An examination of the fluorescent process in simple and detailed models of multilevel atoms, expressed in terms of the parameter $P_{\mathrm{ij}}$/$C_{\mathrm{ij}}$ where $P_{\mathrm{ij}}$ and $C_{\mathrm{ij}}$ are, respectively, the photoexcitation rate and the collisional excitation rate in the pumped resonance transition i-j, shows that three distinct regimes exist over the full range of this parameter which may be usefully exploited. The regimes are defined by I, $P_{\mathrm{ij}}$/$C_{\mathrm{ij}}$≲1; II, $P_{\mathrm{ij}}$/$C_{\mathrm{ij}}$≫1, $P_{\mathrm{ij}}$≪$C_{\mathrm{ki}}$; III, $P_{\mathrm{ij}}$/$C_{\mathrm{ij}}$≫1, $P_{\mathrm{ij}}$≫$C_{\mathrm{ki}}$, where $C_{\mathrm{ki}}$ is the collisional rate populating the source level i. Regime I is characterized by sensitivity of fluorescent-fluorescent line intensity ratios to the photoexcitation rate $P_{\mathrm{ij}}$. Regime II is characterized, on the other hand, by insensitivity of these line ratios to $P_{\mathrm{ij}}$. If regime III is reached, even fluorescent-nonfluorescent line ratios become independent of $P_{\mathrm{ij}}$. A concrete application of the analysis has been made to the resonant photoexcitation of a carbonlike ion.

• Received 2 March 1987

DOI:https://doi.org/10.1103/PhysRevA.37.1003