Laser-driven inertial confi nement fusion (laser fusion) has been investigated with large-scale high-power lasers since 1960’s. Progress of new laser technology, such as multi-beam irradiation system, frequency conversion, beam smoothing, and chirped pulse amplifi cation, signifi cantly accelerated the laser fusion research. FIREX project to demonstrate efficient heating of the compressed fuel to the ignition temperature with Fast Ignition scheme is underway in Osaka. Attempt to achieve high-density implosion and ignition is also underway on NIF in the US, and the first demonstration of the thermo nuclear ignition and burning of controlled nuclear fusion will be demonstrated soon by laser fusion. Laser fusion demo power plants are expected to appear in 2020‒2030. Laser drivers with large output energy, high effi ciency, high repetition rate, long life, and low cost will be required for laser fusion reactors.

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This paper describes the past and the present status as well as the future prospects of red, high power laser diodes (LDs) for smart laser displays and concentrates on broad area LDs (BA-LDs) that include arrays and narrow stripe LDs (NS-LDs). Since luminosity increases as the wavelength shortens in the red region, LDs are designed to emit around 640 nm. The output of the state-of-the-art BA-LD, which exceeds 14 mW/μm with 638-nm wavelength and wall plug efficiency (WPE) of 35%, shows stable operation up to 8000 hours. NS-LD provides 150-mW output with 642-nm with a WPE of 21%. LDs might be improved for higher output with greater high wall plug effi ciency.

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GaN-based blue laser diodes (LDs) are expected to be adopted to the light sources for full color laser display systems. In this paper, the status of blue LDs development is reviewed, and new high-power blue LDs on c-plane GaN substrate, which were recently fabricated, are disclosed. The typical optical output power, voltage and wall-plug efficiency at an operating current of 2.3 A, for these LDs, were 3.75 W, 4.24 V, and 38.5%, respectively. The lifetime estimated from 50 ℃ aging test was over 30,000 hours.

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Continuous-wave operation of InGaN green laser diodes (LDs) on semi-polar {202 －1} GaN substrates with output powers of over 100 mW in the spectral region beyond 530 nm is demonstrated. Wall plug efficiencies (WPEs) as high as 7.0 ‒ 8.9% are realized in the wavelength range of 525 ‒ 532 nm, which exceed those reported for c-plane LDs. The difference in the WPEs between these two crystal orientations was found to become larger with increasing wavelength. These results suggest that the InGaN green LDs on the {202 －1} plane are better suited as light sources for applications requiring wavelengths over 525 nm. We also discuss the current status and the future prospects on the output power and the lasing wavelength of green semiconductor LDs compared with c-plane LDs.

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Laser diodes in the yellow spectral region are important as compact and highly-efficient light sources for displays and measurements. Conventional III-V or III-nitride semiconductors are thought to have difficulty in realizing a laser diode of this spectral region. We demonstrated the continuous-wave operation of semiconductor laser diodes in the green-to-yellow spectral region with BeZnCdSe quantumwells. The lasing wavelength of the fabricated yellow laser diode was 570 nm. The light output power was as high as 50 mW with a low threshold current density.

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Increasing the reliable operation power of laser diodes enables a wide range of telecom and industrial applications. In this paper, such high power laser diode technologies as the suppression of catastrophic optical damage, improved effi ciency, and increased emitters are reviewed. Developed high power laser diode products are also discussed. For 9xx nm laser diodes, we present 15-W reliable operation from a 95 μm wide emitter and 60-W operation from a mini-bar with 7 emitters and 100 μm emitter width.

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During the last decade, the development of Mid-IR (4～11 μm) Quantum Cascade Lasers (QCLs) has shown substantial progress toward to the commercial availability of such devices. In developing newly high performance QCLs, we focused on high-power QCLs for bio-medical applications, and developed a Fabry-Perot (FP-) type QCL emitting at the 6-μm (～1700-cm‒1) wavelength range. This wavelength range is expected to be absorbed by organic matter. The active region structure of QCL is based on InGaAs/InAlAs super lattice grown by MOCVD. High refl ection coated FP-QCL chip is mounted episide down on the Cu heat-sink. The average output power exceeds 1.1-W in pulsed operation (dutycycle 50%) at 20 ℃. High-power QCLs show good potential for less-invasive and selective laser surgery.

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By way of bandgap engineering, optically pumped semiconductor lasers (OPSLs) can be made to operate at tailored wavelengths, giving access to broad spectral regions, extending from visible (red) to infrared, fi lling wavelengths that were previously not accessible with solid-state laser materials. With the free space resonator confi guration, OPSLs feature good beam quality with its scalability in output power. Free space resonator also allows intracavity frequency doubling for effi cient harmonic generation, further extending the wavelength to the shorter end. Nonlinear frequency conversion gives complete coverage of visible region and extends into the ultraviolet portion of the spectrum. The potential of OPSLs is explored toward the high power devices, short pulse generation, as well as their application in spectroscopic applications.

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