The on-demand modulation of defects in materials for the effective modulation of optical nonlinearity is desirable,while it remains a great challenge.In this work,we demonstrate that electrochemical activation is a fa...The on-demand modulation of defects in materials for the effective modulation of optical nonlinearity is desirable,while it remains a great challenge.In this work,we demonstrate that electrochemical activation is a facile and convenient approach to modulating the broadband third-order nonlinear absorption of nanoporous tungsten oxide(WO3-x)thin film.The film does not exhibit optical nonlinearity at the initial state,while shows a distinct saturable absorption under an applied voltage of-2.5 V with the excitation of 515,800,and 1,030 nm laser.The nonlinear absorption coefficient(β_(eff))is-766.38±6.67 cm·GW^(-1) for 1,030 nm laser,-624.24±17.15 cm·GW-1 for 800 nm laser,and-120.70±11.49 cm·GW^(-1) for 515 nm laser,and the performance is competitive among inorganic saturable absorbers.The activation is accomplished in 2 min.The performance enhancement is ascribed to the formation of abundant in-gap defect states because of the reduction of the tungsten atoms,and a Pauli-blocking effect occurs during the excitation of in-gap defect states.The small feature size of WO_(3-x)(-12 nm)enables the effective and fast introduction and removal of the defects in porous film,and accordingly the fast and broadband modulation of optical nonlinearity.Our results suggest a controllable,effective,and convenient approach to tuning the nonlinear absorption of materials.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51772214,51432006,and 51701170)the Ministry of Science and Technology of China(No.2011DFG52970)+2 种基金the Ministry of Education of China(IRT14R23),111 Project(No.B13025)the Innovation Program of Shanghai Municipal Education Commission,the national youth talent support program(No.W03070073)the project of science and technology plan of Fujian Province(No.2018J01520).
文摘The on-demand modulation of defects in materials for the effective modulation of optical nonlinearity is desirable,while it remains a great challenge.In this work,we demonstrate that electrochemical activation is a facile and convenient approach to modulating the broadband third-order nonlinear absorption of nanoporous tungsten oxide(WO3-x)thin film.The film does not exhibit optical nonlinearity at the initial state,while shows a distinct saturable absorption under an applied voltage of-2.5 V with the excitation of 515,800,and 1,030 nm laser.The nonlinear absorption coefficient(β_(eff))is-766.38±6.67 cm·GW^(-1) for 1,030 nm laser,-624.24±17.15 cm·GW-1 for 800 nm laser,and-120.70±11.49 cm·GW^(-1) for 515 nm laser,and the performance is competitive among inorganic saturable absorbers.The activation is accomplished in 2 min.The performance enhancement is ascribed to the formation of abundant in-gap defect states because of the reduction of the tungsten atoms,and a Pauli-blocking effect occurs during the excitation of in-gap defect states.The small feature size of WO_(3-x)(-12 nm)enables the effective and fast introduction and removal of the defects in porous film,and accordingly the fast and broadband modulation of optical nonlinearity.Our results suggest a controllable,effective,and convenient approach to tuning the nonlinear absorption of materials.