A laser diode is a semiconductor-based PN junction device that converts electrical energy into coherent light energy through a process known as stimulated emission. It works on the same basic principle as an LED, but with an internal structure that forces photons to align in phase and direction, producing coherent laser light instead of the. A laser diode (LD, also injection laser diode or ILD or semiconductor laser or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction. Find out exactly how they work and what their advantages are in this guide.