Research and Development of a Sub-wavelength Nondiffracting Beam Laser Writer: Theory and Fabrication of Nano-optical Components to System Verification
Date Issued
2009
Date
2009
Author(s)
Cheng, Tsung-Dar
Abstract
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.
Subjects
nondiffracting beam
nano optics
optical head
high-aspect-ratio structure
Bessel beam writer
Type
thesis
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