Imagine a bowling ball rolling down a flight of stairs covered with pudding. Upon hitting each step, it sends some pudding splattering. That's kind of what happens inside the new quantum-cascade semiconductor laser developed at AT&T Bell Laboratories--a laser that's fundamentally different from all previous ones.
Normally, lasers produce light from the collision of opposite charges--negative electrons annihilating positive particles, or "holes," in a flash of energy. But the new laser needs only electrons. The upshot: Its light can be easily changed for different jobs just by varying the thickness of the "pudding" on the microstairs inside its semiconductor crystal. As electron balls plop into the pudding, photons of light get kicked out. Their color depends on the pudding's thickness--and how much energy the electrons lost in getting through that layer of material. Bell Labs says the stair-step lasers should be ideal for jobs that require light beams to travel through air, including short-range communications and monitoring air pollution.