Thermal lens microscopy is a very sensitive photothermal technique with many applications in environment, organic chemistry, biochemistry and biomedicine. This paper shows the development of a thermal lens microscope for asphaltene analysis. Two coaxial laser beams were pumped through the microscope objective to the sample. The wavelength of the excitation beam was selected to coincide with an absorption band of the analyte, and the wavelength of the probe beam was chosen so that the sample solution has no absorption. When the analyte molecules absorb the excitation beam, they emitted heat increasing the temperature in the confocal region that decreases the refractive index generating a lens-like object. This instrument was used to measure the response of thermal lens in different Venezuelan asphaltene solutions, finding variations in the signal with the concentration of asphaltene and the degree of aggregation or flocculation of the sample in the solvent.

© 2015 Optical Society of America

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