Determination of thin-film thermal parameters by photoinduced thermal radiation measurements

Several physical phenomena manifest when dealing with lasers and optical thin films, including scattering, laser-induced damage threshold, and optical absorption, which induces temperature elevation and thermal emission in thin films. This contribution focuses on addressing this thermal phenomenon. The first step requires an accurate theoretical prediction of photo-induced thermal radiation, a task undertaken by the CONCEPT team at Institute Fresnel. Subsequently, an experimental facility was built to conduct measurements of photo-induced thermal emission in temporal regime (ns). Measurements were conducted using different types of samples, including absorbers, single layers, and bilayers. The current state of the instrument has demonstrated robustness in terms of correlation with simulated data. This robustness enabled the treatment of the inverse problem to determine sample thermal parameters. Thermal emission depends not only on incident source parameters (such as energy and pulse duration) but also on sample parameters like complex index, thickness and design, thermal conductivity and diffusivity. This contribution explores the influence of thermal parameters on thermal radiation, particularly for metallic single layers. Bulk values of conductivity are compared with those that are determined from thermal radiation measurements.