MEASUREMENT OF THE ABSOLUTE FLUORESCENCE QUANTUM YIELD OF RHODAMINE-BSOLUTION USING A DUAL-BEAM THERMAL LENS TECHNIQUE

The dual-beam thermal lens technique has been found to be very effecti ve for the measurement of fluorescence quantum yields of dye solutions . The concentration-dependence of the quantum yield of rhodamine B in methanol is studied here using this technique. The observed results ar e in line with the conclusion that the reduction in the quantum yield in the quenching region is essentially due to the non-radiative relaxa tion of the absorbed energy. The thermal lens has been found to become abberated above 40 mW of pump laser power. This low value for the upp er limit of pump power is due to the fact that the medium is a resonan tly absorbing one.