Photothermal sensing techniques for thin-film characterization

Photothermal sensing techniques are widely used in materials characterization and are particularly useful for noninvasive inspection of thin film coatings. The specific applications include measuring optical absorption, characterizing thermal conductivity, detecting local defects, as well as monitoring laser-interaction dynamics and determining laser modification thresholds as well as thermal/acoustic impedance at boundaries of multilayers. This paper introduces the basic concepts and principles of photothermal sensing techniques, the various detection methods, and the progress made during the last a few years in applying these techniques to characterization of thin film coatings, particularly those for high power laser applications. The further potential and limitations of these techniques will also be discussed, with emphasis on spectroscopic studies and in-situ investigations.