Radiation trapping in a laser dye medium, rhodamine 6G in alcohol

Prolonging of decay time τ due self-absorption of fluorescence is estimated from the spectra for a cylinder of infinite length. The basis of the calculation is the "a" factor-the probability of self-absorption of an emitted photon, which is solved by a Monte-Carlo integration. For the experimental conditions used in a typical flashlamp-pumped dye oscillator, the molecular decay time of 3.5 ns is extended to 4.8 ns, and does not change as the oscillator is scaled in dimension. It is the prolonged τ that determines pump and signal saturation fluxes, lowering the fluxes, and such radiation trapping contributes significantly to making rhodamine 6G an effective laser dye.