Japanese researchers have taken another step toward a compact ultraviolet light source that has great potential in high-density optical storage and biomedical applications. Scientists at Matsushita Electric Industrial Co.'s Development Center in Osaka, Japan, reported in Applied Physics Letters that they had frequency-doubled a 684-nm laser diode by directing it through a 150-µm-thick LiTaO₃ quasiphase-matching crystal. This produced 30 µW of ultraviolet light at 342 nm, with a conversion efficiency of 1.2 percent per watt.