Spontaneous emission

The spontaneous emission, known in older literature as quantum -like emission is a quantum mechanical phenomenon. It involves the emission of photons in the transition between states with different energy content of atoms or molecules. The spontaneous emission takes place, in contrast to the stimulated emission, without external action instead. So you heard about the decay processes and the random processes.

The basic idea was first published by Albert Einstein in 1916 and 1917.

Description

The spontaneous emission takes place without any external influence. The exact time at which an energetically excited system emits a photon, is not predictable. Instead, quantum physics only allows the specification of a probability that within a certain period of time instead finds an issue. You can for example be characterized on the half- time after which an ensemble of excited atoms or molecules just half of the particles per one photon emitted, or even about the so -called lifetime of the excited state.

In the context of quantum mechanics, which describes, among other things, the structure of atoms and molecules, allows the absorption of a photon and the stimulated emission understand that. Both are activated by irradiation of an electromagnetic wave and differ in their mathematical description only by a sign. The spontaneous emission is, however, not initially understand. Contrary to intuition is according to the rules of quantum mechanics in the absence of external disturbances, a state of higher energy stable.

The mechanism of the spontaneous emission was therefore understood only in the framework of quantum electrodynamics, which can also describe the creation and annihilation of photons. Thereafter, the vacuum of vacuum fluctuations some of the electromagnetic field is satisfied. These vibrations correspond to the energetic ground state and can therefore in principle not be destroyed by absorption. The phenomenon of spontaneous emission can now be qualitatively and quantitatively ultimately attributed to stimulated emission, which is triggered by these vacuum fluctuations.

Mathematical Description

The number of spontaneous emissions per volume and time is proportional to the particle number density in the excited state.

N is the number of excited particles, n is the particle number density, V is the volume. However, in a sufficient amount, the total intensity is independent of the number of particles of particles because emitted photons are not absorbed by excited particles. With a sufficient amount to keep emission and absorption of the scale, so that the intensity is (including stimulated emission ) is not exceeded by the Planck formula.