DTU Fotonik - Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark.
Institute of Optics, University of Rochester, Rochester, NY 14627-0186, United States of America.
Sci Rep. 2016 Nov 25;6:37738. doi: 10.1038/srep37738.
Nonlinear spectroscopic investigation in the terahertz (THz) range requires significant field strength of the light fields. It is still a challenge to obtain the required field strengths in free space from table-top laser systems at sufficiently high repetition rates to enable quantitative nonlinear spectroscopy. It is well known that local enhancement of the THz field can be obtained for instance in narrow apertures in metallic films. Here we show by simulation, analytical modelling and experiment that the achievable field enhancement in a two-dimensional array of slits with micrometer dimensions in a metallic film can be increased by at least 60% compared to the enhancement in an isolated slit. The additional enhancement is obtained by optimized plasmonic coupling between the lattice modes and the resonance of the individual slits. Our results indicate a viable route to sensitive schemes for THz spectroscopy with slit arrays manufactured by standard UV photolithography, with local field strengths in the multi-ten-MV/cm range at kHz repetition rates, and tens of kV/cm at oscillator repetition rates.
太赫兹（THz）范围内的非线性光谱研究需要光场的强度达到相当大的水平。从台式激光系统在足够高的重复率下在自由空间中获得所需的场强，以实现定量的非线性光谱学，仍然是一个挑战。众所周知，例如在金属膜中的窄孔中可以获得 THz 场的局部增强。这里我们通过模拟、分析建模和实验表明，与单个狭缝的增强相比，在金属膜中的具有微米尺寸的二维狭缝阵列中可以将可实现的场增强提高至少 60%。通过优化晶格模式和单个狭缝的共振之间的等离子体耦合可以获得额外的增强。我们的结果表明，通过标准的紫外光刻制造的狭缝阵列，在 kHz 重复率下的局部场强达到数十 MV/cm 范围，在振荡器重复率下达到 tens of kV/cm，对于 THz 光谱学来说是一种可行的方案。
