For calorimetric measurements by a photothermal technique such as the thermal lens method, it is important to ensure that only the thermal effect can be detected. A method for evaluating the contribution of the pure thermal lens (TL) in the observed "TL(ex) signal" is presented in a case in which the TL signal is contaminated by the transient absorption and/or the population lens effect. This method is based on a solvent dependence of the signal intensity together with the concave-convex lens (CCL) method. As an example, this method is applied to evaluate the quantum yield of the triplet formation of anthracene probed at a wavelength near the triplet-triplet absorption.