excitáció

Excitation, or excitáció in Hungarian, refers to the process whereby a system is promoted from a lower-energy (ground) state to a higher-energy state. In physics and chemistry, excitation commonly describes the absorption of energy by atoms, molecules, or nuclei, causing an electron or nucleon to occupy a higher quantum level. The excited state is typically unstable, leading to emission of energy as the system relaxes back to its ground state. This relaxation can occur via spontaneous emission (e.g., fluorescence, phosphorescence, and scintillation), stimulated emission (the basis of laser operation), or nonradiative pathways such as internal conversion and vibrational relaxation.

In atomic and molecular physics, the absorption of photons induces electronic excitation, often characterized by discrete energy levels and spectral lines. In nuclear physics, gamma radiation can excite nucleons, producing isomeric states that later decay by gamma emission. Solid-state physics frequently deals with excitons, bound electron–hole pairs created in semiconductors upon photon absorption, which play a critical role in optoelectronic devices.

In biology, excitation underpins neuronal signaling: the depolarization of a neuron's membrane potential triggers the firing of action potentials. In muscle physiology, calcium ions release from the sarcoplasmic reticulum cause excitation–contraction coupling, allowing muscle fibers to contract.

Experimentally, excitation is examined using techniques such as spectroscopy, time-resolved fluorescence, and pump–probe laser methods. Theoretical models employ quantum mechanics, the density functional theory for electronic excitation, and master equations for open-system dynamics. Excitation phenomena are foundational to technologies ranging from lasers and LEDs to biomedical imaging and quantum information processing.