Blue and red lasers are both typically made of a layered semiconductor that gives off photons. The light escapes from one edge of the thin chip, which makes it difficult to generate a bright beam. Scientists solved this problem for red lasers by creating many tiny lasers that shine from the flat surface of the chip. "The value of this type of laser is that it emits light in pixels," says Eric Tournié, a physicist with the Centre National de Recherche Scientifique near Valbonne, France.
Now a team led by Takao Someya of the University of Tokyo in Japan has duplicated the feat in blue. To create their laser array, the team first deposited a series of alternating layers--called a multilayer--of gallium nitride and aluminum nitride on a small sapphire chip. As they describe in tomorrow's issue of Science, the researchers then drilled with holes just 10 micrometers wide. After filling these cavities with semiconducting material, Someya and his crew capped the chip with another multilayer.
The semiconducting filling is blasted by another laser, whose photons have the necessary energy to create blue photons from the material. These blue photons bounce between the multilayers, producing other photons. Once enough are flying back and forth, photons begin to escape through the top layer and the laser is in action.
Because the blue laser's photons have a shorter wavelength than those in red lasers, they can detect much smaller pits or bumps in CDs or other storage media. And that means more music or information packed into a smaller space.