Masanobu Yamanaka

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.

Design and Analysis on Face-Cooled Disk Faraday Rotator for High Average Power Lasers

A novel, scalable Faraday rotator has been designed for high-average-power lasers in a gas-cooled multi-disk scheme. The concept with a negligible thermal distortion and birefringence is feasible up to 10 kW/cm2 enough below fracture limit.

Development of high-power DPSSL and its application

Driver technology is a key issue for Inertial Fusion Energy (IFE) development. A diode pumped solid-state laser (DPSSL) is expected to be a promising candidate of reactor driver for IFE. The specifications required for the IFE driver are 2-5 MJ output pulse energy, 10-20 Hz repetition rate, 500-200 nm laser wavelength, and >10% electrical efficiency. We have newly designed a Nd:YAG DPSSL driver module based on a water cooled zig-zag path slab amplifier, which can deliver 10 kJ output energy at 350 nm with 12 Hz repetition. The module consists of 15 beamlets and each beamlet is a double 4-pass amplifier system as it plays a role of both pre-amplifier (4-pass) and main amplifier (4-pass). The laser driver producing a 4 MJ blue output consists of 400 modules.

Thermal Birefringence in Cylindrical Faraday Rotator under High Average Power Lasers

Detailed computation and experimental results of thermal birefringence loss in TGG and glass based Faraday rotator rod was presented. These data will be useful for designing a laser system and a thermally compensated Faraday rotator.

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.

100 kW laser diode module for DPSSL fusion driver

High peak power laser diode arrays are required for pumping solid-state lasers as the laser fusion driver. We report successful achievement of a 100 kW peak power diode laser module as the pump source of 10 J/spl times/10 Hz Nd:glass slab laser in order to verify a small scale experiment of the diode-pumped solid-state laser (DPSSL) driver for inertial fusion energy development. The AlGaAs laser diode structures were grown by the MOCVD method and employed the quantum well structures.