Spontaneous Emission - Rate of Spontaneous Emission

Rate of Spontaneous Emission

The rate of spontaneous emission (i.e., the radiative rate) can be described by Fermi's golden rule. The rate of emission depends on two factors: an 'atomic part', which describes the internal structure of the light source and a 'field part', which describes the density of electromagnetic modes of the environment. The atomic part describes the strength of a transition between two states in terms of transition moments. In a homogeneous medium, such as free space, the rate of spontaneous emission in the dipole approximation is given by:

where is the emission frequency, is the index of refraction, is the transition dipole moment, is the vacuum permittivity, is the reduced Planck constant and is the vacuum speed of light. (This approximation breaks down in the case of inner shell electrons in high-Z atoms.) Clearly, the rate of spontaneous emission in free space increases with . In contrast with atoms, which have a discrete emission spectrum, quantum dots can be tuned continuously by changing their size. This property has been used to check the -frequency dependence of the spontaneous emission rate as described by Fermi's golden rule.

Read more about this topic:  Spontaneous Emission

Famous quotes containing the words rate, spontaneous and/or emission:

    You are more than entitled not to know what the word ‘performative’ means. It is a new word and an ugly word, and perhaps it does not mean anything very much. But at any rate there is one thing in its favor, it is not a profound word.
    —J.L. (John Langshaw)

    What is saved in the cinema when it achieves art is a spontaneous continuity with all mankind. It is not an art of the princes or the bourgeoisie. It is popular and vagrant. In the sky of the cinema people learn what they might have been and discover what belongs to them apart from their single lives.
    John Berger (b. 1926)

    Approximately 80% of our air pollution stems from hydrocarbons released by vegetation, so let’s not go overboard in setting and enforcing tough emission standards from man-made sources.
    Ronald Reagan (b. 1911)