作者: D. E. McCumber
关键词: Spontaneous emission 、 Absorption spectroscopy 、 Absorption (logic) 、 Stimulated emission 、 Atomic physics 、 Energy (signal processing) 、 Spectral line 、 Solid angle 、 Omega 、 Physics
摘要: Relations described by Einstein connecting the rates of spontaneous emission, stimulated and absorption radiation an atomic system in free space are generalized to apply broadband spectra quantized systems dilutely distributed a dielectric medium. Although gross features emission can be qualitatively different (especially at low temperatures), various connected any specific frequency simple expressions. For two-level imbedded medium temperature $T$, typical equations stimulated-emission cross sections $\ensuremath{\sigma}(\ensuremath{\omega})$ rate $f(\ensuremath{\omega})$ photons per unit solid angle interval are: ${\ensuremath{\sigma}}_{e}(\ensuremath{\omega})={\ensuremath{\sigma}}_{a}(\ensuremath{\omega})\mathrm{exp}[\frac{\ensuremath{\hbar}(\ensuremath{\mu}\ensuremath{-}\ensuremath{\omega})}{\mathrm{kT}}]=f(\ensuremath{\omega}){(\frac{2\ensuremath{\pi}c}{\ensuremath{\omega}n})}^{2}$, where $\ensuremath{\hbar}\ensuremath{\mu}$ is temperature-dependent excitation potential $n$ index refraction host material.