The use of a confocal detection scheme in a dual-beam thermal-lens microscope is presented. It allows the measurement of absorption factors smaller than 10(-6) using a heating laser power of 100 mW incident on the sample. A simple mathematical model based on gaussian beam propagation is presented that takes into account the main features of the instrument: the confocal detection scheme and the presence of chromatic aberrations in the objective lenses, and that allows to estimate the sensitivity and resolution of the instrument. This model is validated by experimental measurements on different test samples. Results are presented that prove a 450 nm axial resolution when using a NA = 1.2 water immersion objective lens.