an article for use in an oct method , the article comprising a solid substrate and nanoparticles dispersed in or on the substrate in at least one light transmissive portion of the article such that the nanoparticles result in an increased extinction of the light transmissive portion along a transmission direction of the light transmissive portion compared to the substrate being free of nanoparticles . the extinction of the light transmissive portion along the transmission direction is less than 6 , wherein the extinction is defined as a negative decadic logarithm of a ratio of an intensity of light which is transmitted through the light transmissive portion to an intensity of light which is incident on the light transmissive portion , wherein the light is in at least one of a visible and a near infrared wavelength range .