DECAY OF EXCITED ATOMS IN ABSORBING DIELECTRICS

We present calculations of the rates of decay of an excited atom embed ded in an absorbing dielectric. Decay can occur by spontaneous emissio n into transverse radiative modes of the electromagnetic field and by Joule heating via longitudinal coupling of the atom to the dielectric. The spontaneous emission (transverse) decay rate is modified in a die lectric, being the free-space rate multiplied by the real part of the refractive index at the transition frequency of the atom. There is a f urther modification due to the difference between the macroscopic diel ectric field and the local field at the position of the atom. In addit ion there is a longitudinal decay rate which is proportional to the im aginary part of the dielectric constant and therefore vanishes in non- absorbing media. We derive expressions for each of these rates of deca y and discuss the physical mechanisms leading to them.