THERMAL LENS SPECTROPHOTOMETRY IN AGAROSE GELS

In this study, the application of thermal lens spectroscopy to detecti on of analytes in agarose gels was examined. It was found that a long- term refractive index gradient is produced in the sample, in addition to the thermally induced refractive index gradient, and gives rise to a longterm thermal lens signal. It is argued that the most likely sour ce of the long-term signal is a concentration gradient formed in the s ample. The long-term refractive index gradient results in a focusing l ens, and is thus opposite to the thermal gradient. The formation of th is gradient requires as much as 500 s to reach equilibrium during cons tant irradiation. The existence of the long-term refractive index grad ient is verified by time-resolved Z-scan experiments. The signal resul ting from this gradient is termed the long-term thermal lens and is sh own to depend on temperature, is observed only for gelled agarose solu tions, and is sensitive to anisotropies in the sample.