Giant and Tunable Optical Nonlinearity via In Situ Electrochemical Control of the Tellurium–Electrolyte Interface

The semiconductor–electrolyte interface with strong electrical tunability offers a platform for tuning nonlinear optical (NLO) processes and achieving giant optical nonlinearities. However, such a demonstration and fundamental mechanistic understanding of electrochemically tuned NLO properties have not been reported. Here, we developed an in situ electrochemical Z-scan system to characterize the evolution of NLO responses in tellurium nanorod films under bias voltage. Nonlinear absorption (β) and refraction (n2) indexes change from −6575 cm/GW and −0.238 cm2/GW at −0.3 V to −12500 cm/GW and −0.390 cm2/GW at 0.3 V, displaying diode-like rectification characteristics. Macroscopically, this tunable third-order nonlinear susceptibility (χ̃(3)) mainly arises from the contribution of fourth-order nonlinear susceptibility (χ̃(4)E) under an electric field. Microscopically, the voltage-controlled band bending modulates carrier density, absorption cross-section, and relaxation time, thereby tuning nonlinear absorption and refraction. Our work demonstrates an electrochemical tuning strategy that enables giant and broadly tunable optical nonlinearity in nanomaterial systems.