The Influence of Light-Induced Periodic Structures on the Electronic Third-Order Optical Nonlinearity of As2S3 Films at 1550 nm Wavelength

The influence of laser-induced periodic structures on the third-order nonlinear optical response of chalcogenide glasses is of significant interest for advanced photonic applications. This paper presents a comparative study of the ultrafast third-order nonlinearity of unstructured and periodically micro-structured arsenic trisulfide (As2S3) thin films. The nonlinear optical response was investigated by the third-harmonic generation (THG) process using high-repetition-rate ultrashort laser pulses at the telecommunications wavelength λ = 1550 nm. Although high-repetition-rate laser pulses, typically generated by fibre lasers, can introduce cumulative thermo-optic effects due to sample heating, these effects are not responsible for the third-harmonic generation process, which is solely due to the ultrafast electronic third-order optical nonlinearity. The third-order nonlinear optical susceptibilities (χ(3)) of unstructured and periodically micro-structured As2S3 chalcogenide thin films are determined by THG experiments for the first time, to the best of our knowledge. For periodically micro-structured films, the parameter χ(3) was computed for two polarisation directions of the fundamental harmonic (FH) wave, parallel and orthogonal with respect to the direction of the periodic microstructure. The obtained results demonstrate that light-induced periodic micro-structuring enhances the third-order nonlinear optical response of As2S3 films. This enhancement is important for ultrafast photonic functionalities based on micro-structured As2S3 films.