Intense laser fields have the potential to take the interaction with dielectric media to the non-linear regime. Because of this, dielectric multilayer films were the necessary technology step to take the newly developed laser to the power and energy levels where it could serve the multiple applications we know today. Over these past decades, a most diverse matrix of laser parameters was developed. Systems with highest output powers and a large variety of emission wavelengths, as well as pulse durations spread over 15 orders of magnitude, have entered industrial and scientific applications and have contributed significantly to technological progress of society. Design, development and application of these systems require a detailed understanding of the light - matter interaction and a precise quality control in the development and production process of the optical components and specifically in the thin films. Characteristics such as transmission/reflection and phase properties, losses like absorption, fluorescence and scattering, durability towards hostile environments and high intensity laser fields and numerous further characteristics need to be understood and measured at the laser parameter set of the application. This course will provide an overview on the techniques developed and a guide on how to interpret the various resulting data.