Combined laser calorimetry and surface thermal lens technique for optical coating characterization

A combined laser calorimetry (LC) and surface thermal lens (STL) technique with a continuous-wave (cw) modulated excitation is developed for characterizing the absorption properties of optical coatings. LC and STL signals are simultaneously obtained with highly reflective coating samples irradiated at 1064 nm. With a modulated irradiation power of 2.6 W, the limits of absorptance detection for the LC and STL signals are approximately 1.2×10^-6 and 0.5×10^-6, respectively. The influences of different excitation parameters (modulation frequency, excitation-beam power and irradiation time) on the absorptance measurements are experimentally analyzed. The applicability of the combined LC and STL technique to the investigation of the laser-induced absorption changes of optical coatings in an absolute absorptance scale is demonstrated. PACS 42.87.-d; 78.20.-e