produced in large sizes with good optical quality. The HAP-4 glass (HOYA) has the appropriate material parameters for designing a high power and repetitively operating laser system. The slab dimensions were determined under the several operational constraints. Zig-zag path slab has an advantage that the laser beam does not pass through the cooling medium as it propagates by means of total internal reflections. Using this advantage, the slab is cooled on both sides with flowing water having high cooling capability. As a first step of a driver module development for the IFE, we are developing a small scale DPSSL module which has 10 J x 10 Hz laser output at 1053 nm. The module is the smallest size to confirm the conceptual design of the driver module.

Optically-written distributed phase and polarization plates of liquid crystal as power photonics elements

A pattern formation of the laser beam with polarization control was demonstrated by UV written patterning of the liquid crystal cell that had high laser damage threshold over 10 J/cm2 at 1 to 0.5 micron in wavelength and 1 ns pulse duration. The serrated soft aperture was fabricated by this procedure. A new kinoform plate is proposed for an application of the distributed phase plate as a beam focus control in the laser fusion experiment.