Takehito Nagakura

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.

High-Efficient and Reliable Broad-Area Laser Diodes With a Window Structure

We report on high-power 915-nm broad-area laser diodes with a window structure formed by a impurity-free vacancy disordering method. A maximum conversion efficiency of 68% and high output power of 19.8 W have been achieved at 20°C. A stable operation over 2000 h has also been confirmed under the condition of an output power of 15 W at 25°C. Far-field patterns suggest that the laser diode is suitable for coupling into an optical fiber with 105-μm core diameter and 0.15 numerical aperture.

Short-Pulse Operation of a High-Power-Density Proton-Implanted Vertical-Cavity Surface-Emitting Laser Array

We report on a GaAs-based high-power-density vertical-cavity surface-emitting laser diode (VCSEL) array with ion-implanted isolated current apertures. A peak output power of 40.6 W has been achieved from the VCSEL array with seven emitters under 100-ns-pulse operation. This is the first demonstration of a ten-watt-class output power for a VCSEL array with ion-implanted isolated current aperture configuration. The corresponding power-density is estimated to be 73.8 kW/cm2, which is three times greater than the record power-density of the short-pulse-operated oxide-confined VCSEL.

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.

Study on propagation characteristics of a high-powered multi-quantum-well (MQW) LD beam

The beam propagation properties of the high-powered Multi-Quantum-Well (MQW) laser diode (LD) are definitive elements in many application fields such as micro-processing, biomedical technique, and basic research, etc. In this study, the beam characteristics of a high-powered InGaAs/AlGaAs MQW-LD have been evaluated in both fast-axis and slow-axis. The multi-planar waveguide model and the non-paraxial second-order moment theory were used in analyses of the beam propagation features in the direction perpendicular to the active layer of a MQW-LD. The experimental results of the beam character measurement accord with those of the theoretical calculation very well for a sampled InGaAs/AlGaAs MQW-LD. The analysis approach is thought to be useful for design of the LDs and the other waveguiding optical devices.

Long-Term Reliability of 915-nm Broad-Area Laser Diodes Under 20-W CW Operation

We report on the long-term reliable continuous wave (CW) operation of high-power and high-efficiency 915-nm broad-area laser diodes (BA-LDs). An output power of over 20 W and a maximum power-conversion efficiency of over 65% have been marked at a heat-sink temperature of 20 °C. Stable operations of over 5000 h have also been achieved for the 915-nm and 976-nm BA-LDs with CW output powers of 20 W, respectively. The window structure with a bandgap difference of 100 meV provides the reliable operation at the high-output power range.

Development of a high-power vertical-cavity surface-emitting laser array with ion-implanted current apertures

Vertical-Cavity Surface-Emitting Lasers (VCSELs) are very attractive to high power light sources owing to the advantageous configuration of two-dimensional arrays and being free from catastrophic optical damage. Although oxideconfined VCSELs have been employed in most of applications with VCSELs, ion-implanted VCSELs have a potential to be the better light sources for high power applications. In spite of the fact, the detailed characteristics of the ionimplanted VCSELs had been researched only in ten milliwatt-class output power. Here we report on a high power VCSEL-array with proton-implanted current apertures. A peak output power of over 40 W under short-pulse operation has been achieved. This is the first demonstration of ten watt-class output power for ion-implanted VCSELs.

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.

High-power and high-efficiency 915 nm broad-area laser diodes with window structure

This paper presents high-power high-efficiency 915 nm broad-area laser diodes with the window structure fabricated using optimized impurity-free vacancy disordering (IFVD) process.