Cardiff University School of Physics and Astronomy, The Parade, Cardiff, UK.
Phys Chem Chem Phys. 2013 Mar 28;15(12):4226-32. doi: 10.1039/c2cp43451b.
Using a phase-sensitive degenerate four-wave mixing technique in heterodyne detection we measured the ultrafast changes of the complex polarizability in single gold nanoparticles at the surface plasmon resonance. Two components in the nanoparticle nonlinear response are distinguished, depending on the linear polarization direction of pump and probe pulses and particle geometry. One component is quantitatively modeled as the variation of the complex dielectric constant induced by the initial increase in the electron gas temperature following the absorption of the pump pulse, and the subsequent electron thermalization with the lattice and the surrounding. The dependence of the measured four-wave mixing on the probe field polarization direction is well reproduced by including a deviation from spherical symmetry in the nanoparticle dielectric constant. The second component manifests as a significant increase in the measured nonlinearity when the probe field is co-polarized with the pump field at pump-probe time overlap. We attribute this component to the nonlinear response from coherent surface plasmons before dephasing into single electron excitations.
我们使用相位敏感简并四波混频技术在外差检测中测量了单个金纳米粒子在表面等离激元共振处的复介电常数的超快变化。根据泵浦和探测脉冲的线性偏振方向和粒子几何形状，纳米粒子非线性响应的两个分量得以区分。其中一个分量被定量地建模为吸收泵浦脉冲后电子气温度初始升高所引起的复介电常数的变化，以及随后与晶格和周围环境的电子热化。通过在纳米粒子介电常数中引入偏离球对称性，可以很好地再现测量的四波混频对探测场偏振方向的依赖关系。第二个分量表现为当探测场与泵浦场在泵浦-探测时间重叠时同偏振时，测量的非线性度显著增加。我们将此分量归因于相干表面等离激元的非线性响应，然后退相为单个电子激发。
