Laser micromachining has attracted considerable interest because of its wide range of applications across nearly all manufacturing sectors and mostly in semiconductors such as silicon. However, modern micro-manufacturing demands progressive product miniaturization, high accuracy, and high-precision material removal. For this purpose, a fundamental study of the interaction between ultrashort laser pulses and silicon will be valuable for studying ablation characteristics and ablation performance. The femtosecond laser pulse interaction with the silicon is divided into five parts: 1) the interaction of laser light with the carriers, 2) variation of the carrier density and carrier temperature, 3) energy exchange between carriers and lattice, 4) thermomechanical response of the material, and 5) ablation. The evolution of the carrier density and carrier-lattice energy coupling equation is solved simultaneously to determine the optimum value of the ablation width and ablation depth of femtosecond laser pulses on the silicon. The first time, 2D axial symmetry thermal and non-thermal ablation profiles were compared with the experimental result at fluence ranging from 0.75 J/cm2to 9 J/cm2 at the wavelength of 515 nm and 180 fs laser on the silicon sample. A comparative study of damage thresholds from experiments and simulations is presented. The concordance between model calculations and experimental data demonstrates that fs laser ablation is thermal in nature in low fluence regime, whereas it is non- thermal in a high-fluence regime. Fundamental information such as the time evolution of the carrier density, carrier temperature evolution, and lattice temperature evolution can be obtained from the simulation results.

In this work, we performed an experimental investigation supported by a theoretical analysis of single-shot laser ablation of gold to study the laser-matter interaction for predicting the ablation morphology and optimizing the process parameters. A set of coupled partial differential equations of the two-temperature model with dynamic optical properties and a phase explosion mechanism were used to determine the temporal and spatial evolution of the electron and lattice temperatures. The primary research focus of this work is to use the GHz frequency to investigate the ablation performance because the irradiated material is still far from thermal equilibrium during the laser-matter interaction. In contrast to conventional single-pulse laser ablation, intra-burst frequencies and the number of pulses are important factors in optimizing ablation efficiency and quality for fast material processing. Theoretical investigation revealed that the ablation volume increased due to heat accumulation, but the ablation quality decreased as the intra-burst frequencies decreased from 1000 GHz to 10 GHz. Moreover, the specific ablation volume increases with a higher burst number and lower intra-burst frequency at the expense of ablation quality.

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