Which of the following is an example of a diode laser active medium?

In the context of diode lasers, the active medium refers to the material used to produce the laser light through the process of stimulated emission of radiation. Indium Gallium Arsenide (InGaAs) is a common choice in semiconductor laser technology, particularly within the near-infrared region of the spectrum.

InGaAs is specifically advantageous for its direct bandgap properties, which allow efficient light emission when an electrical current excites the electrons in the crystal lattice. This quality makes it well-suited for applications in fiber optic communications, as well as in laser diodes used in various medical and industrial settings.

Other materials listed, like GaAs (Gallium Arsenide), AlGaN (Aluminum Gallium Nitride), and SiN (Silicon Nitride), have their specific applications but do not serve as the prominent active medium in diode lasers as InGaAs does. For instance, GaAs is often used but primarily combines with others in multi-layer structures for specific functionalities rather than standalone use. AlGaN is used for ultraviolet lasers, and SiN is not typically an active medium in laser applications but rather a dielectric or passivation layer in various semiconductor devices.