Mr. Owen Kearney Profile

Owen Kearney

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Author | Student Chapter Secretary

Publications (2)

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Proceedings Article | 24 June 2024 Presentation + Paper

Optical fabrication of micro-patterned photopolymer surfaces for application in sensing

Owen Kearney, I. Naydenova

Proceedings Volume 13015, 130150R (2024) https://doi.org/10.1117/12.3022060

KEYWORDS: Spatial light modulators, Fourier transforms, Optical lithography, Image processing, Optical surfaces, Diffraction, Atomic force microscopy, Reflection, Biological samples, Bacteria

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In the study of surface relief based diffractive sensors, surface morphology is a key parameter. There are many approaches to patterning of surfaces on the micro and nanoscale, such as lithography, self-assembly, ultra-thin alumina mask nano-surface patterning, and Scanning probe techniques. While these techniques allow for fabrication of structures with very high resolution, the development of an alternative technique that can deliver complex, easily customisable surface structures at a low cost is well justified. Two optical techniques for patterning of photopolymers of different chemical compositions will be presented and compared. They allow the fabrication of surface structures on the micron scale directly into a photopolymer layer by single step recording of the whole pattern. The first approach utilizes holographic recording with three laser beams with different states of polarization and adjusted intensities. A semi-automated optical system utilising this approach currently allows for the creation of surface relief cross-gratings (SRCG) of unit cell size ranging from 8 x 8 μm² to as small as 2 x 2 μm², but smaller features are theoretically possible. Control over surface morphology and surface roughness by optical patterning is experimentally confirmed. The second approach involves the use of a digital micro-mirror array spatial light modulator. This approach allows for the creation of surface relief with features as small as 3 μm², with higher achievable image complexity, due to the control over individual micro-mirrors. Surfaces fabricated in photopolymer materials utilising both approaches were characterised via atomic force microscopy, phase contrast microscopy, fast Fourier transform analysis of collected images, and diffraction efficiency measurements. Both approaches are compared in view of their application in diffractive optical sensors.

Proceedings Article | 31 May 2023 Presentation + Paper

Fabrication and characterisation of large area, uniform, and controllable surface relief patterns in photopolymer material

Owen Kearney, I. Naydenova

Proceedings Volume 12574, 125740D (2023) https://doi.org/10.1117/12.2665681

KEYWORDS: Diffraction, Bacteria, Polarization, Surface roughness, Diffraction gratings, Mirrors, Atomic force microscopy, Adhesion, Holography, Fourier transforms

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As the risk of antibiotic resistant pathogens increases, development of convenient point of care devices is essential. Such devices would help avoid infection – ensure cleanliness of environments and assist in bacteria analysis. The ultimate aim of the research presented here is to develop a compact, cost effective, easy to use optical device which is capable of detecting and quantifying bacteria in an aqueous sample. The surface relief patterns have a dual role, they provide a diffracted light signal, and control the adhesion of the bacteria to the surface. The strength of the diffracted signal is expected to provide a quantitative measure of the number of bacterial cells attached to the patterned surface. An adjustable holographic set up for controlled patterning of a photopolymer surface using three-beams of varying intensity, incident angles, and state of polarisation was built. The system allows for the creation of surface relief cross-gratings (SRCG) of unit cell size ranging from 8 x 8 μm² (125 lines / mm) to as small as 1 x 1 μm² (1000 lines/ mm). The surfaces are analysed via AFM, Phase contrast Microscopy, Fast Fourier transform analysis of the collected images and diffraction efficiency measurements. The surface relief amplitude dependence on recording parameters is investigated, the results demonstrate a strong dependence of the surface relief height on the period of the recorded structures. The largest surface relief amplitude achieved is 300 nm at 8 μm period. The possibility to achieve control over surface roughness by optical patterning was experimentally confirmed. The production and characterisation of large area uniform SRCG, with controllable patterns will allow further experiments aiming at the development of bacterial assays to be completed, namely SRCG contact copying in water resistant materials and their functionalisation by coating.

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