4th Physics Institute and Research Center SCoPE, University of Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany.
Nano Lett. 2015 Jun 10;15(6):3917-22. doi: 10.1021/acs.nanolett.5b00747. Epub 2015 May 15.
We perform second harmonic spectroscopy of aluminum nanoantenna arrays that exhibit plasmonic resonances at the second harmonic wavelength between 450 and 570 nm by focusing sub-30 fs laser pulses tunable from 900 to 1140 nm onto the nanoantenna arrays. We find that a plasmonic resonance at the second harmonic wavelength boosts the overall nonlinear process by more than an order of magnitude. In particular, in the measurement the resonant second harmonic polarization component is a factor of about 70 stronger when compared to the perpendicular off-resonant second harmonic polarization. Furthermore, the maximum of the second harmonic conversion efficiency is found to be slightly blue-shifted with respect to the peak of the linear optical far-field spectrum. This fact can be understood from a simple model that accounts for the almost off-resonant absorption at the fundamental wavelength and the resonant emission process at the second harmonic.
我们通过将可调谐范围在 900 至 1140nm 之间的亚 30fs 激光脉冲聚焦到纳米天线阵列上，对在 450 至 570nm 之间的二次谐波波长处表现出等离子体激元共振的铝纳米天线阵列进行二次谐波光谱测量。我们发现，二次谐波波长处的等离子体激元共振将整体非线性过程提高了一个数量级以上。特别是在测量中，与垂直于共振的二次谐波偏振相比，共振二次谐波偏振分量要强约 70 倍。此外，二次谐波转换效率的最大值相对于线性远场光光谱的峰值略有蓝移。从一个简单的模型可以理解这一事实，该模型考虑了基波处的几乎非共振吸收和二次谐波处的共振发射过程。
