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• W2790595912 abstract "The progress in the physics of interaction of electromagnetic radiation with matter and related fundamental processes largely benefits from the contribution of the laser sources and many areas of investigation just commenced after the breakthrough given by the realization of the first pulsed laser in 1960 by T. H. Maiman. Contactless processing and high localization of energy possibly achieved with laser processing increased its acceptance in diverse fields. In general, reduced pulse duration offered by ultrashort laser pulses is utilized for direct monitoring of temporal dynamics of several fast atomic processes. On the other hand, the high intensity provided by such pulses gives a new twist in the field of laser ablation of materials. Study related to fundamental aspects of laser interaction and ablative processes opened numerous investigations and many possible applications. Because of the ultrashort duration, fs laser holds the capacity to achieve ablation with considerably less heat effected zone which in turns provides maximum spatial resolution in term of material processing. Controlled ablation processes with fs laser offer the possibility to generate periodic surface structures with a periodicity much less than the laser wavelength. This further proves the fs laser as a precise and versatile tool for micro- and nano-fabrication processes with great accuracy. Since many surface properties of solids (optical, wetting, mechanical etc.) are closely associated to their morphology, such phenomenon can have great impact on a variety of applications. Further applications include generation of microfluidic channels for biological uses and optical integrated circuits for quantum applications.This thesis describes surface processing of crystalline silicon (100 orientation) with fs laser pulses with Gaussian as well as with some modified beam generated by a special optical device called q-plate. The experimental details and results are discussed in five chapters, which include a brief introduction about laser ablation and ultrafast laser processing. The first chapter gives a brief introduction about laser-matter interaction, underlying mechanisms of material ablation with ultrashort laser pulses along with a short overview of characterization methods used in laser induced plasma and material removal analyses. The material removal by the laser irradiation results in the generation of specific surface structures, generally called laser induced periodic surface structures (LIPSS). This chapter discusses also some basic aspects in the formation of LIPSS generated with Gaussian and Optical Vortex (OV) beams reported earlier. Finally, a short section illustrates the experiments on laser surface structuring using Gaussian and OV beams presented in the next chapters of this thesis. The second chapter deals with experimental methods used in fs surfaces structuring experiments during this thesis. In particular, the laser sources and the method used to generate OV beams using q-plate are discussed. Moreover, it includes a brief description of sample material, optical setup and instrumentations used for surface structuring with different kind of fs laser beams and surface characterization. Chapter 3 illustrates experimental results on the various surface structures generated on crystalline silicon (100) by irradiation with fs laser pulses having a Gaussian spatial intensity profile. In particular, characteristic effects related to the number of pulses and energy are described. Moreover, bending and bifurcation phenomena characterizing quasi-periodic structures are presented. These aspects are, then, rationalized in the frame of a model of surface structure formation based on surface scattered wave theory. Finally, results of some experiments on the effect of the ambient gas pressure on the surface structures are also illustrated. The fourth chapter is dedicated to surface structuring with fs OV beam with orbital angular momentum (OAM) m=1 generated by a q-plate (q=+1/2). OV beams with azimuthal, radial, spiral and linear state of polarization (SoP) in the transverse plane are employed in the process, which enables not only to generate complex surface patterns but also to characterize the OV beam itself in the focal point. Interaction with more complex OV as the one generated with additional λ/4 wave plates gives interesting patterns of ripples and grooves. Results showing the laser structuring with higher OAM beams, such as m=2 and 5, are also included in order to demonstrate the ability of laser induced structures in following the much more complex beam polarization pattern. The fifth chapter addresses an experimental investigation on direct femtosecond laser surface structuring with a higher class of vector beams generated by electrically tuning the optical retardation of a q-plate with q=+1/2. This allows generating a family of ultrashort laser beams with a continuous spatial evolution of polarization and fluence distribution in the focal plane by controlled coherent superposition of a uniformly polarized Gaussian beam with an OV beam. The use of these generalized vector beams in laser structuring can considerably improve the possibility of achieving a number of asymmetric surface patterns. Finally, a brief summary of the experimental findings is reported in the last chapter also shortly addressing the scope of surface structuring and the possible applications of process and resulting periodic surface structures formed." @default.
• W2790595912 created "2018-03-29" @default.
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• W2790595912 date "2017-04-06" @default.
• W2790595912 modified "2023-09-23" @default.
• W2790595912 title "Ultrafast laser surface structuring with Gaussian and Optical Vortex beam" @default.
• W2790595912 doi "https://doi.org/10.6093/unina/fedoa/11550" @default.
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