Prototyping platform for laser-based sensor technologies: Inspection of conversion coatings on alumina

Transferring laser-based sensors into industrial applications, for instance for the contact-& destruction-free inline quality control of alumina alloys, is very challenging due to laser-safety requirements and the complex implementation in individual technological infrastructures. In order to open laser-based sensor technology even for small to medium size enterprises, we introduce a prototyping platform for laser-based sensor technologies that enables the fast, error-free, flexible and low cost transformation into industry. As an example, the transformation of the laser-based sensor concept using coherent light scattering at technical insulating films is shown. The transformation of this type of sensor for inline quality control is particularly demanding due to the requirement of probing transparent conversion coatings, with a thickness of less than 70 nm so that commonly applied electronic techniques fail. The conversion films are produced on the top of cold-rolled, unpolished alumina so that coherently scattered laser light is regarded as superposition from diffuse scattering processes at the surfaces/interfaces, inclusions and/or layer imperfections. Analysis is realized by extending the principle approach of reflectometry by considering the role of diffuse and specular scattering together with the concepts of light interferometry. The functionality of the transformed sensor is successfully validated using five different conversion coating thicknesses on AA3003 alumina substrates.