What is the principle behind lasers?

Lasers operate based on the principle of stimulated emission of radiation, which leads to the emission of coherent light. In a laser, atoms or molecules are excited to higher energy levels through an external energy source. When these excited atoms return to their lower energy states, they release photons. The key aspect here is that these emitted photons have the same phase, frequency, and direction as the stimulating photon, resulting in a highly focused and coherent beam of light. This coherence is what distinguishes laser light from ordinary light sources.

In contrast, the other options do not accurately describe the functioning of a laser. Spontaneous generation of atoms, the use of prisms to focus light, and light reflecting multiple times are concepts related to different optical phenomena but do not capture the unique mechanisms that enable lasers to produce coherent light.