Gain in blue lasers
The gain of a blue laser diode when pumped by a laser was measured as a function of photon energy. When the power density of the pump laser was greater than 1 MW cm-2, a sharp peak was observed in the gain at 3.06 eV. The results indicate that absorption by excitons in the n = 1 energy level transfers electrons into localized states, and that stimulated emission is taking place between these states and the valence band of the active layer.