For the first time ever, superfluorescence has been observed in a solid-state material. Previously this phenomenon had only been seen in molecular and atomic gases. As the name suggests, superfluorescence has to do with an extraordinary emission of light. Given the proper circumstances, a material’s electrons can be excited and collectively fall back to lower energies, releasing photons in a single, great pulse. Researchers at Rice University have successfully gotten this to occur in a material with 15 quantum wells stacked on top of each other, with gallium arsenide (GaAs) layers in between. Gallium arsenide is a semiconductor which will transfer the energy of an incoming photon to an electron.
With a sufficiently powerful, and fast, laser pulse, the electrons of the GaAs were excited. When electrons are excited into the conduction band, they leave bind holes where they had been. There were enough electron-hole pairs to form a magneto-plasma, and initially there was no pattern to the plasma. Before long though, the pairs lined up and started falling into the quantum wells where the pairs would recombine and release a photon. The photons then travel through the stack causing a macroscopic coherence of all photon emissions. Essentially, the laser pulse that energizes the system is like a potential energizing a capacitor. Eventually the energy in the capacitor is released all at once.
There are several mysteries surrounding this experiment though. For example, the frequency of the emitted light is related to the time it is released. Also, there were distinct peaks in time for the superfluorescent emission. Of course, what’s the fun of answering one question without thinking of a few more to ask?