Modeling for Copper Ablation by Ultrashort Laser Bursts-Train

Ablation of copper using multipulse femtosecond laser irradiation with an 800 nm wavelength and 900-fs pulse duration is investigated theoretically using a dynamic tow temperature model. Our results show that the irradiation of a metal film by burst femtosecond laser with a separation time between pulses less than the thermal relaxation time can dramatically enhance the irradiated focal volume without a significant dissipation of the energy inside the material. We demonstrate the advantage of burst irradiation at low fluence where the cooper can be ablated below single ablation threshold. We also suggest that at high fluence, irradiation with a burst-train may give rise to a cleaner ablation than with a pulse-train

A simple thermodynamical witness showing universality of macroscopic entanglement

We show that if the ground state entanglement exceeds the total entropy of a given system, then this system is in an entangled state. This is a universal entanglement witness that applies to any physical system and yields a temperature below which we are certain to find some entanglement. Our witness is then applied to generic bosonic and fermionic many body systems to derive the corresponding "critical" temperatures that have a very broad validity.Comment: 3 pages, Torun conference, June 25-28, 200

Numerical investigations on high-power laser cutting of metals

A theoretical approach based on a numerical simulation using experimental data is proposed as a contribution for the study of laser metal cutting under gas assistance. The aim is to simulate the stages of the kerf formation by considering the induced generated melt film dynamics, while it interacts with the laser beam and the assisting gas jet. For normal atmospheric conditions, a 3D model is developed using the finite volume method to solve the governing hydrodynamic equations, supplied with the species conservation equation. The present air, the metallic liquid, and the solid metal are considered as phases, where the interface positions are tracked by implementation of the volume-of-fluid method through Fluent CFD code, whereas an enthalpic method is used to take into account the material melting and resolidification. The results for six operating conditions in relation to the cutting velocity show an interesting agreement with the experimental observations

How Plasmonic excitation influences the LIPSS formation on diamond during multipulse femtosecond laser irradiation ?

A generalized plasmonic model is proposed to calculate the nanostructure period induced by multipulse laser femtosecond on diamond at 800 nm wavelengths. We follow the evolution of LIPSS formation by changing diamond optical parameters in function of electron plasma excitation during laser irradiation. Our calculations shows that the ordered nanostructures can be observed only in the range of surface plasmon polariton excitation

The efficacy of plasmonic model to calculate HSFL nanostructure period in Sapphire

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How Plasmonic excitation influences the LIPSS formation on diamond during multipulse femtosecond laser irradiation ?

A generalized plasmonic model is proposed to calculate the nanostructure period induced by multipulse laser femtosecond on diamond at 800 nm wavelengths. We follow the evolution of LIPSS formation by changing diamond optical parameters in function of electron plasma excitation during laser irradiation. Our calculations shows that the ordered nanostructures can be observed only in the range of surface plasmon polariton excitation

Optical and Thermal Behavior of Germanium Thin Films under Femtosecond Laser Irradiation

In this study, we theoretically investigate the response of a germanium thin film under femtosecond pulsed laser irradiation. Electron and lattice temperatures, as well as material-specific optical properties such as dielectric function and reflectivity, were calculated during the irradiation using an extended two-temperature model coupled with the carrier density rate equation and the Drude model. Melting and ablation fluence thresholds were also predicted, resulting in 0.14 J cm−2 and 0.35 J cm−2, respectively. An ultrafast change in both optical and thermal properties was detected upon laser irradiation. Results also indicate that thermal melting occurs after germanium takes on a metallic character during irradiation, and that the impact ionization process may have a critical role in the laser-induced thermal effect. Therefore, we suggest that the origin of the thermal modification of germanium surface under femtosecond laser irradiation is mostly due the impact ionization process and that its effect becomes more important when increasing the laser fluence