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A device that encourages atoms or molecules to emit light from certain waves and magnify that light, often producing very little radiation.

The laser is based on quantum phenomena in the transmission of energy by radiation. The exchange of radiation energy with atoms or molecules of the active medium in the laser (gas, crystal, plasma), instead of absorption and spontaneous emission of radiation, takes place by stimulated emission. This occurs when an atom or molecule in an excited state, i.e. in a state in which electrons are at a higher energy level, acts as an additional source of energy (e.g., white light or an electromagnetic field). The time number of atoms in the excited state (N2) becomes greater than the number of atoms in the unexcited state (N1) which is called population inversion. For the transition to the excited state, it is physically irrelevant in which way and way the energy is brought, while in the transition from the excited to the unexcited state, a quantum jump occurs, i.e., the emission of photons by which the energy corresponds to the difference of energy levels.

Laser-derived photons have one direction, frequency, polarization, and energy. The important properties of laser light is monochromatic, bright, collimated, polarized and coherent.