Tiny, levitating semiconductor particles can produce laser light. This happened when a group of researchers led by Lijun Wang at the University of Erlangen in Germany encased quantum dots with cadmium-selenide cores and zinc-sulphide shells in microdroplets of water and glycerine, and electrically charged the droplets to keep them floating in air. When energized with light from a laser, the encased quantum dots generated their own laser light.
A microdroplet forms a super-smooth spherical capsule around the quantum dots, causing the photons they give off to oscillate at specific wavelengths, a requirement for lasing. Surprisingly, the density of quantum dots within a single microdroplet needed to produce laser light was very low, the researchers say — as was the power needed to drive the process.