Which of the following processes occurs in a laser diode?

In a laser diode, stimulated emission is the fundamental process that enables the generation of coherent light. In simple terms, stimulated emission occurs when an incoming photon interacts with an excited electron in a semiconductor material, causing the electron to drop to a lower energy level. During this transition, the electron emits a photon that has the same phase, frequency, and direction as the incoming photon. This results in the amplification of light, a key characteristic of laser operation.

The presence of a population inversion, where more electrons are in an excited state than in a lower energy state, is essential for stimulated emission to dominate over other processes. This condition is achieved in laser diodes through the injection of electrical current, which energizes the electrons.

While spontaneous emission can also occur in a laser diode (and may contribute to the initial generation of light), it does not lead to the coherent and amplified output characteristic of laser light. Thermal emission and photoemission do not play significant roles in the functioning of a laser diode; the first relates to the emission of electrons due to thermal energy, while the latter involves the emission of electrons as a result of absorption of light rather than the coherent light generation central to laser operation. Therefore, stimulated emission is the process that primarily defines the function