Laser display has been attractive because extremely wide color expression can be realized by choosing the wavelength of laser sources. The highly efficiency and small etendue of laser sources contribute to downsizing, and long lifetime is also another merit for users. High power and compact red, green, and blue (RGB) lasers have been expected to realize the practical laser display. In this paper, highly efficient RGB lasers based on laser diodes and second harmonic generation devices are introduced. Also laser display systems by using these lasers are discussed.

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A potential of high-power pure blue GaN-based semiconductor laser was evaluated. A maximum output power was estimated to be 0.8 W by using 10-μm-wide single stripe geometry. However, according to a theoretical prediction, a lifetime of this device at RT was found to be very short, i. e. it is only 1000 h under O.14 W-operation. This short lifetime may be attributed to the partial degradation of active layer around the threading dislocations. Further improvement of GaN substrate, which is used as a template of device structure, is necessary to realize highly reliable high-power pure blue semiconductor lasers for laser display applications.

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We review the recent trends of visible light sources based on nonlinear frequency conversion from the Nd³⁺-doped micro-lasers. In order to evaluate the emission properties of 1.3, 1.0, and 0.9 in Nd³⁺-ion doped materials, the spectroscopic parameters were summarized. Recently appeared Nd: GdV₄O has the large absorption and emission cross-sections with high thermal conductivity, as high as YAG. After the demonstration of near quantum limit highly efficient operation in Nd: GdVO₄, the intra-cavity frequency doubled micro-laser was reviewed as a high power compact green laser. On the other hand, we have demonstrated the high power stable green and deep blue laser under extra-cavity frequency doubling with periodically-poled MgO: LiNbO₃ (PPMgLN) for quasi-phase matched second harmonic generation (QPM-SHG). Finally, edge pumped Yb: YAG microchip laser was discussed for the high-power visible microchip lasers.

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Red high power semiconductor lasers are expected to be used as a light source of laser projection display systems. The characteristics of these lasers need to satisfy several demands in such display system: high power operation for brightness, long device lifetime for high reliability of systems and uniform near field pattern for good uniformity of display. We have achieved 7 W operation of red semiconductor array lasers with high reliability at a wavelength of 643 nm for the first time. The uniform near field pattern has been obtained by applying an index-guided structure for broad-stripe laser. The bending of the array laser is controlled to be smaller than 21μm, which will lead to high resolution of display.

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Red, green, and blue, the three primary colors, are essential for laser-based color displays that take advantage of the high brightness, spectral purity and extremely large depth of focus of laser sources. There remains a problem as how to generate laser radiation in these colors in a single compact laser system in order to reduce cost, size and to obtain potential integration. Recently many attempts have been made towards this goal. In the as-grown crystals of LiNbO₃ and SBN, the domain structures are formed spontaneously during the crystal growth process, resulting in very low conversion efficiency. Our study showed that with a careful design of the domain engineering, efficient RGB light generateon can be realized by coupled quasi-phase matching method. A brief review will be given in this field.

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We have developed efficient SHG devices for green and blue light generation with periodically poled structures in thick Z-cut MgO: LiNbO₃ utilizing a multi-pulse poling method. Uniformly periodically domaininverted structures with a period of 6.95μm and 4.19μm were fabricated over 10-mm interaction length. We have demonstrated highly efficient green and blue light generation using bulk QPM-SHG devices with this structure. Using compact and high-power Nd: GdVO₄ micro-laser, CW SHG of 1.03W at a wavelength of 531nm was generated with conversion efficiency of 16.5% by single-pass configuration at room temperature. Moreover, CW SHG of 167mW at a wavelength of 456nm was realized with a conversion efficiency of 8.3%.

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Antireflection (AR) coating with high damage resistance for optical guides of high power YAG laser was developed. We have indicated that each single layer films must be improved AR coating with high damage threshold. An optimum deposition of the Si0₂ film and Ta₂O₅ films that compose the AR coating was studied by the Taguchi method. Reflectance and laser-induced damage threshold of AR coating was less than 0.2% and 15.9 J/cm², respectively at 1064 nm. The AR coating irradiated by cw YAG laser of 3-kW class was durable for 5 minutes.

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Optical damage to the surface of the ruby crystal rod in a Q-switched high-energy ruby laser for medical uses is analyzed, and a method to suppress the optical damage is successfully implemented.

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Areal-time monitoring method that simultaneously measures hole depth during femtosecond laser processing has been developed. It measures and analyzes the interference between reflected pulses from sample material and prepared reference pulses in a Mach-Zehnder interferometer. Since femtosecond laser light has broad spectrum, measurement depth resolution achieves accuracy as high as 5.5 micrometers. We applied the method to acrylic resin microdrilling and succeeded in real-time depth measurement. It was also proved experimentally that this new method measured hole depth having high aspect ratio because it was in a situ measurement. This real-time hole depth measurement is expected to be a powerful and useful tool for femtosecond laser material processing.

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Generation of efficient frequency-double fiber-based continuous wave (cw) orange laser radiation at 590-nm by single-pass second harmonic generation (SHG) of 1180-nm high-power Raman fiber laser in two 20-mm long bulk periodically poled MgO doped lithium niobate (PP-MgO: LN) crystals arranged in series is reported. Single-pass SHG efficiency with a single 20-mm long crystal was limited by large linewidth of the fundamental laser source in comparison to the wavelength acceptance of the PP-MgO: LN crystal. With this configuration, 50-75% increase in SHG efficiency has been obtained. At 9.9-W of the 1180-nm Raman fiber laser, 1.2-W of cw orange laser radiation with power stability of ±1.2% recorded over a one-hour period has been achieved.

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