Optical properties of Ge-Sb-Se thin films induced by femtosecond laser

The germanium antimony selenide (Ge-Sb-Se) film has emerged as an appealing infrared material with good photosensitivity, large nonlinear coefficient and high transmittance in infrared region. In particular, an infrared optical motherboard can be fabricated in the film by femtosecond (fs) laser micromachining. A detailed quantitative structural and optical characterization for 36 different regions in the film induced by fs laser is reported. By adjusting the laser power and scanning speed, different induced regions in chalcogenide films were obtained by laser direct writing. The size of the focused spot was about 0.3μm which was consistent with the distance between two adjacent lines fabricated into the Ge-Sb-Se film with the thickness of 1.4μm. The refractive index of the film was obtained by using the improved Swanepoel method with an accuracy of better than 0.1%. The transmittance, refractive index, absorption coefficient and optical band gap as a function of the power density were obtained. The results showed that the transmittance, refractive index and optical band gap of the film decreased, while the absorption coefficient increased with the increase of laser power and the decrease of translation velocity gradually. Raman spectroscopy indicated that the Ge–Ge bonds in the Ge2Se6∕2 ethane structure and the Se–Se homopolar bonds in Seμ long chain or in the Se8 ring were reduced after laser irradiation, and more edge-sharing GeSe 4 tetrahedral structures were formed which resulted in the refractive index change of the film. This work should provide a useful guideline for the preparation of versatile photonic devices based on Ge-Sb-Se films. •The interaction between focused 800 nm femtosecond laser and Ge-Sb-Se film was investigated quantitatively.•The optical band gap decreases and the absorption coefficient increases after laser irradiation.•The film after laser irradiation exhibits 2% photo-expansion and the refractive index of the film decreases 0.01–0.08.•The refractive index change and photo-expansion remain a linear relationship.