Model for the calculation of radiation trapping and description of the pinhole method

Radiation trapping is a well-known process that results in the lengthening of observed fluorescence lifetimes in laser materials with significant overlap in their emission and absorption spectra. The pinhole method is a measurement technique that allows the intrinsic fluorescence lifetime of an excited state to be determined in a nondestructive manner. A theoretical description of this method is proposed. A model is developed that identifies the lifetime extrapolated to a zero radius pinhole as the intrinsic fluorescence lifetime. The application of this method to bulk materials and thin discs is discussed.