Nobuto Kageyama

360-W average power operation with a single-stage diode-pumped Nd:YAG amplifier at a 1- kHz repetition rate

We report a high-average-power laser-diode-pumped Nd:YAG master oscillator power amplifier system that has a minimum number of elements in the single multipass zigzag-slab amplifier stage and is used to pump a high-peak-power and high-average-power Ti:sapphire laser system. This phase-conjugated system produces an average power of 362 W at 1 kHz in a 30-ns pulse with an optical-to-optical conversion efficiency of 14%. With an external KTP doubler this system generates 132 W of green average output power at 1 kHz with a conversion efficiency of 60% when pumped at a power level of 222 W. To the best of our knowledge these results represent the highest average output power at both infrared and green wavelengths achieved in a single amplifier stage.

Efficient and Reliable High-Power Laser Diode Bars With Low-Smile Implementation

We report on our recent development of high power 940 nm laser diodes (LDs) bars. The optimization of the laser structure and thermal management allow over 200-W continuous wave (CW) operation with 58% conversion efficiency from the 1-cm LD bar. We have also developed an assembly technique, and have suppressed the smile of LD bars mounted even on Cu heatsinks with hard solder to less than 1 μm. Long term stability have also be confirmed under 200-W CW operation.

200-W Operation of an Ion-Implanted Vertical-Cavity Surface-Emitting Laser Array

We have demonstrated a high-power 980-nm vertical-cavity surface-emitting laser diode (VCSEL) array with ion-implanted current apertures. The device was characterized on an exclusively developed water-cooled heat sink for the VCSEL array. A peak output power of over 200 W has been achieved under quasi-continuous-wave operation at a cooling water temperature of 10 °C. The VCSEL array consists of 635 emitters, which were defined by proton implantation and arranged in a closest packed arrangement with 175-μm-spacing in 5 mm × 5 mm square. The results provide a chance to the next step for a higher-power VCSEL array.

Design and Operation of High-Energy and High-Average-Power Diode-Pumped Single Nd:YAG Amplifier with Stimulated-Brillouion-Scattering Phase Conjugate Mirror

We describe a compact laser-diode-pumped, phase conjugate Nd:YAG master oscillator power amplifier system with a reduced number of components in the single slab amplifier geometry. This system is readily suited for pumping a Ti:sapphire amplifier, making it possible to construct a compact, high-repetition-rate, terawatt-peak-power chirped-pulse amplification system. An average infrared power of 362 W at a repetition rate of 1 kHz in a 29 ns pulse has been produced with an optical-to-optical efficiency of 14%. With a KTiOPO4 frequency-doubling crystal, an average green output power of 132 W at a repetition rate of 1 kHz has also been generated when pumped at an input incident power of 222 W, corresponding to a second-harmonic energy conversion efficiency of 60%. The average power at both infrared and green wavelengths represents a record performance for a single-amplifier system. We discuss in detail the design, performance and operation of the system including output power, optical efficiency, beam quality and stability.

Development of High-Power Quasi-CW Laser Bar Stacks With Enhanced Assembly Structure

We report on our recent development of quasi-continuous-wave 940-nm laser diode (LD) bars with passive cooled type. The 10 LD bar stacks with a narrow pitch of 1.54 mm have demonstrated a high output power of 10.1 kW, corresponding to 1 kW/bar, under 200-μs pulses at 50-Hz operating frequency. The maximum conversion efficiency of 58% has been achieved at an output power of 300 W. In condition of 1000 μs pulses at 10-Hz operating frequency, we have achieved an output power of 0.93 kW and a conversion efficiency of 59%, respectively. We consider that the LD bar stacks are suitable for diode pumped high-energy class solid-state lasers.

Developments of high-power 9xx-nm single emitter laser diodes and laser diode bars

We have developed the 915 nm single emitter LDs with a window structure. A high output power of 20.2 W and a power conversion efficiency of 66% at 10°C have been obtained without COMD. We have also developed the 940 nm LD bars using the thermal expansion controlled assembly technology. As a result, the smile has been successfully suppressed down to 0.7 μm. The power conversion efficiency is as high as 58% at output power of 200W, and the life test promises long-term reliability of the LD bars. The efficient and reliable high power operation of the LD bars with low smile has been compatibly achieved.

Numerical investigation of side emission from large-area vertical-cavity surface-emitting lasers

For large-area ion-implanted vertical-cavity surface-emitting lasers (VCSELs), side emission from the edges of a chip disturbs the laser emission of a VCSEL mode, and suppression of it is fundamental. In this paper, we present results of a numerical investigation of the side emission from large-area VCSELs. We have modeled a VCSEL structure by an infinitely broad layer structure with mirror loss at the edge surfaces. Estimated threshold gains indicate that laser emission occurs either in a VCSEL mode or in an edge-emitting Fabry-Perot (EEFP) mode. Calculated emitter length dependence of the threshold gain of these modes shows good agreement with experimental results, and the side emission is verified to be the laser emission of the EEFP mode. We have also discussed the way to suppress the side emission and confirmed that our recent achievement of over 200 W quasi-continuous-wave output from an ion-implanted VCSEL array is due to antireflection coatings of the edges and introduction of optical losses in ex-emitter regions.