A laser diode (or diode laser) is a semiconductor device that undergoes stimulating emission to emit coherent light. 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. The laser diode chip is the small black chip at the front; a photodiode at the back is used to control output power. SEM (scanning electron microscope) image of a commercial laser diode with its case and window cut away. These gadgets track down wide applications because of their proficiency and minimal size. This article discusses the characteristics common to laser.