Takeshi Kanzaki

Design and Performance of a Diode-Pumped Nd:Silica-Phosphate Glass Zig-Zag Slab Laser Amplifier for Inertial Fusion Energy

A high-energy, high beam quality, diode-pumped 1053-nm Nd:silica-phosphate glass laser amplifier has been designed, constructed and tested in order to verify the conceptual design of HALNA (high average-power laser for nuclear-fusion application): a diode-pumped solid-state laser based on a water-cooled zig-zag slab optical geometry. This amplifier yields an 8.5 J output energy per pulse at 0.5 Hz in a 20 ns pulse of two times the diffraction limit beam quality with an optical-to-optical conversion efficiency of 10.9%. This is the first demonstration of a diode-pumped solid-state laser amplifier for the inertial fusion energy (IFE) driver. The detailed considerations on the optical and thermal designs of the novel amplifier architecture are discussed. The experimental results revealed that the primary requirements for the IFE driver, such as diode-pumping, energy storage and extraction efficiencies, and beam quality have been fulfilled.

Jet-type, water-cooled heat sink that yields 255-W continuous-wave laser output at 808 nm from a 1-cm laser diode bar

A newly designed jet-type, water-cooled heat sink (the funryu heat sink, meaning fountain flow in Japanese) yielded 255-W cw laser output at 808 nm from a 1-cm bar made from InGaAsP/InGaP quantum-well active layers with a 67% fill factor [70 quantum-well laser diode (LD) array along the 1-cm bar]. A funryu heat sink measuring 1.1 mm in thickness gave the LD 0.25 degrees C/W thermal resistance, one of the lowest values achieved with a 1-cm LD bar. Over a short period of operation, the device reached a maximum cw power of 255 W. To the best of our knowledge, this is the highest power ever achieved in 808-nm LD operation. In the future, the funryu heat sink may be capable of 80-W cw operation over an extended lifetime of several thousand hours.

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.

Quasi-CW 110 kW AlGaAs Laser Diode Array Module for Inertial Fusion Energy Laser Driver

We have successfully demonstrated a large aperture 803 nm AlGaAs diode laser module as a pump source for a 1053 nm, 10 J output Nd:glass slab laser amplifier for diode-pumped solid-state laser (DPSSL) fusion driver. Detailed performance results of the laser diode module are presented, including bar package and stack configuration, and their thermal design and analysis. A sufficiently low thermal impedance of the stack was realized by combining backplane liquid cooling configuration with modular bar package architecture. Total peak power of 110 kW and electrical to optical conversion efficiency of 46% were obtained from the module consisting of a total of 1000 laser diode bars. A peak intensity of 2.6 kW/cm2 was accomplished across an emitting area of 418 mm×10 mm. Currently, this laser diode array module with a large two-dimensional aperture is, to our knowledge, the only operational pump source for the high output energy DPSSL.

Laser-diode-pumped 10-J X 10-Hz Nd:glass slab laser system

As a first step of a driver development for the inertial fusion energy, we are developing a diode-pumped zig-zag Nd:glass slab laser amplifier system which can generate an output 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 200 kW peak power with 2.5 kW/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 100-kW laser diode module for 10-J x 10-Hz Nd:glass slab laser

High peak power laser diode arrays are required for pumping solid-state lasers toward the laser fusion driver. We will present a first successful achievement of a 100 kW peak power AlGaAs diode laser module as the pump source of 10 J X 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 total peak power of 110 kW was obtained at the diode current 120 A, the pulse width 200 microsecond and the duty cycle 0.2% (10 Hz). The peak intensity was more than 2.5 kW/cm2 on the average over the emitting area of 418 mm X 10 mm. The center wavelength of this device was 803 nm at the cooling water temperature 17 degrees Celsius, which designed in order to fit within the peak absorption line of Nd:glass (HAP-4) slab.

Laser-diode-pumped eight-pass 100-W-class Nd:YAG zig-zag slab laser amplifier

A novel laser architecture of laser-diode pumped eight pass 1064-nm Nd:YAG zig-zag slab laser amplifier with thermal birefringence compensation by use of a 90 degree quartz rotator has been developed aiming to achieve a high average power laser with high efficiency and good beam quality. With a 100 W (1 kHz) class module, the basic performance of the novel concept was examined by demonstrating an average power of 68 W with a high energy extraction efficiency of 61% for the laser mode volume at an initial small signal gain of 3.03 on single pass, and an excellent beam quality, undernegligible thermal lensing with the compensation for thermal birefringence.

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.

Development of high-power DPSSL 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 for 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 a 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.