How does stimulating emission occur in a laser?

Stimulated emission is a fundamental process in laser operation, where an incoming photon interacts with an excited electron in a metastable state. When this interaction occurs, the photon stimulates the electron to transition from a higher energy level to a lower energy level. As the electron falls to a lower energy state, it releases energy in the form of a second photon. This emitted photon has the same energy, phase, frequency, and direction as the incident photon, leading to the amplification of light, which is essential for laser operation.

In this process, the interaction is highly specific; it requires the electron to be in a state that can be stimulated by the photon. As a result, stimulated emission is a coherent process, meaning that all emitted photons are in phase with each other, which is a critical requirement for producing the coherent light output characteristic of lasers.

The other options do not accurately describe the process of stimulated emission, instead either referencing unrelated phenomena or omitting the critical role of photon interaction in the emission process.