Spontaneous emission rate modification

Amos, R. M. and Baines, W. L. (1997). Modification of the spontaneous emission rate of Eu3+ ions close to a thin metal mirror Physical Review B 55 7249-7254. 

The Purcell s original idea [10] on modification of photon spontaneous emission rate is extended to modification of photon spontaneous scattering rate. Simultaneous account for local incident field and local density of photon states enhancements in close proximity to a silver nanoparticle is found to provide up to lO -fold Raman scattering cross-section rise up. Thus, single molecule Raman detection is found to be explained by consistent quantum electrodynamic description without chemical mechanisms involved. 

Bjork, G. (1991). Modification of spontaneous emission rate in planar dielectric microcavity structures. Physical Review A, Vol. 44, No. 1, pp. 669—681. 

However, the degree of modification we can exert on the properties of optical phenomena by introducing a complex medium appears to be limited. These limits, called conservation or sum rules, seem to have fundamental physical reasons. For instance, the Eamett-Loudon sum rule [1] places a restriction on the modification of spontaneous emission rate regardless of the means used and is derived from the general causality-related laws such as the Kramers-Kronig relation. 

Hence the only relevant modification of the spontaneous emission rate due to the presence of fhe parabolic mirror is fhe replacement of the plane traveling waves/(n,r) = by the standing waves... 

Both quantum and optical DOS, subject to modification owing to inhomogeneities, nevertheless obeys fundamental conservation relations. It appears possible only to redistribute the states spectrally and/or spatially, but not to alter the underlying physics of a vacuum by changing their total number. This in turn gives rise to constraints on DOS-affected phenomena, such as conservation of integrated modified spontaneous emission rate [3],... 

During last decades, the concept of the photon DOS is extensively discussed with respect to elementary photon emission and scattering events. Formulation of the photon DOS concept was promoted by pioneering papers by Purcell in 1947 [19], and Bykov in 1972 [20]. They predicted the considerable modification of spontaneous emission rate in cavities and in periodic medium, respectively. Today, the modification of spontaneous emission and scattering of light constitutes a body of modern nanophotonics (see e.g. [21] and refs, therein). Local photonic DOS which in many instances is an optical counterpart of local electronic DOS in doped semiconductors still lacks a solid definition [22]. 

The effect of quantum interference on spontaneous emission in atomic and molecular systems is the generation of superposition states that can be manipulated, to reduce the interaction with the environment, by adjusting the polarizations of the transition dipole moments, or the amplitudes and phases of the external driving fields. With a suitable choice of parameters, the superposition states can decay with controlled and significantly reduced rates. This modification can lead to subnatural linewidths in the fluorescence and absorption spectra [5,10]. Furthermore, as will be shown in this review, the superposition states can even be decoupled from the environment and the population can be trapped in these states without decaying to the lower levels. These states, known as dark or trapped states, were predicted in many configurations of multilevel systems [11], as well as in multiatom systems [12],... 

To demonstrate experimentally the modification of the spontaneous decay rate, it is not always necessary to go to single-atom densities. The experiments where the spontaneous emission is inhibited can also be performed with higher densities. However, in the opposite case where an increase of the spontaneous rate is observed, a large number of excited atoms increases the field strength in the cavity and the induced transitions disturb the experiment. 

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