Enhancement of the thermal lens signal induced by sample matrix absorption of the probe laser beam

The effect of the absorption of the probe laser beam by the sample matrix on the thermal lens signal of a solute was investigated for aqueous solutions of Tb(III), Yb(III), and Nd(III). The measurements were performed with a thermal lens instrument in which the pump and the probe beam were derived from a tunable Ti:sapphire laser. Thermal lens signals were found to be enhanced in the region where the probe beam overlapped with the absorption band of the sample matrix. The observed enhancement was confirmed further with samples of the same solutes (lanthanide ions) but in D2O, which does not absorb in the same spectral region as water. The enhancement may be due to the fact that absorption by the sample matrix led to a change in its refractive index and the production of a temperature gradient. In addition to fundamental importance, the observed enhancement can be used to improve the sensitivity of the thermal lens measurements by judiciously selecting a solvent that absorbs the probe laser beam. (C) 2002 Optical Society of America.