Characterisation of laser processed bio-compatible materials and the realisation of electro optical diffraction gratings

Aesa, Abdulsattar Ahmad

Abstract

Laser processing methods using excimer lasers have become very attractive for processing materials and the fabrication of micro and nano optical components. Diffraction gratings are used in a wide range of applications and require different fabrication methods. These components can be fabricated from a variety of biocompatible polymers. In this work, an Argon Fluoride (ArF) excimer laser operating at a wavelength of 193 nm has been used to process chitosan and agarose substrates. These materials have been characterised for differing laser processing conditions. Diffraction gratings and component demonstrators have been realised using Laser Direct writing (LDW) and nanoimprinting lithography (NIL). Characterisation of the ArF 193 nm laser work involves ablation threshold, optical absorption measurements and quantification of structural and morphological changes. This results can be used to identify the ideal laser fluence to be used for the production of a diffraction grating and similar optical components fabricated from chitosan. An ablation threshold of chitosan at 193 nm wavelength has been measured as 85 mJcm⁻² and an optical absorption coefficient of 3×10³ cm⁻¹.

A diffraction grating structure, measuring 12 μm, was generated in biocompatible materials films; chitosan and agarose, using a laser processing method. The results showed that the interaction between the laser and these materials can potentially open the pathway for a wide range of practical, real world applications such as optical and biomedical applications. Diffraction gratings with a feature size of 1 μm were successfully formed on the biocompatible material free standing films using a NIL technique. Microstructure cross grating patterning made of chitosan and agarose have been fabricated by ArF excimer laser processing using a mask projection ablation technique. Temperature rise calculations have been carried out by COMSOL™ Multi-Physics v5.3 using a Finite Element Method (FEM), to predict the temperature rise during laser ablation processing of chitosan and agarose. In addition, COMSOL™ Multi-physics v5.3 has been used to simulate the electric field in the vicinity of a diffraction grating that is illuminated with light from a HeNe laser emitting at a wavelength of 632.8 nm.

The final experimental work investigated the possibility of realising 5CB liquid crystal doped chitosan diffraction gratings doped with Sudan Black B (SBB) dye to enhance the absorption properties at 632.8 nm. Diffraction gratings was fabricated using two intersecting beams from a HeNe laser. Polymer Dispersed Liquid Crystal (PDLC) chitosan doped with 5CB and SBB dye diffraction gratings were experimentally characterised.

Citation

Aesa, A. A. (2018). Characterisation of laser processed bio-compatible materials and the realisation of electro optical diffraction gratings. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4221019

• Thesis Type: Thesis
• Deposit Date: Nov 13, 2018
• Publicly Available Date: Feb 23, 2023
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/4221019
• Additional Information: Department of Physics and Mathematics, The University of Hull
• Award Date: Aug 1, 2018