Within only a few decades, the semiconductor laser diode has evolved into a family of robust, reliable devices, with individual conversion efficiencies of better than 60 percent, continuous output powers of several kilowatts, modulation rates of several tens of gigahertz . Within only a few decades, the semiconductor laser diode has evolved into a family of robust, reliable devices, with individual conversion efficiencies of better than 60 percent, continuous output powers of several kilowatts, modulation rates of several tens of gigahertz . 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. : 3 Driven by voltage, the doped. Semiconductor lasers are solid-state lasers based on semiconductor gain media, where optical amplification is usually achieved by stimulated emission at an interband transition under conditions of a high carrier density in the conduction band. 4. Laser diodes (LD) are semiconductor devices that convert electrical energy into high-power optical energy. Here, we present a ring-array quantum cascade laser (QCL). • A semiconductor laser diode is a device capable of producing a lasing action by applying a potential difference across a modified pn-junction. This modified pn-junction is heavily doped and contained within a cavity thus providing the gain medium for the laser.