Sub-surface 3d structures by laser-induced modification of the optical properties of transparent materials

A new field in laser processing is opened by this method of modifying the optical properties, i.e. the refractive, index, absorption- and scattering-coefficient, inside the material. Focusing ultra. short laser pulses inside the transparent media allows to control and modify their optical properties. This is referred to as nik-engineering(TM), relating the experimental technique to changes of the complex refractive index (n + ik). Three dimensional patterns of the (n + ik) modifications can be achieved in the subsurface region even on a microscopic scale. New results in nik-engineering obtained in our application laboratory are presented using different optical materials. The results in laser nik-engineering. of photo-chromic glass using ultra short laser pulses at a wavelength of 800 nm are presented to the best of our knowledge for the first time. We discuss the results and the possibilities of nik-engineering and consider the technological relevance with respect to decorative work, micro-tagging, and other functional-structures.