| Abstract |
In recent years micro- and nano- technologies have emerged as key field of study for our modern societies and way of living. Surface response to ultra-short laser pulses has been studied extensively in metals, semiconductors and dielectrics for several decades as material processing with lasers is of high industrial significance due to widespread applicability to a great number of areas like microelectronics, biomedicine, telecommunications, optical technologies and many others.
In particular, plenty of micro-electronic devices are consisted of multi-layer films, combining materials taking advantage of their optical/mechanical/thermal properties. Some examples are M-S contact, MOS technologies or engineering applications such as hot -cold mirrors, microwave attenuator chips and many others.
In addition to these, surface structure modification has been at the focus for several decades as hundreds of applications occur from artificially structured surfaces. (For example surfaces of Silicon that qualitatively and quantitatively mimic both the structure and the water repellent characteristics of the natural Lotus leaf, or structures of high significance in biomedicine for tissue repair and engineering)
All these applications occur from the fact that laser-matter interaction is highly dependent on a plethora of parameters, related both to the laser characteristics (repetition rate, beam wavelength, pulse duration etc.) and to the material properties (optical, thermal, mechanical).
The possible combinations are fully capable to cover all needs and ideas but in the same time are limitless and sometimes chaotic. To address the aforementioned issue we have developed a theoretical framework to acquire fundamental understanding of laser-matter interaction and all the physical processes that occur after the irradiation of a solid surface with ultra-short laser pulses. In addition to this, this work is aiming to study systematically and provide capability to modulate thermal properties and surface modification of several materials.
The theoretical model presented in this thesis, combines the Two Temperature Model (originally proposed by Anisimov) to describe the energy absorption, the electron excitation, the electron-lattice heat exchange and relaxation processes, and the dynamic elasticity equations that characterize the elastic effects taking place at the surface of an irradiated material. The thesis is also enhanced by a mathematical analysis and a short introduction to Partial Differential Equations to help the reader repeat this work or study further.
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Interaction of ultra-short laser pulses with solid surfaces and double-layers
