Formation And Femtosecond Laser Damage Of Te-As-Se Glasses

As a novel infrared transmission material,chalcogenide glasses（Ch Gs）have many prominent features including ultra-wide infrared transmission range,low phonon energy,high linear and non-linear refractive index,excellent thermal stability and tunable composition,thus are widely used in various applications such as infrared optics,nonlinear optics and optoelectronics.Among many Ch Gs,Te-As-Se（TAS）Ch Gs have attracted great attention due to their excellent infrared optics and nonlinear optical properties,especially their ultra-wide transmission spectra（2-18μm）can detect most molecules within the fingerprint regions.Although TAS glasses have been studied early,various performance parameters are still scarce,such as the thermodynamic and optical parameters used in the preparation and realization of TAS infrared optical waveguide devices.Because of high nonlinear optical performance,the laser,especially the femtosecond（fs）lasers,are often used to process or pump the Ch Gs.However,the ultra-short pulses and extremely high peak powers of fs lasers exceed the damage thresholds of Ch Gs,resulting in device destruction.Therefore,it is necessary to investigate the damage mechanism of TAS Ch Gs under the irradiation of mid-infrared（MIR）fs laser,so as to provide scientific guidance for the preparation of TAS optical waveguide devices,the laser transmission and pumping applications of TAS fibers.In this dissertation,we firstly introduced Ch Gs and their related applications,especially the study progress of TAS glasses in detail.The current status of fs lasers applied to Ch Gs,the applications of fs lasers on the chalcogenide materials,and the damage of Ch Gs induced by fs lasers were summarized.Secondly,a series of TAS glasses was prepared using melt-quenching method.The characterization methods for performance parameters were introduced,and an experimental platform for the MIR fs laser irradiation on the Ch Gs was set up.In addition,the fs lasers mechanism of optical materials,the measurement and calculation methods of glasses damage threshold were introduced.Finally,the composition-property-structure of TAS glasses and the damage characteristics of MIR fs laser were systematically analyzed.The details are as follows:.（1）The glass-forming domain of TAS glasses was determined and divided into three regions according to the thermal stability.With the increase of Te content,TAS glasses exhibited the following characteristics:（1）both the glass transition temperature and thermal stability decreased gradually,resulting in the increase of crystallization tendency;（2）the Vickers hardness became smaller,while the mechanical properties became worse;（3）both the density and linear refractive index increased;（4）both the short-wave and infrared cut-off edges were red-shifted,and the optical band gap became narrower.Additionally,when the average coordination number（MCN）was 2.4,the glass network structure was the densest.Meanwhile,the density was the smallest and the molar volume was the largest.The Vickers hardness was positively correlated with the MCN.Raman spectroscopy showed that there were three main peaks at 168,193,and 227 cm^-1in TAS glasses,respectively,which were mainly attributed to the main vibration peaks of the[As Se₃],[Te As Se₂]and[Te₂As Se]pyramid structural units utilizing Gaussian simulation.（2）The stoichiometric ratio glass had the best resistance to fs laser damage.With the increase of Te content,the fs laser-induced damage threshold（LIDT）gradually decreased,indicating the anti-damage performance decreased.In addition,the LIDT of the purified glass improved.The effects of laser parameters（power,wavelength,number of pulses,and repetition frequency）on LIDT were studied.It was found that:（1）as the laser power increased,the area（diameter）and depth of the circular crater on the glass surface gradually increased;（2）as the laser wavelength became larger,the multiphoton ionization effect was strengthened due to the decrease in photon energy,and the LIDT became larger,improving damage resistance performance;（3）the LIDT became smaller with the increase of number of laser pulses;（4）when the laser repetition frequency was less than 100 Hz,the LIDT decreased slowly,and when it exceeded 100 Hz,LIDT decreased sharply.（3）TAS glasses MIR fs laser damage mainly underwent a process of material erosion,stripe formation,damage extension,and glass melting.Photoionization was the main cause of TAS glasses damage.At the beginning of damage,periodic stripe formation were generated due to the interference between the fs laser and the plasma generated by the electron excitation transition.Because the thermal diffusion coefficients of TAS glasses were small,the thermal accumulation effect was dominant for fs laser ablation of TAS glasses in the middle and late stages of damage,and the glass gradually melted and eventually covered the stripe structure.Besides,after the stoichiometric ratio glass was damaged,the Se concentration of the damaged area reduced by gasification,and the Te concentration relatively increased.