A laser beam is emitted from what?

The correct choice, active medium, refers to the material in which the laser action occurs. In a laser, the active medium is responsible for the stimulation of the atoms or molecules to emit coherent light. This medium can be solid, liquid, or gas, depending on the type of laser. For instance, in solid-state lasers, a solid crystal or glass serves as the active medium; in gas lasers, the gas itself acts as the active medium.

The active medium is crucial because it is excited by an external energy source, such as electrical discharge or a flash lamp, which causes the atoms to enter an excited state. When these atoms return to their ground state, they release energy in the form of photons, which creates the laser beam. This coherent light, characterized by its monochromatic property, is what distinguishes laser emissions from other light sources.

Other options do not correctly describe the role of emitting a laser beam. Solid medium, for example, could refer to the physical state of the active medium but does not encompass all types of laser media. Passive medium is not relevant in this context as it generally refers to materials that do not contribute to the emission process. Lastly, superficial medium is not a recognized term in laser technology, further establishing the active