Masahiro Nakatsuka

Heavy fluorocarbon liquids for a phase-conjugated stimulated Brillouin scattering mirror.

Heavy fluorocarbon liquids were found to be an ideal medium for high-power stimulated Brillouin scattering experiments. Fluorinert FC-75 gives high reflectivity, near 98%, and excellent fidelity in phase conjugation of 14-J, 18-ns optical pulses. The complete removal of microparticle impurities was found to be essential for avoiding laser damage in a high-energy operation. A method of purification based on ultrafiltration has been developed.

Diode-Pumped Zig-Zag Slab Laser for Inertial Fusion Energy and Applications

A quasi-cw 290-kW diode-pumped zig-zag slab laser is being developed in order to demonstrate a concept of the IFE driver. Thermally managed amplifier has yielded a gain of 10, promising 10-J output at 10 Hz.

Liquid-cooled ceramic Nd:YAG split-disk amplifier for advanced high-average-power laser

A liquid-cooled ceramic Nd:YAG split-disk amplifier have been designed and demonstrated of 3.7-cm clear aperture with the compensation of wavefront degradation due to cooling and the small-signal gain was measured.

Diode-Pumped Thermally Controlled Zig-Zag Slab Laser with 20-J Pulse Energy in 10 ns at 10-Hz Repetition Rate

20-J pulse energy in 10 ns at 10 Hz thermally controlled zig-zag slab laser based on the scaling law up to 100 J is being demonstrated by 800-kW peak pump power from 8,000 diode bars.

Temperature dependences of fluorescence characteristic for Nd/Cr:YAG materials

Cr3+ co-doped Nd:YAG is very useful for the flashlamp or solar pumped laser through Cr3+ ion has broad absorption bands in the visible region and an efficient energy transfer caused from Cr3+ to Nd3+. But the process of the energy transfer is not understood well. It is also a problem that the absorption at near infrared is appeared with changes of Cr3+ to Cr4+. We investigated these problems by measuring the temperature dependence of fluorescence characteristics (lifetime, excitation fluorescence and absorption) and the change after UV irradiation. The excitation fluorescence spectra at 450 K increased because the Cr3+ absorption depended on temperature. The fluorescence lifetime excited at the Cr3+ absorption bands shortened with increase temperature, that is, the energy transfer time will be short. Solarization was appeared in Nd/Cr:YAG ceramics irradiated by KrF excimer laser pulses at 248 nm.

Pre-evaluation method for the spectroscopic properties of YAG bulk materials by sol-gel synthetic powder

The sol-gel synthetic powder evaluation method is the most effective and the easiest technique for pre-evaluating the spectroscopic properties of luminescent impurity doped YAG. The luminescent elements doped sol-gel powder agrees well with that of a single crystal or ceramic YAG regarding the luminescent spectra, the intensity, and the lifetime, even though the powder sintered at a low temperature of 1100°C in comparison with the YAG crystal melting point of 1970°C, because a good crystallinity of the sol-gel powder is led by the hard agglomerates of very small primary particles. It is considered that the significance of this method is to apply for not only of YAG but also of other oxides, for instance Y2O3, ZrO2, TiO2, and MgAl2O4

High Repetition and High Average Power Nd:YAG Laser for EUV Lithography

We have been developing a high repetition (5-100 kHz) and high power Nd: YAG laser system pumped by cw LDs. Average power of 4.6 kW was obtained at 28.8 kW of pumping power.

High Pulse Energy, Rep-Rated Nd:Glass Laser with Stimulated Brillouin Scattering Phase Compensator

The near diffraction limited quality of 21.3 J in 8.9 ns (2.4 GW peak power) at 10Hz rep-rate beam has been obtained by diode-pumped Nd:glass zig-zag slab laser with a stimulated Brillouin scattering (SBS) mirror.

Efficient Wavelength Conversion Based on Periodically Poled MgO:LiNbO 3 Optical Parametric Oscillator

Optical parametric oscillator based on a large aperture periodically poled MgO:LiNbO3 was used to generate 2 µm laser. Total output of 179 mJ with 53% slope efficiency was achieved at low pump fluence.

High Power and High Repetition Nd: YAG Laser Pumped by cw Laser Diodes

We have been developing a high repetition (5 kHz) and high power (5 kW) Nd: YAG laser system pumped by cw LDs for EUV lithography. Design concepts and experimental results will be reported.