Paviršinių difrakcinių elementų optimizavimas ir formavimas femtosekundiniais UV lazerio impulsais /

One of the most widely used devices in modern science and technology is the diffraction grating. Traditional methods of manufacturing diffraction gratings, such as etching, lithography, and others, face various challenges, including limited design capabilities and high costs. With the advancement of laser technologies and the availability of femtosecond solid-state lasers, these lasers can be applied to the formation and processing of various microstructures. The radiation from such lasers has a Gaussian intensity distribution, resulting in Gaussian-shaped damage during laser ablation. By periodically arranging such damage using direct laser writing, diffraction gratings can be manufactured. In this work, the simulation of single-level two-dimensional diffraction gratings was carried out using the "RSoft" software's "DiffractMOD" module, which employs the RCWA model. This was done to determine whether the laser ablation method is suitable for the efficient production of diffraction elements and to assess the diffraction efficiencies that can be achieved from single-level two-dimensional diffraction gratings manufactured using laser ablation. The simulation results indicate that it is possible to achieve approximately 30% efficiency in the zeroth order and about 10% efficiency in the first diffraction order. These results were obtained with a pit depth of 800–850 nm and a 17% pit overlap. These crater parameters can be realized using UV femtosecond laser ablation. Additionally, the theoretical modelling results show that to maintain the desired diffraction grating efficiency, it is important to control the pit depth with ~100 nm precision and to maintain pit contact or overlap up to ~25%. To verify the simulation results, an experiment was conducted in which diffraction gratings were produced using femtosecond UV laser pulses. During the experiment, attempts were made to achieve the best efficiencies by optimizing the parameters of the pits that make up the gratings. The efficiency results correspond to the trends of the theoretical model, with the highest efficiency values achieved with ~20% overlap. Efficiencies reached up to 40% in the zeroth order and 13% in the first diffraction order, with a pit depth of 0.42 µm and ~15% overlap. Under certain conditions during the experiment, up to 2.5 times higher efficiency was observed than predicted by the theoretical model. This can be explained by the formation of more complex-shaped craters rather than Gaussian-shaped craters, indicating that the laser ablation method can create more complex crater shapes, significantly increasing diffraction efficiency.

Grantor dc:publisher

Institutional Repository of Vilnius University

Year dc:date

2024

Author dc:creator

• Kniukšta, Paulius,

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

lit

Repository record dc:identifier

https://repository.vu.lt/VU:ELABAETD210578384&prefLang=en_US

OAI identifier oai:identifier

oai:vu.lt:elaba:210578384