Infrared technique for decoding of invisible laser markings

Heinz Haferkamp; Peter Jaeschke; Johannes Stein; Martin Goede

doi:10.1117/12.459560

15 March 2002 Infrared technique for decoding of invisible laser markings

Heinz Haferkamp, Peter Jaeschke, Johannes Stein, Martin Goede

Proceedings Volume 4710, Thermosense XXIV; (2002) https://doi.org/10.1117/12.459560
Event: AeroSense 2002, 2002, Orlando, FL, United States

Abstract

Counterfeiting and product piracy continues to be an important issue not only for the Western industry, but also for the society in general. Due to the drastic increase in product imitation and the request for plagiarism protection as well as for reducing thefts there is a high interest in new protection methods providing new security features. The method presented here consists of security markings which are included below paint layers. These markings are invisible for the human eye due to the non-transparency of the upper layers in the visible spectral range. However, the markings can be detected by an infrared technique taking advantage on the partial transparency of the upper paint layers in the IR-region. Metal sheets are marked using laser radiation. The beam of a Nd:YAG-laser provides a modification of the surface structure, resulting in dark markings due to the annealing effect. After coating of the laser-marked material, the markings are invisible for the bare eye. In order to read out the invisible information below the coating, an infrared reflection technique is used. The samples are illuminated with halogen lamps or infrared radiators. Many coating materials (i. e. paints) show a certain transparency in the mid-infrared region, especially between 3 - 5 micrometers . The reflected radiation is detected using an IR-camera with a sensitivity range from 3.4 - 5 micrometers . Due to the different reflection properties between the markings and their surrounding, the information can be detected.

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Heinz Haferkamp, Peter Jaeschke, Johannes Stein, and Martin Goede "Infrared technique for decoding of invisible laser markings", Proc. SPIE 4710, Thermosense XXIV, (15 March 2002); https://doi.org/10.1117/12.459560

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KEYWORDS

Metals

Laser marking

Thin film coatings

Infrared radiation

Optical properties

Reflection

Transparency

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