A laser diode is the most common type of laser used and is formed from a semiconductor material. A semiconductor material, commonly used for creating parts in electronics, refers to a specific material that falls in the middle between a good conductor and a good insulator when it comes to conducting electricity. A diode simply refers to a device that lets electricity run through it in one direction and the laser diode uses this to emit the laser light the user sees. An electrical current is used to power the laser and is referred to as an injected electric current. The laser diode is also known as an injected laser diode or injection laser due to how the electric current used to power it passes through.
When the laser diode is created, a crystal is used and a thin layer of that crystal is purposefully altered to create an area that stays negatively charged and an area that stays positively charged. These areas are known as the n-type region and the p-type region, respectively. Together they form what is known as a p-n junction. The p-n junction forces electrical current passing over the crystal to be injected from both sides.
The n-type region and p-type region are both important because they allow both electrons and holes, a type of empty area from an electron which the electron will try to recombine with, to travel across the crystal to create the charge that powers the laser. Laser diodes work similarly to light-emitting diodes, more commonly referred to as LEDs. LEDs, however, are referred to as pumped laser diodes instead of injected laser diodes.
In an LED light, the electrons and holes recombine when the switch is turned on and the electrical charge is allowed to flow in one direction. When the electrons and the holes combine, they release energy as protons, which in turn light up the bulb. The light will be a different color depending on how much charge the photon has. Each colored LED light is designed to create photons that emit that specific color. A laser diode works in a similar fashion using electrons and holes to create a charge.
Most people have seen a laser diode in action if they have ever seen a bar code scanner in action. These scanners are commonly found at grocery stores and all bar code scanners use a laser diode to function. It creates the laser that passes over the black bars in the bar code. These black bars represent numbers, which the computer powering the cash register can interpret to identify the item being scanned.