Radiative damping constant

An excited atom can emit its excitation energy as spontaneous radiation (Sect. 2.7). In order to investigate the spectral distribution of this spontaneous emission on a transition Ei Ek, v/t shall describe the excited atomic electron by the classical model of a damped harmonic oscillator with frequency co, mass m, and restoring force constant k. The radiative energy loss results in a damping of the oscillation described by the damping constant y. We shall see, however, that for real atoms the damping is extremely small, which means that y 0). ... 

The preceding discussion has shown that both elastic and inelastic collisions cause spectral line broadening. The elastic collisions may additionally cause a line shift which depends on the potential curves E. (R) and E (R). This can be quantitatively seen from a model introduced by LINDHOLM [3.6], which treats the excited atom A as a damped oscillator which suffers collisions with particles B (atoms or molecules). In this model inelastic collisions damp the amplitude of the oscillation. This is described by introducing a damping constant such that the sum of radiative and col-lisional damping is represented by y = y + y qi From the derivation in Sect.3.1 one obtains for the line broadened by inelastic collisions a Lorentzian profile with halfwidth (3.38)... 

For the present we assume that the damping constant is determined only by the radiative lifetime of the excited atom, r=l/x. From equation (15,1) we see that at zero magnetic field the fluorescent light is linearly polarized in a direc-... 

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