Subwavelength Imaging Near Field Lenses
| Autor: | Dzung-Han Tsai, 蔡宗翰 |
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| Rok vydání: | 2008 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 The research of slab lens attracts tremendous attention since 2000. Specially designed slab lens made of appropriate materials can gather evanescent waves and focus light to form subwavelength images, thus the imaging efficiency can be improved substantially. Up to now, most researches concerning slab lens are about improving the imaging efficiency and increasing the object-image distance, and the discussions about the relations between the object distance and image distance are rare or lacking. In this thesis, we study the imaging properties of slab lens consisting of periodically arranged metal and dielectric layers. The metal and dielectric are chosen as Ag and Si3N4, respectively. We explore the influences of varying the thickness ratio between the metal layer and dielectric layer as well as the relations between the object distance and image distance. Using transfer matrix method (TMM), the band structures and the field patterns of the propagating modes can be obtained, and the electromagnetic fields in every layer under the illumination of incident light can be calculated. We first predict the propagating direction of the energy flow according to the constant frequency curve of the band structure, and then we compare the prediction with the numerical result of the simulation for electromagnetic waves. The wavelength of the light source is chosen as 363.6 nm, and the source pattern is a normally incident Gaussian beam, having a full width at half maximum (FWHM) of 1/10 wavelengths. The slab lens consists of 5 silver layers and 4 Si3N4 layers. In one period, the total thickness of one sliver layer and one Si3N4 layer is 80nm, with thickness ratio from 1:9 to 9:1. The source is located from the input edge of the slab lens at a distance smaller than one wavelength. Our numerical simulations reveal that: 1. continually varying the object distance, the maximum distance for forming subwavelength image changes following the same direction as the object moves, and the image distance increment is the same as the moving distance of the object. 2. Shifting both the object and the imaging plane towards the same direction and distance, the normalized image profile keeps unchanged. The results obtained in this thesis can provide the theoretical bases for experimental tests of the imaging behaviors of the slab lens. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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