Date of Award
Master of Science (MS)
Nature exhibits numerous creature surfaces with interesting functionalities, such as tunable colors, improved wettability, and adhesivity. These functions are induced by multi-scale surface structures. To mimic these surface functionalities for engineering applications, it is important to create multi-scale surface structures on engineering materials. Ultrafast lasers have been proven to be capable to create micro- and nano-scale structures, such as nano-ripples, microholes, conical structures, and nanoparticles, on a variety of materials including metals, polymers, dielectrics, etc. These structures are responsible for enabling different surface functionalities like superhydrophobicity, superhydrophlicity, optical property modification, improved tribological properties, and enhanced heat transfer.
Laser-induced surface structures can modify surface optical property due to the surface diffraction, which can be used for color display applications, generating anti-counterfeiting marks, and decorative purposes. Among these surface structures, sub-micron ripple-like structures responsible for the structural color effect known as Laser-induced periodic surface structure (LIPSS) are of interest to the research community. In particular, the structural color effect and LIPSS morphology on stainless steel have been widely studied. However, the unidirectionality of color effect displayed by LIPSS limits its potential application. A new two-dimensional (2D) LIPSS has been discovered to overcome this limitation, and a double-pulse method has been proposed to fabricate 2D LIPSS on stainless steel. Preliminary studies have shown that 2D LIPSS demonstrate the structural color effect without the unidirectionality as seen in regular LIPSS. However, the manufacturing method requires complex setup and alignment, which is not suitable for industrial applications. The first topic of this thesis is to develop a novel double-scanning method to fabricate 2D LIPSS on stainless steel. The mechanism of 2D LIPSS formation has been explored. A hypothesis related to the dependence of LIPSS direction on laser polarization direction has been made and validated. The developed new method does not require complex setup and is easy to be conducted for industrial applications.
Unlike metals that are widely studied for functional property modification, dielectrics remain largely unexplored when it comes to laser-induced sub-micron structures and associated surface property modification. In this work, we explore different periodic surface structures induced on fused silica by ultrafast laser irradiation and study the optical property modifications associated with them. It is revealed that several types of surface structures can be fabricated on fused silica by different processing conditions. A new type of structure that was never reported before is obtained by laser scanning mode. Possible formation mechanisms have been also been proposed for this new structure. The optical effects associated with all of these laser-induced surface structures have been studied and the relationship between the processing conditions, surface structures, and the optical effects has been established.
Limaye, Shreyas Vinay, "Study of Ultrafast Laser-Induced Surface Structures on Stainless Steel and Fused Silica for Optical Property Modification" (2020). All Theses. 3403.