Substantial progress has been made overseas in diode-pumped solid-state lasers during these 10 years since the emergence of a high-power diode arrays in mid-eighties. Recently, the CW output power at 1.06 μm has exceeded 300 W in a multimode-operation and the CW power of 20 W has been obtained in a single frequency operation. A high-beam-quality, 1 kW high average power, repetitively pulsed laser system is also being developed. This article reviews recent progress in high-power diode-pumped solid state lasers in the world, including Q-switched lasers, with particular interest in their industrial applications, such as laser materials processing.

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Compact solid state lasers with high repetition rates and high average power are strongly desired as the pumping sources for both tunable lasers in selective laser chemistry applications and ultra-short pulse lasers in compact x-ray laser development. Japan Atomic Energy Research Institute has conducted the development of laser diode pumped solid state lasers by taking into account high thermal load in the solid optical components, and accomplished 19W green power at a repetition rate of 1kHz by EO-Q switching and 6.3W fundamental power at a repetition rate of 10kHz by AO-Q switching.

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Recent progress in high power laser diodes and 2-dimensional high power laser LD arrays is reviewed. We have developed 0.8-0.9 μm band high power LD arrays for pumping solid state lasers and evaluated their characteristics. With 10-stack LD arrays, 750W peak power was obtained under the quasi-CW conditions.

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The present status of the measurement of thermal birefringence and its compensation in laser-diode (LD) pumped Nd:glass laser rods is reviewed. To measure the two-dimensional (2D) thermal birefringence in solid-state laser materials such as Nd:glass (HAP4) a high-sensitivity polarimeter is introduced.This polarimeter can sensitively measure the direction of the principal birefringence axis as well as the phase shift δ with sign when δ < π/4. The 2D thermal birefringence and its compensation in a LD pumped Nd:glass (HAP4) rods are successfully measured with this polarimeter. The birefringence compensation is reported by inserting a 90° rotator between two identical LD pumped Nd:glass rods with conduction cooling. The birefringence loss due to this thermal birefringence in a polarized laser cavity can be estimated by using Jones matrix. A considerable reduction of birefringence loss from 9.8% to less than 0.9% after compensation is performed.

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The excited-state absorption (ESA) and tuning characteristics of a solid-state gain medium Ce3+:LiSrAlF6 (Ce:LiSAF) has been studied. The VUV absorption edge which contributes to the ESA was found at 135 nm. The difference between the 290 nm and 310 nm gain bands was shown in an upper state fluorescence lifetime at 120 K. A slope efficiency of 24 % with an output energy of 2 mJ was achieved in the side pump configuration. Tunable oscillation was demonstrated in the range of 285 to 295 nm.

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A simple design method for longitudinally diodepumped solid-state lasers has been studied. The study indicates that the requirements of the focusing optics of the pump source to realize highly efficient. The desighn method was achieved by using an M2 factor to describe the multi-transverse mode beam of broad area diode lasers and was examined by using a diode pumped Nd:YVO4 miniature laser. A good agreement was obtained between theoretical and experimental output results. A low-threshold and 58.0 % slope efficiency laser oscillation were realized with circular output beam.

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We propose a novel high efficient diode-side-pumping configuration of a solid-state laser. The optical slope efficiency of 52.2% was proved in a continuous-wave mode, an efficiency which is, to our knowledge, the highest for diode-side-pumped Nd:YAG rod lasers. The electrical-to-optical slope efficiency was 30.3%. With a diode output power of 135.1W and an electrical input power of 327.3W into diode arrays, we obtained a multi-mode output power of 40.0W which corresponds to a total optical efficiency of 29.6% and a total electrical-to-optical efficiency of 12.2%.

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We describe a simple-design laser-diode-pumped CW Nd:YAG active-mirror laser and a thermal analysis in the crystal. A CW output power of 2.4 W and an M2 beam-quality value of less than 1.9 at an incident pumping power of 8.9 W have been obtained. From the thermal analysis, we predict that the output power can be increased by increasing the pump beam diameter at a constant pump-power density. We also calculate the maximum temperature rises and the focal lengths of thermal lenses for various cylindrical laser crystals with different radius-to-length aspect ratios.

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GaAs/AlGaAs high-power semiconductor laser diodes are widely used for optical data storage disks such as magneto-optical disks, mini disks, and phase-change disks. Improvement of the characteristics of high-power lasers is indispensable to achieve excellent performance of optical disks. The present paper reviews several laser structures developed to attain a high output power for high-speed data transferring in optical disks. Also reviewed are various laser structures developed to attain a low driving current and a low noise for low power operation and RF-module free pickups in optical disks.

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This paper proposes a new high-speed method for computer-generated hologram (CGH) and virtual image reconstruction. The time for calculation of CGH is reduced by 42 times less than the ray-tracing conventional method, with similar resolution, applied to a circle model as an object. Combined with the correlation method in reconstruction, the computational time is reduced by 48 times less than the original idea of the correlation method, with much better virtual image than FFT method, applied to the same circle model. The new method is described and examined by different object models.

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We propose and confirm a novel techniqe of optical frequency domain reflectometry based on the detecton of an interference spectrum by using a multi-mode laser. The proposed systems composed of a free-running laser diode, an optical spectrometer and a computing system for FFT can easily provide the potential for ultrahigh resolution on the order of 10 μm without scanning frequencies as in frequency domein refletometers of either the continuously or the stepwise-swept variety.

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We propose and confirm a novel optical frequency domain reflectometry based on the phase sensitive detection of an interference specrum by using a multi-mode laser as a source. The main advantage of this method is its high sensitivity because of the phase sensitive detection of only an interference spectrum signal component. As a result, the dynamic range of the measurement can be improved. The experimental data show that this method is more sensitive than direct detection methods of interference spectra.

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In this paper, characteristics of amplitude modulated harmonically mode locked (AM-HML) erbium doped fiber (EDF) ring laser are presented. It is investigated that the AM-HML method can provide a precise control of the lasing spectral bandwidth. Which in turn, can control the nonlinear effects in single mode fibers, such as stimulated Brillouin scattering in optical fiber communications. The optical spectral bandwidth is found to be broadened from -5GHz to-16.6GHz when the AM modulating low harmonic signal frequency is varied from -3.1609MHz to -44.2526MHz (1 to 14 times of the fundamental cavity frequency fa) at a fixed pulse rate of fh 2.1241 GHz. The effect of the percentage of AM modulation depth is also studied and it is observed that the bandwidth of the AM-HML laser is slightly affected when the percentage of AM modulation is varied from -5% to -50%.

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