We have developed an ideal W‐class compact green laser for mobile projectors. The wall‐plug efficiency of the laser was higher than 15% over wide temperature range. By using RGB lasers and small LCOS projection optics, a mobile projector with high brightness (100 lm) and excellent efficiency (20 lm/W) was demonstrated.

By using air‐cooled RGB lasers including a compact and efficient green SHG laser and new illumination optics for speckle noise reduction, we developed advanced laser projection engine. A prototype of laser rear projection display with low electric consumption (about 50W) for light sources and wide color gamut (137%NTSC) was realized.

We proposed a multi-pass second harmonic generation scheme in which condensed fundamental light passed through a nonlinear crystal many times. The multi-pass scheme was realized by using a wide periodically-poled MgO:LiNbO3, concave mirrors and condensing optics. The total wavelength conversion efficiency of the multi-pass scheme was increased because non-converted fundamental light which had passed through the nonlinear crystal was re-injected and condensed into the nonlinear crystal and converted. Moreover the total temperature tolerance of the multi passes was widened because the fundamental beam passes had different phase-matching temperature and compensated for miss conversions of other passes. In this work, continuous-wave 5 W green light (532 nm) with 66% conversion efficiency and wide temperature tolerance were obtained.

Semiconducting donor (La)-doped barium titanate (BaTiO3) ceramics were synthesized at 1100•Ž in air by firing fine-grained crystalline gel powders of Ba-, La-, and Ti-alkoxides prepared by the sol-gel method. The ceramics showed resistivity of <103ƒ ¶•Ecm at room temperature with an average grain size of 0 .2-0.5ƒÊm, which was one order of magnitude smaller than that sintered from conventional powder oxides. Moreover, i n the La-doping concentration range of 0.2-0.7at%, BaTiO3 ceramics showed room temperature resistivity of <103ƒ ¶•Ecm, though the value of PTCR jump was small (about one order) because no acceptor-type ele ment was added. Early incorporation of La atoms in the BaTiO3 lattice during the sol-gel processes may con tribute to these results.

Highly-efficient fully air-cooled green laser light source with frequency doubling module is reported. As a result, 3.6 watts green laser light generation with about 9% wallplug efficiency is achieved. By using fully air-cooled RGB lasers including the green SHG (Second Harmonic Generation) laser and illumination optics for speckle noise reduction, a laser projection engine is prototyped. A laser rear-projection system with this laser projection engine shows several merits; wide color gamut (133%NTSC), 61inch large screen size, and low electric power consumption (less than 100W, at 650cd/mP 2 P ).