利用遠離式光柵提升奈米光學天線之場強

Electric Field Enhancement of Optical Nanoantennas Using Remote Grating

梁硯翔(Yen-Hsiang Liang)

指導教授 ： 李佳翰

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.10365

摘要

近年來，表面增強拉曼散射的研究引起了相當多的應用議題。舉例來說，相關應用指出收集表面波可於光學天線內形成更強之局域性電場強度。藉由光學天線的發展能進一步提升表面增強拉曼散射訊號強度。在這項研究中，我們提出了利用遠離式光柵結構在金屬薄膜和介電材料間形成表面波，並藉由光學天線收集金屬表面上的表面波增強其場強。在此，光學天線可以產生窄頻的共振和增強電場強度效果。此外，我們藉由時域有限差分法分析了物理機制和不同參數的功能並且最佳化結構得到最大場強。其後，比較菲涅耳波帶片光柵和遠離式光柵，其菲涅耳波帶片光柵可以將光聚焦到光學天線，但是沒有完全激發表面波，所以強度比遠離光柵結構增強學天線來的弱。在實驗製程及量測方面，考慮半導體製程可行性之下，我們提出可以利用電子束微影製作簡單式遠離式光柵結構，且規劃光譜儀實驗架構量測其光訊號穿透及反射率等數值，做為進一步分析。

關鍵字

時域有限差分 ； 表面電漿子 ； 光學天線 ； 遠離式光柵 ； 表面增強拉曼散射 ； 菲涅耳波帶片

並列摘要

Recently, surface-enhanced Raman scattering (SERS) has attracted more and more attentions because of its various applications. For example, the optical nanoantenna can be used for enhancing stronger localized electric field intensity by collecting the surface waves. It can promote the coupling efficiency and increase the SERS signals as well. In this research, we used the concept to excite the surface plasmons on the interface bettwen the metallic and dielectric masterials by using the remote grating structures and then the light energy can be collected into the optical nanoantenna on the metallic surface. It generates narrow bandwidth resonances and stronger electric field intensity in the gap of nanoatennas. By using the Lumerical FDTD Solutions software, we studied the physical mechanism by analyzing the numerical simulations and tuned different parameters for optimizing the structures to have stronger field enhancements. Furthermore, we replaced the remote grating to the Fresnel zone plate grating, which can focus light into optical nanoantenna, but the field enhancements for the cases of Fresnel zone plate gratings are not better than the cases of remote grating structures because the surface waves can not be excited by the Fresnel zone plate gratings. The remote grating structures can be fabricated by the E-beam lithography and semiconductor fabrication procedures. In future work, the optical transmission and reflection of the fabricated samples can be measured by the spectrometer.

並列關鍵字

FDTD ； plasmonics ； optical nanoantenna ； remote grating ； SERS ； Fresnel zone plate

參考文獻

[1] R. W. Wood, "On a Remarkable Case of Uneven Distribution of Light in a Diffraction Grating Spectrum," Proceedings of the Physical Society of London 18, 269 (1902).

[2] R. H. Ritchie, "Plasma Losses by Fast Electrons in Thin Films," Physical Review 106, 874-881 (1957).

[3] E. Kretschmann, and H. Raether, "Radiative decay of nonradiative surface plasmons excited by light," Z. Naturforsch. A 23, 2135 (1968).

[4] A. Otto, "Excitation of nonradiative surface plasma waves in silver by the method of frustrated total reflection," Z. Physik 216, 398-410 (1968).

[5] S. Park, G. Lee, S. H. Song, C. H. Oh, and P. S. Kim, "Resonant coupling of surface plasmons to radiation modes by use of dielectric gratings," Optics Letters 28, 1870-1872 (2003).