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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

High-resolution and large-area laser interference nanomanufacturing technology

Wang, Dapeng January 2014 (has links)
The thesis systematically investigates the laser interference nanomanufacturing technology taking into account its advantages and abilities to realise various potential applications. The latest progresses have addressed the major issues hampering the cross-scale developments of structural applications, such as cost-ineffective fabrication, limited area, low efficiency and challenging integration. The studies carried out on high-resolution and large-area laser interference nanomanufacturing technology will complement the exploration of modern optical devices and extraordinary functional applications. With respect to classical interference theory and relevant references, there is still a lack of studies providing insight into the effects of polarisation on the multi-beam interference while it is found that the polarisation vector plays a key role in the formation, period and contrast of interfering patterns. Herein, the theory of multi-beam interference is developed through the integration of the polarisation vector and electric field vector. It is worth pointing out that based on the detailed analysis of the four-beam interference with the special polarisation modes, it is demonstrated that the modulation phenomenon in four-beam laser interference is the result of the misalignment of incident angles or unequal incident angles only in the case of the TE-TE-TM-TM mode. In the experiments, a straightforward method of generating various well-defined structures on material surfaces is proposed using the nanosecond laser interference system. The experimental results of two-, three- and four-beam interference show a good correspondence to the theoretical analyses and simulations. Artificial bio-structures are fabricated using the four-beam interference method with the TE-TE-TE-TE polarisation mode and the fabricated microcone structures exhibit excellent properties with both a high contact angle (CA=156.3°) and low omnidirectional reflectance (5.9-15.4%). In order to fabricate high-resolution structures, the 266nm nanosecond laser interference system is employed to treat the organic and metal-film materials. Nanograting structures with feature sizes of sub-100nm width and 2nm height are fabricated on the organic material surface. An attempt is successfully conduced to produce the nanoelectrode arrays by using laser interference lithography and chemical deposition. Finally, the advantages of the developed laser interference technology and contributions of the research are summarised, and recommendations of future work are given.
2

3D Printing of Nanoantenna Arrays for Optical Metasurfaces

Jithin Prabha (5930795) 17 January 2019 (has links)
Additive manufacturing using 2 photon polymerization is of great interest as it can create nanostructures with feature sizes much below the diffraction limit. It can be called as true 3D printing as it can fabricate in 3 dimensions by moving the laser spot in any 3D pattern inside the resist. This unique property is attributed to the non-linearity of two photon absorption which makes the polymerization happen only at the focal spot of the laser beam. This method has a wide range of applications such as optics/photonics, metamaterials, metasurfaces, micromachines, microfluidics, tissue engineering and drug delivery.<br>This work focuses on utilizing 2 photon fabrication for creating a metasurface by printing diabolo antenna arrays on a glass substrate and subsequently metallizing it by coating with gold. A femtosecond laser is used along with a galvo-mirror to scan the geometry inside the photoresist to create the antenna. The structure is simulated using ANSYS HFSS to study its properties and optimize the parameters. The calculations show a reflectance dip and zero reflectance for the resonance condition of 4.04 μm. An array of antennas is fabricated using the optimized properties and coated with gold using e-beam evaporation. This array is studied using a fourier transform infrared spectrometer and polarization dependent reflectance dip to 40% is observed at 6.6 μm. The difference might be due to the small errors in fabrication. This method of 3D printing of antenna arrays and metallization by a single step of e-beam evaporation is hence proved as a viable method for creating optical metasurfaces. Areas of future research for perfecting this method include incorporating an autofocusing system, printing more complicated geometries for antennas, and achieving higher resolution using techniques like stimulated emission depletion.

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