What is the principle of laser operation?

The principle of laser operation is based on stimulated emission of radiation, which is the process that generates coherent light. In a laser, atoms or molecules are excited to a higher energy state, usually through pumping energy into the system, such as through electrical or optical means. When these excited atoms return to their lower energy state, they can emit photons.

In stimulated emission, an incoming photon of a specific energy interacts with an excited atom, causing it to release another photon that is identical in phase, frequency, direction, and polarization. This results in a cascade effect, where one photon stimulates the release of more photons that are all coherent with one another. The coherence of the light produced by a laser is a defining characteristic; it allows the light to be focused into a very narrow beam and travel long distances with minimal divergence.

The other options refer to different processes of light generation that do not create coherent light or operate based on the same mechanisms as lasers. Spontaneous emission occurs without the influence of other photons and results in random phases and directions of emitted light. Incoherent light emission refers to light that does not have a fixed phase relationship between the photons, such as ordinary light bulbs. Thermal emission refers to light emitted from heated objects, like incandescent