A laser diode is a semiconductor device that emits light when an electric current passes through it. It works by using a process called electroluminescence, where electrons recombine with holes in the semiconductor material, releasing energy in the form of light. Laser diodes are compact, efficient, and can produce coherent light, which means the light waves are in phase and can travel long distances without spreading out. These devices are commonly used in various applications, including optical communication, laser printers, and barcode scanners. Their small size and ability to generate focused beams make them ideal for technologies that require precise light sources.