The Evil Dwarf from Hell writes: "This weeks Science has an article on ZnO nanowire base UV lasers, abstract ( paid subscritption required for article). The 70 to 100 nm diameter wires lase at 386nm, line width .3 nm. The growth takes place on a thin Au film on a sapphire surface, and the wires reach lengths of 2 to 10 m. What makes this lasing unusual is it occurs without the use of mirrors. Apparently ZnO forms a natural lasing cavity. (The lasing is optically pumped from a Nd:YAG laser)." The link above is registration-required, but there's another article which describes the whole process.