Abstract

Single-frequency laser heterodyne measurements in a modified Jamin interferometer have been used to study the nonradiative energy loss of isolated rhodamine 6G molecules in solution. Pure methanol and several methanol-based solvents containing the quencher potassium iodide were studied. Simultaneous measurement of both the fluorescent intensity and the photothermal phase modulation induced by AM argon-ion laser excitation allows absolute determination of both the quantum efficiency η and the fraction of absorbed photoenergy converted to heat. Broadband fluorescent intensity was measured with a photodiode. Photothermal phase modulation was synchronously detected by operating the Jamin interferometer in quadrature and passing the resultant linear intensity modulation to a lock-in amplifier. Rhodamine 6G concentration as low as 5 × 10⁻⁹ g/m liter could be used. Typical Kl quencher concentrations were in the 0.33-4.5-mg/m liter range. The absolute quantum efficiency of rhodamine 6G at zero quencher concentration was found to be 96 %. The fraction of absorbed energy converted to heat at zero quencher concentration was 12%.

© 1985 Optical Society of America