The structure and the performance of super high power semiconductor lasers are reviewed. In 1987 1W laser which had a single broad area stripe with a 200μm width was introduced for applications such as solid-state laser pumping, medical instrument and machnning in industry. Since then, especially for solid-state laser pumping, various packages have been designed. For instance the package with a built-in TE cooler is used to raise pumping efficiency and the fiber module is used for mainely side pumping of laser rods. Alsopossibilities in getting much higher optical power have been pursued. One method is the broadening of stripe and the other is array; these methods respectively enabled the stable 3W and 10W laser.

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The high power characteristics of broad stripe gain-guiding quantum well lasers are reported. Graded-index separate confinement heterostructure (GRIN-SCH) -type quantum well lasers are grown on 0.5°misoriented (111) B GaAs substrates by molecular beam epitaxy. The reduction in the optical power density on the facet and in the driving current density is effective for increasing the maximum output power. The maximum output power of 3.7 W has been attained by small optical confinement in the graded-index waveguide region and by using a long cavity of 750μm.

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A broad-area AlGaAs SQW-SCH laser diode for side-pumping exhibits the maxmum outputpower of 2.6W in the absorption band of a Nd: YAG under CW conditions. Another broad-area laser diode with a modal reflector consisting of partially high-reflective coating for end-pumping operates at the maximum output-power of 0.4W under CW condtions with keeping the fundamental lateral mode.

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We succeeded in the phase locked operation of a 5-element GaAIAs diode laser array emitting 0.6W CW. The diodes use nonabsorbing mirrors (NAM's) for the suppression of catastrophic optical damage (COD) and a buried twin ridge substrate (BTRS) structure for the injection current confinement and for the stabilization of a transverse mode.

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This paper reviews the present status of research on surface emitting (SE) semiconductor lasers. There are four types of SE laser; vertical cavity, 45° mirror, grating coupled, and folded cavity. Lasing performances of these lasers are described and compared. Some characteristics of vertical cavity SE lasers are also summarized.

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This paper reviews the recent results on the short wavelength (λ′650nm) operation of our InGaAIP visible semiconductor lasers. Theoretically, the InGaAlP visible lasers with an Al-containing active layer should have a highly doped p-type cladding layer in order to reduce the threshold current. The room-temperature cw operation of this material is expected down to the 600nm. We experimentally achieved the room-temperature cw operation to 636nm, using a heter-obarrier blocking structure.

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A red semiconductor diode laser with a index-guided structure has been developed. A pair of SiO₂ film is located close to near the ridge stripe structure for the confinement of a lateral mode, and an n-GaAs current blocking layer are located outside the SiO₂ film for thermal diffusion. The astigmatism is very small, less than 6μm,

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An AlGaInP short wavelength laser diode with a tapered waveguide structure has been developed. Low power laser diodes with an emission wavelength near 670nm are under mass production for an optical source of a bar code scanner and a laser pointer.
A 630nm short wavelengh laser diode and a high power index guide laser diode are being developed.

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High-quality AlGaInP lavers lattice-matched to a GaAs substrate have successfully been grown by solid source MBE with a dimeric phosphorus beam. The bulk crystal quality and the abruptness of heterointerfaces were studided by measuring a photoluminescence spectrum. Net acceptor concentration in Be doped AlInP reaches saturation above -1×10¹⁸ cm^-3. A 10-μm wide stripe-geometry GaInP/AlInP laser diode is capable of stable CW operation at room temperature. The maximum output power of 12 mW was achieved.

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The characteristic crystal structure (natural superlattice) of AlGaInP grown by metal-organic vapor phase epitaxy (MOVPE) for the use of visible semiconductor lasers, material depends on the growth conditions. This paper descibes the dependence of the crystal structure and the effect on the device characteristics and device designing. In this connection, short wavelength laser operation and a novel laser structure for high power operation are also described (briefly).

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When an AlGaInP laser diode is grown on a GaAs substrate misoriented 5-7° to the <011> direction, the lasing wavelength of the diodes is shortened by about 20 nm compared with that of a diode using a (100) GaAs substrate. The diodes are grown by low pressure MOCVD. Using this technique, we obtained, for the first time, highly reliable AlGaInP laser diodes lasing at 567nm without adding Al to an active layer.

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High efficient frequency conversion of semiconductor lasers is necessary to obtain blue-green light for high dense optical memory, color display and so on. The principle for high effient frequency conversion and the properties of the promising inorganic materials such as KNbO₃, KTP and LiNbO₃ are described as well as newly developed organic materials. And the recently reported new techniques to get high conversion efficiency including external resonance cavity method, internal michrochip cavity method, quasi-phase matching method and so on are explained.

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The physical and optical properties of Neodymium doped single crystals for diode pumping laser are reviwed. Nd-doped lanthanum fluoride was grown and its primi ive properties were mesured.

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A laser diode-pumped solid-state laser has merits of compactness, high efficiency, long life, and easy maintenance. Nd: YAG is an excellent crystal for its large stimulated emission cross section and good thermal properties. The crystal shows good spectral matching with high power laser diodes. When used as a pump source, the its crystal growth and properties are described.

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Neodymium doped yittrium vanadate (Nd: YVO₄) single crystals were successfully grown from the stoichiometric melt by Chochralski's method. The effective distribution coefficient of Nd for Nd: YVO₄ growth was 0.57. As-grown crystals of undoped YVO₄ showed a slightly large and wide optical absorption at the short wavelength region near the absorption edge . However it was improved by an annealing at 1200° for 10 h in an oxygen atmosphere. The absorption by Nd³⁺ in Nd: YVO₄ was very strong compared with that in Nd: YAG of the same Nd concentration. The refractive indices of YVO₄ were also measured by a minimum deviation method. The principal refractive index at λ=1064nm (the main oscillating wavelength of a Nd: YVO₄ laser) was 1.9573 (ω) and 2.1652 (ε).

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Three types of LD pumped Nd: YAG laser are described. (1) In a “Lens focused LD end pumped Nd: YAG laser”, a cw laser output power of 290mW is obtained at an LD output power of 1.3W. (2) In an “LD directly coupled micro Nd YAG slab laser”, an LD beam is reflected at the upper and lower surfaces of a micro-slab, thereby bringing about excitation area small enough to give a TEM00 Nd: YAG laser beam. (3) In an “off-centered LD side pumped Nd: YAG laser”, a cw 1-W Nd: YAG laser beam of a stable output power is obtained at a pumping power of 8.4W.

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Using a “multiple-facet end-pumped” (MFEP) structure, we efficiently obtained high power from an LD-pumped Nd: YAG laser, the maximum output power of 5.4W at a pumping power of 16W. With an end-pumped structure, the second harmonic generation of Q-Switched Nd: YAG and Nd: YLF lasers with KTP, BBO, and LBO crystals is also described. The maximum average power of 110mW was obtained for the second harmonics of an Nd: YLF laser in BBO at a pumping power of 840mW.

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We have developed green, blue, and red solid state lasers by diode laser pumping. A green laseroutputs up to 22 mW at 531 nm with an NYAB crystal, and a blue one up to 7 mW at 473 nmwith Nd: YAG/KNbO₃ crystals. These visible lasers are efficient, compact, and reliable comparedwith flashlamp-pumped lasers or gas lasers. Many applications with these lasers arepresented.

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Having a larger stimulated emission cross section and stronger fluorescence emission, a laserdiode (LD) pumped Nd: YVO₄ laser has higher efficiency and power than Nd: YAG laser.Spectral property and CW end-pumped lasing characteristics have been measured on thismaterial. Stimulated emission cross section of 2.5×10^-18cm² for π polarization, slope efficiencyof 48.6% and light to light conversion efficiency of upto 40% for laser rod along a-axiswere obtained.

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The output properties of fundamental and second harmonic waves and the thermal properties of a Nd: YVO₄ microchip laser pumped by a laser diode were studied. The output power of 278mW at 1.064 μm was obtained with a pumping power of 730 mW at 808 nm, and the slope efficiencywas found to be 47.8%, The stable 0.53 μm light with an output power of 12.8 mW in asingle transverse and nearly single longitudinal mode was obtained by intra-cavity second harmonicgeneration using a KTP crystal of 7 mm in thickness. The temperature of the chip inoscillation was observed to be lower than that in the non-oscillating state.

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The potentiality of a laser diode pumped solid state laser system to drive a laser fusion reactoris described. The laser fusion reactor driver probably requires a few mega-joule output at thewavelength of 0.35μm, a 10 percent overall efficiency, and a 10 hertz repetition frequency. Using laser diode pumping and a regenerative amplifier, the solid-state laser system is shown tohave a sufficiently high efficiency (over 10 percent), long lifetime (over 3 years at 10 hertzoperation), and a high repetition frequency (over 10 hertz) owing to its small thermal load tolaser materials such as Nd: phosphate-glass, Nd: SiO₂, Ho: YAG, and Tm: YAG. Futureitems to be developed with the system are also discussed.

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Nd: YAG-laser-based materials processing has found remarkable acceptance inproductiontoday. Nd: YAG lasers are well suited to be incorporated to realize flexible manufacturing systems due to their flexibility in operation and variety in output performance. This paper brieflyreviews present activities to extend the fields of application for materials processing, such asmarking, trimming, welding and cutting with emphasis on the state of the arts ofthe advanced Nd: YAG lasers and various modern beam handling technologies.

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Semiconductor laser and diode-pumped solid state laser techniques are reviewed concerningremote sensing and precision instrumentation. First, the basic principles of remote range detectionusing these lasers are compared for a pulse method, intensity modulation method, randommodulation method, and frequency modulated (FM) heterodyne method. These methods are appliedto lidar (laser radar) for detecting the spatial distributions of atmospheric aerosolparticles. The FM heterodyne method is-capable of accurate measurement of both absolute rangeand displacement when widely tunable diode lasers are used. As potential applications ofdiode-pumped solid state lasers, a coherent lidar and a space lidar as well as an interferometerantenna of gravitational waves are introduced.

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Pulsed and CW semiconductor lasers have been applied following a He-Ne laser, tothe meticaltreatment of pains, inflammations, trophic ulcers and indolent wounds. Biological effects specificto lasers, wavelength, coherence, photoacoustic and electromagnetic effects, are briefly discussedwith regard to the biostimulative mechanisms of low level laser therapy.

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Looking into the worldwide laser device sales by application and the commerciallaser devicesales by laser types, we forecast a nearly 200% annual growth rate for laser-unitsales and dollarvolume by market of the leser diode (LD) pumped solid-state lasers. A futurcorrelation betweenLD laser diode or LD pumped solid lasers and other lasers in thenear-infrared, visibleand ultra-violet regions foresees that dye lasers and gas lasers will be replacedby LD and/or LDpumped solid-state lasers.

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