次波長超長焦深光束直寫儀的研究與開發：從奈米光學元件的理論與製造到系統性能驗證之研究

Research and Development of a Sub-wavelength Nondiffracting Beam Laser Writer: Theory and Fabrication of Nano-optical Components to System Verification

鄭琮達(Tsung-Dar Cheng)

指導教授 ： 葉超雄 ； 李世光

國立臺灣大學/工學院/應用力學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.10035

摘要

傳統光學系統受限於繞射極限，為了追求更小的聚焦光點，焦深將迅速縮小到接近一般試片的表面粗糙度。另一方面，Durnin在1987年首先提出無繞射光束的概念，此光束的焦深比一般透鏡聚焦光束大數十至數百倍。然而，其聚焦光點仍無法達到次微米甚至是次波長等級。
拜微機電技術進步之賜，次波長光學元件研究如雨後春筍般蓬勃發展。其中，表面電漿光學就是其中一例。本論文利用次波長結構結合表面電漿光學設計新型光學元件。文中提出結合金屬次波長結構與發光二極體產生長焦深次微米聚焦光點，以及利用銀和鎢的次波長圓環光學頭結合不同入射偏極態產生各種次波長無繞射光束，並提出一種新型貝索光束直寫儀，整合基礎物理研究以及光機設計，製作出具有超長焦深次波長光束，可應用於直接刻寫出高深寬比結構。
模擬方面提出了完整的模擬流程，包括利用嚴格耦合波理論快速估算出射光指向角，利用叢集電腦進行三維有限差分法模擬，並利用數值方法得到柱狀表面電漿子之色散曲線。模擬結果與實驗有良好的一致性。這些模擬不僅可幫助我們用來預測未知的物理現象，更可以提供我們設計的相關參數。
光機設計中，利用了電腦輔助設計軟體對結構進行配置與模擬，結合所設計之次波長圓環光學頭，產生次波長無繞射光束。為了達到自動化圖形刻寫，利用了圖形控制程式與被控元件整合，透過適當的校正流程，能夠使系統得到最佳的曝光效果。
實驗方面，我們使用倒立式顯微鏡觀測指向性出射的現象，並使用近場光學顯微鏡量測次波長圓環結構的近場及遠場特性。不但發現銀次波長圓環結構能夠依照不同的圓環材質與入射偏極態產生不同的類次波長無繞射光束，其出射光具有高穿透能量、次波長聚光點、及長焦深等特性。結合貝索光束直寫儀，成功地在AZP4620正光阻上製作出線寬為1 μm、深寬比達到5:1的高深寬比結構。

關鍵字

無繞射光束 ； 奈米光學 ； 光學頭 ； 高深寬比結構 ； 貝索光束直寫儀

並列摘要

Traditional optical systems are affected by diffraction limit which its focal spot size is limited by the incident wavelength and numerical aperture of the system. In 1987, Durnin and the coworkers firstly demonstrated the concept of nondiffracting beam which its depth of focus was larger than traditional Gaussian beam 10 to 100 times. However, the minimum spot size of nondiffracting beam still remained in the range of several microns.
In thesis, we demonstrate the simulations and numerical calculations of beaming light from bull’s eye structure and SAA optical head. We also performed experiments to verify the optical properties and feasibilities of optical head continuously. A Bessel beam writer system which is integrated with SAA optical head is designed and performed the ability of fabricating high-aspect-ratio structure on photoresist.
We examine the optical properties such as propagation modes, focal length, sidelobes, etc. of metallic sub-wavelength annular apertures (SAA) and use finite-difference time-domain (FDTD) simulation to compare our experimental findings. Using two different metals, silver and tungsten, we examine the different optical transmission properties of the two metallic SAA structures. The far-field propagation of the silver SAA structure is found to be a type of quasi-Bessel beam when compares with a quasi-Bessel beam generated by a perfect axicon. The propagation characteristics of these two beams were found to match qualitatively. The far-field transmitted light generated by the silver SAA structure is found to possess a 390 nm sub-micron focal spot with a 24 μm depth of focus, which is much smaller than the focal spot generated by a perfect axicon. We also find that a tungsten SAA structure can generate a sub-micron quasi-Mathieu beam. Utilizing radially polarized and azimuthally polarized beam, we can generate higher-order quasi-Bessel beam from SAAs. We use Bessel beam writer system to fabricate the high-aspect-ratio structure on AZP4620 positive photoresist with 1 μm line width and aspect ratio 5:1.

並列關鍵字

nondiffracting beam ； nano optics ； optical head ； high-aspect-ratio structure ； Bessel beam writer

參考文獻

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