Efficient nonlinear optical frequency mixing in small volumes is key for future on-chip photonic devices. However, the generally low conversion efficiency severely limits miniaturization to nanoscale dimensions. Here we demonstrate that gradient-field effects can provide for an efficient, conventionally dipoleforbidden nonlinear response. We show that a longitudinal nonlinear source current can dominate the thirdorder optical nonlinearity of the free electron response in gold in the technologically important near-IR frequency range where the nonlinearities due to other mechanisms are particularly small. Using adiabatic nanofocusing to spatially confine the excitation fields, from measurements of the 2ω1 - ω2 four-wave mixing response as a function of detuning ω1 - ω2, we find up to 10-5 conversion efficiency with a gradient-field contribution to χ(3)Au of up to 10-19 m2/V2. The results are in good agreement with the theory based on plasma hydrodynamics and underlying electron dynamics. The associated increase in the nonlinear conversion efficiency with a decreasing sample size, which can even overcompensate the volume decrease, offers a new approach for enhanced nonlinear nano-optics. This will enable more efficient nonlinear optical devices and the extension of coherent multidimensional spectroscopies to the nanoscale.
BT - Physical Review Letters DA - 2018-05 DO - 10.1103/PhysRevLett.120.203903 N2 -Efficient nonlinear optical frequency mixing in small volumes is key for future on-chip photonic devices. However, the generally low conversion efficiency severely limits miniaturization to nanoscale dimensions. Here we demonstrate that gradient-field effects can provide for an efficient, conventionally dipoleforbidden nonlinear response. We show that a longitudinal nonlinear source current can dominate the thirdorder optical nonlinearity of the free electron response in gold in the technologically important near-IR frequency range where the nonlinearities due to other mechanisms are particularly small. Using adiabatic nanofocusing to spatially confine the excitation fields, from measurements of the 2ω1 - ω2 four-wave mixing response as a function of detuning ω1 - ω2, we find up to 10-5 conversion efficiency with a gradient-field contribution to χ(3)Au of up to 10-19 m2/V2. The results are in good agreement with the theory based on plasma hydrodynamics and underlying electron dynamics. The associated increase in the nonlinear conversion efficiency with a decreasing sample size, which can even overcompensate the volume decrease, offers a new approach for enhanced nonlinear nano-optics. This will enable more efficient nonlinear optical devices and the extension of coherent multidimensional spectroscopies to the nanoscale.
PY - 2018 T2 - Physical Review Letters TI - Enhanced Third-Order Optical Nonlinearity Driven by Surface-Plasmon Field Gradients UR - https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.203903 VL - 120 SN - 0031-9007 ER -