以連續數值孔徑模式陳述次波長圓環光學效應的適切性研究

Experiement and simulation on the continuous numerical aperture proposition of sub-wavelength annular aperture

方俊傑(Chun-Chieh Fang)

指導教授 ： 李世光 ； 吳光鐘

國立臺灣大學/工學院/應用力學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.02545

摘要

在1959年Richard 和 Wolf 這兩位科學家調整雷射的共振腔而產生了放射狀(radial)偏極光束，由於放射偏極光束具有特殊的電場特性，因此在這些年來放射偏極光束被廣泛的討論及應用。
在本研究團隊的先前研究中，發現利用次波長的圓環結構在線偏極態的入射光情況下可以產生長景深的零階貝索光束(Bessel beam)，而在我的研究中我嘗試將放射偏極態以及方向(azimuthal)偏極態的雷射光入射到次波長圓環結構，發現可以產生一階的貝索光束，而所產生的聚焦光點遠比之前利用其他方法產生來的小，並且達到次波長的等級。
由於方向偏極態光束的聚焦電場可以分為縱向以及橫向偏極態，因此焦點的電場分佈以及聚焦圖形都會與該聚焦的光學元件之數值孔徑有很密切的關係，此一特性在本文的研究過程中發生了很大的效應，並因而針對次波長圓型結構可以產生長景深此特性提出此元件為具有連續數值孔徑之光學元件的看法。經由比較傳統的高斯透鏡以及此次波長光學元件，本文說明了次波長圓環結構聚焦特性與數值孔徑的關係，同時也提出了次波長圓環結構在放射偏極態光束入射時聚焦電場的數學模型。

關鍵字

表面電漿 ； 次波長結構 ； 貝索光束 ； 輻射狀偏極態 ； 連續數值孔徑

並列摘要

The three-dimensional electromagnetic field dispersion of focused beam is an important issue for optical applications. Since 1959, Richard and Wolf had generated radially polarized (RP) beam by optical mechanism. After that, radial vector beam has attracted a great deal of discussions in recent years.
Using sub-wavelength annular aperture (SAA) structure is a brand new method to generate non-diffraction doughnut beam. When the RP beam is focused by SAA structure, the focused RP beam in free space was found to propagate in the J1 Bessel beam format, Both simulation and experimental results showed that sub-wavelength focal spot and long depth of focus were achieved in the above-mentioned combinations.
The electric field at focal plane of RP beam can be separated into longitudinal and transverse components. Due to their features and different intensity distribution, there are special phenomena in the electrical field at focus. For example, the intensity ratio of longitudinal and transversal component are found to be related to the numerical aperture (NA) of focal lens used and the focal pattern also depends on NA.
For the long depth of focus of SAA structure by RP beam incidence, we proposed that SAA structure is a continuous numerical aperture (NA) optical element. To verify this proposition, we compared the properties of SAA structure with the traditional objective lens illuminated by RP beam.

並列關鍵字

surface plasmon ； sub-wavelength structure ； Bessel beam ； radial polarization ； continuous numerical aperture

參考文獻

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