In 1946 Edward Purcell proposed that the spontaneous emission from the excited state of an atom could be changed significantly by placing the atom in a cavity with dimensions similar to the wavelength of the emitted light. This idea was subsequently confirmed in many experiments and has since been used as the basis for many types of microlaser. Now Axel Scherer and co-workers at the California Institute of Technology and the University of Southern California have built such a laser in a two-dimensional photonic crystal (Science 284 1819).
The photonic crystal was made by using an ion beam to drill a 2D hexagonal array of holes in a layer of indium gallium arsenide phosphide (InGaAsP). The regular spacing of the holes means that only certain wavelengths of light can propagate in the crystal. The holes were 515 nm apart and had a radius of about 180 nm. The crystal was prepared such that one of the holes was “missing” – this defect provided the laser cavity for the device. Photons are trapped in the defect, which is only 0.03 cubic micrometers in size. When cooled to 143 Kelvin, the device emitted pulses of laser radiation with a wavelength of 1.5 microns.
