What is the principle of how lasers produce light?

Lasers operate on the principle of stimulated emission of radiation, which is central to their functionality. This process begins when an excited atom or molecule—having been energized—encounters a photon. When this photon interacts with the excited atom, it can stimulate the emission of a second photon that has the same energy, phase, and direction as the first. This creates a coherent beam of light as the newly emitted photons propagate through the laser medium.

This stimulated emission is vital for the amplification of light within the laser cavity. The setup typically includes mirrors to reflect the photons back and forth, allowing multiple rounds of stimulated emission to occur, which amplifies the light output significantly. Consequently, the coherence, monochromaticity, and directionality of the produced laser light stem directly from this principle.

The other processes mentioned, such as electromagnetic induction, photon absorption, and thermal radiation, do not relate to the core mechanism of a laser's operation. Electromagnetic induction involves generating electric currents using a changing magnetic field, which is unrelated to light production in lasers. Photon absorption refers to the energy exchange where photons are absorbed by atoms, raising them to an excited state but does not lead to light emission like stimulated emission does. Thermal radiation involves the emission of light from a