Determination of the quantum efficiency of the fluorescence of the solutions of organic dyes by diffraction on a thermal phase grating induced by laser radiation

A new absolute method was developed for the determination of the quantum efficiency of the fluorescence of organic dye solutions. The method is based on determination of the fraction of the excitation energy converted into heat from the efficiency of diffraction of probe radiation on a thermal grating of the refractive index induced by laser pulses in a dye solution. The efficiency of diffraction was practically unaffected by the processes of absorption and reemission of the fluorescence, so that in principle it should be possible to determine the fluorescence quantum efficiency more accurately than by traditional calorimetric methods. The new method is best suited to strongly fluorescing substances. A report is given of measurements of the fluorescence quantum efficiency of solutions of several dyes used widely in lasers and the results are in good agreement with the published data. The error in such measurements is 1.5% for substances with high quantum efficiencies.