Optical display: Laser diodes are used to project images or information onto screens or surfaces using devices such as projectors, TVs, monitors, and holograms. They emit beams of red, green, and blue light that combine to form different colors and shapes according to the input. A packaged laser diode shown with a penny for scale: a 488 nm InGaN green-blue laser, which became widely available in mid-2018. A laser diode with the case cut away. SEM (scanning. A laser diode (or diode laser) is a semiconductor device that undergoes stimulating emission to emit coherent light. These devices are capable of producing an intense laser ray with uniformly sized light waves.