| The Femtosecond(fs)laser micro-nano processing has the advantages of small thermal effect,high precision,true three-dimensional machining capability,lower two-photon absorption and higher third-order nonlinearity,so it is important in the field of micro-nano photonic devices.Chalcogenide films have a wide infrared transmission spectrum and special photosensitivity,which are important carriers for miniaturization and integration of infrared optical devices.Fs laser-induced transparent chalcogenide film modification is widely used in the field of preparation of infrared micro-nano structures and devices such as optical microfluidic lab-on-chip,infrared microcavity lasers,three-dimensional photonic crystal,etc.However,due to the difficulty in measuring and characterizing the film parameters after induction,especially the refractive index,the relationship between the chalcogenide film modification and laser parameter control,and the film modification mechanism have not been grasped.This makes it difficult to manufacture high-precision micro-nano optical devices using fs lasers machining based on the Chalcogenide films.Aiming at the above problems,this paper systematically designed the experimental scheme,proposed measurement and characterization methods of the film parameters,developed a series of technologies,including transmission spectra testing and filtering,transmittance calibration,and high precision calculation of the refractive index,of chalcogenide films.Theoretically,a segmented filtering method was proposed to obtain smooth and accurate thin film transmission spectra,a translation matching method was developed to calibrate the transmittance of the film,the calculation accuracy of the film refractive index after segmented filtering and transmittance calibration is analyzed.The results show that the calculated accuracy of the refractive index of the thin film after optimizing the transmission spectrum curve is better than 0.5%.Experimentally,the modification of Ge20 and Ge28 thin films induced by fs laser was studied in this paper.The relationship between various optical parameter changes was obtained,and the mechanism of thin film modification was analyzed by micro Raman spectroscopy.The results show that the Ge20 film exhibits photo-expansion and refractive index decrease after induction,and there is a linear relationship between them.The glass network connectivity of the Ge20 film decreases after induction;Ge28 film has a periodic refractive index distribution after laser induction.The periodic refractive index difference increases with the increase of the laser power density,and the internal defects of the film decrease after induction,the film tends to a stable state from metastable state. |
