So far, laser calorimetry (LCA) as absorptance measurement procedure according to ISO 11551 has been commonly performed at a variety of selected laser wavelengths. Thus, this procedure has been a valuable tool for optimization processes of dielectric coatings. For an even more comprehensive detection of any absorbing contribution in a dielectric layer stack a free selectable test wavelength gives more detailed insights in optics characterization. According to this approach an OPO system was implemented in a laser calorimetric test bench. By this, a tunable laser source with sufficient laser power is available to conduct calorimetric absorptance measurements. Results of detailed investigations of the contribution of the material constituents of a dielectric optical component are presented in this paper.