A new field in laser processing is opened by a laser-induced modification of the optical properties, i.e. the refractive index, absorption- and scattering-coefficient, inside transparent materials, preferentially optical glasses. Ultra short laser pulses are capable of inducing these modifications without cracking or even melting the glass matrix. The femtosecond and in some cases even picosecond laser technology allows to control and modify the optical properties in the bulk on a sub-µm scale. 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 on a microscopic scale. The technical potential for optical applications is challenging and on the verge to be exploited. New results on nik-engineering using ultra-short laser pulses at a wavelength of 800 nm was investigated for special glasses with semi-conductive nano-particles, i.e. photo-chromic and GG/RG filter glasses. This paper discusses the laser-induced optical modification inside these glasses for different laser fluence and shot numbers,
addressing also the possible technological relevance of these effects in respect to decorative work, micro-tagging, and other functional structures.