A method for converting aromatic hydrocarbons by contacting an aromatic hydrocarbon starting material including benzene and having a non-aromatic compound content of 1% by weight or less, with a catalystto generate useful C7 and C8 aromatic hydrocarbons while reducing the catalyst deactivation. Indications of information decoded therefrom may be superimposed andor provided by highlighting. Further, an optical detector is coupled to the beam path of the surgical laser to create a sequence of cross-sectional images.