Foley Iv Jonathan J, Harutyunyan Hayk, Rosenmann Daniel, Divan Ralu, Wiederrecht Gary P, Gray Stephen K
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439.
Department of Physics, Emory University, Atlanta, GA 30322.
Sci Rep. 2015 Apr 23;5:9929. doi: 10.1038/srep09929.
It is widely believed that the reflection minimum in a Kretschmann-Raether experiment results from direct coupling into surface plasmon polariton modes. Our experimental results provide a surprising discrepancy between the leakage radiation patterns of surface plasmon polaritons (SPPs) launched on a layered gold/germanium film compared to the K-R minimum, clearly challenging this belief. We provide definitive evidence that the reflectance dip in K-R experiments does not correlate with excitation of an SPP mode, but rather corresponds to a particular type of perfectly absorbing (PA) mode. Results from rigorous electrodynamics simulations show that the PA mode can only exist under external driving, whereas the SPP can exist in regions free from direct interaction with the driving field. These simulations show that it is possible to indirectly excite propagating SPPs guided by the reflectance minimum in a K-R experiment, but demonstrate the efficiency can be lower by more than a factor of 3. We find that optimal coupling into the SPP can be guided by the square magnitude of the Fresnel transmission amplitude.
人们普遍认为，在Kretschmann-Raether实验中反射最小值源于直接耦合到表面等离激元极化激元模式。我们的实验结果表明，与K-R最小值相比，在分层金/锗薄膜上激发的表面等离激元极化激元（SPP）的泄漏辐射模式存在惊人差异，这一结果明显对这一观点提出了挑战。我们提供了确凿证据，证明K-R实验中的反射率下降与SPP模式的激发无关，而是对应于一种特定类型的完全吸收（PA）模式。严格的电动力学模拟结果表明，PA模式只能在外部驱动下存在，而SPP可以存在于与驱动场无直接相互作用的区域。这些模拟表明，在K-R实验中有可能通过反射最小值间接激发由其引导的传播SPP，但结果表明效率可能会降低三倍以上。我们发现，进入SPP的最佳耦合可以由菲涅耳透射振幅的平方模来引导。
