Tailoring Of Refractive Index And Thermo-optic Coefficient In Chalcogenide Glasses

Chalcogenide glasses are amorphous mateirals based on chalcogen elements(e.g.S,Se and Te).They have excellent infrared transparency,high linear and nonlinear refractive indices,low phonon energy and tunable photosensitivity,and therefore have been extensively studied for infrared opitcs,nonlinear photonics and infrared lasers.In optical designs,linear refractive index(n)of the glass and its thermo-optic coefficient(ζ)are crucial parameters.However,there is little systematic study on the n and dn/dt of chalcogenide glasses,mainly due to the limit of the testing technique and the measurement accuracy.In this thesis,Ge-As-Se and Ge-Sb-Se chalcogenide glasses,which are suitable for commercialization,are chosen for the study.Glasses with different topological network structure(characterized by mean coordination number,MCN or <r>)and chemical stoichiometry(characterized by the departure from stoichiometry of the composition,dSe)are synthesized.The micro-structures of the glasses are studied by Raman technique.The correlations between the property parameters such as n,ζ,density(d),and volume thermal expansion coefficient(β),and <r>,as well as dSe,are investigated.The main results obtained are as follows.(1)Ge-As-(Sb)-Se glasses have a network structure with crosslinking [GeSe4] tetrahedra and [AsSe3]([SbSe3])pyramids forming the backbone.No evident homopolar bonds are observed in the glasses with stoichiometric composition;when Se is rich,Se chains and rings are formed;when Se is deficient,As-As(Sb-Sb)and Ge-Ge homopolar bonds appear in the sturcure.(2)In Ge-As(Sb)-Se glasses,the n broadly increases with increasing d of the glasses;and the ζ decreases approximately linearly with increasing β of the glasses.In Ge-As-Se glasses,the β decreases with increasing <r>;the d shows a maximum at the stoichiometric composition(dSe=0)when Ge content is fixed;while it exhibits a minimum at...