Spectrophotometric bench dedicated to the characterization of micro-patterned optical coatings

Characterization of the spectral transmission of micro-patterned optical coatings requires accurate and highly localized measurement means. However, the capabilities of commercial equipments are generally limited, and either they do not provide sufficient spatial and spectral resolution, or they modify the spectral transmittance properties of the sample by using a large half angle illuminating light cone. In this work, we propose a new approach based on the recording, using a high performance photodiode array camera, of monochromatic magnified images of the sample illuminated by a filtered and fiber-coupled super-continuum laser source. In such case, the spatial resolution is directly given by the size of the individual CCD pixels and by the magnification of the imaging objective, while the spectral resolution is defined by the slit width of the filtering monochromator. This paper will give a detailed description of the main features of this spectrophotometric bench, and will demonstrate its ability to record the spectral transmittance of patterned samples with micrometer spatial resolution and sub-nanometer spectral resolution in the visible and near infrared ranges.