APPLICATION OF LASER-INDUCED THERMAL LENS OSCILLATION TO CONCENTRATION MEASUREMENT IN ORGANIC SOLUTIONS

Laser-induced thermal lensing effect was studied to analyze solute concentration in organic solutions. A new method for concentration measurement was proposed based on the thermal lens oscillation, and demonstrated for uranyl nitrate in 30%tri-n-butyl phosphate solution. A pulsed dye laser system was used to excite uranyl ions so as to create a local temperature gradient in the sample solutions. This thermal effect led to a change of refractive index which could be detected by the divergence of the probe beam, for which a He-Ne laser was used. When the laser beams propagated horizontally below the free surface of the liquid and the depth of the beam position was increased, the signal electronically obtained by the probe beam departed from steadiness and exhibited periodic behavior (thermal oscillation). The boundary of the thermal lens oscillation was clearly determined by fast Fourier transform spectral analysis of the obtained signal, and related with absorbance of the sample solution. The concentration difference of 1 x 10(-4)M uranyl ion was detected by applying this procedure. This method is expected to be useful for verifying concentration of nuclear materials below the concentration limit.