Electron excitation scheme.

Supplying a certain amount of energy (called excitation energy) to an electron so that it enters a higher energy state. The energy is delivered by an electromagnetic wave (photon), or by collision with another particle. An electron at a higher energy level is called excited. It can get rid of its energy by emitting a photon and jump to a lower energy state, this process is called deexcitation. The state with the lowest possible amount of energy is called the ground state. Excitation and deexcitation of electrons is used, for example, in lasers to produce a coherent monochromatic beam of photons.