Metal-dielectric absorbers with magnetron sputtering technique

In this paper, we show how thin film absorbing coatings can be designed with multilayers using both metallic and dielectric materials involving some thicknesses that are very low down to some nanometers. Such multilayers enable to reach a very low level of reflectance and a zero value of transmittance, which can be a solution for stray light reduction in optical systems. After a description of the design steps, we will present the manufacturing of such multilayer stacks using magnetron sputtering technique and we will see how such coating technique is very well suited for production due to its high process reproducibility even for very thin layers required in metal-dielectric absorbers. Monitoring of such coatings is also presented with the help of a powerful in situ optical system developed in collaboration with Institut Fresnel that allows characterization of in-situ refractive indices of deposited materials and broadband monitoring of the multilayer stack. Many results will be given on qualification samples, such as environmental tests and spectral characterizations that show the stability of the performances in severe environmental conditions. At last, we will focus on the spectral and angular scattering behavior of such absorbing coatings and we will present several measurements performed on glass or metallic substrates with different roughnesses.