 down an energy "staircase," and every time an electron hits a step, a photon of infrared light is emitted. The emitted photons are reflected back and forth inside the semiconductor resonator that contains the electronic cascade, stimulating the emission of other photons. This amplification process enables high-output power from a small device. In the decade since their invention, QC lasers have proven to be very con- venient light sources. Besides being powerful, they are compact, rugged, and often portable. Yet the devices can't emit light from its edges or through its surface. The Bell Labs team overcame this challenge by using the precise light- controlling qualities of a photonic crystal to create a QC laser that emits photons perpendicular to the semiconductor layers, resulting in a laser that emits light through its surface. Photonic crystals are materials with repeating patterns spaced very close to one another, with separations between the pat- terns comparable to the wavelengths of light. When light falls on such a pat- terned material, the photons of light interact with it; with proper design of the patterns, it's possible to control and manipulate the propagation of light within the material. Using a state-of-the-art electron beam lithography facility at the New Jersey Nanotechnology Consortium, located at Bell Labs headquarters in Murray LIGHT EMITTERS Hill, New Jersey, the researchers were able to superimpose a hexagonal pho- tonic crystal pattern on the semiconductor layers that made the QC laser. The final laser was only 50 um across or about half the diameter of a human hair. "The most exciting part of this work is that we combined photonic and elec- tronic engineering to create a new surface-emitting QC laser," says Al Cho, adjunct vice president of semiconductor research at Bell Labs and one of the inventors of the QC laser. "The photonic crystal approach has real potential for new applications. The production of surface-emitting compact lasers only 50 micrometers across enables large arrays of