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.