Micromechanical scanning mirrors with highly reflective NIR coatings for high power applications
This paper addresses different highly reflective optical coatings on micro scanning mirrors (MSM) for applications in the NIR-spectral region to enable new applications like laser marking and material treatment at high optical power density. In the case of MSM with an unprotected Al coating, the absorption limits the maximal power density because of induced heating. The damage threshold for unprotected Al coatings was investigated. In addition highly reflective enhanced metallic and dielectric multilayer coatings for the NIR have been developed and characterized. These coatings resolve the problems of unprotected aluminum coatings related to NIR absorption and the resulting limitation of applicable laser power density. The coatings ensure a high reflectance even in corrosive environments. Enhanced metallic broadband reflectors reach a reflevctivity of 98.7% at 1064nm whereas narrow-band dielectric multilayer coatings reach a reflectivity of 99.7% at 1064 nm.