Electronic mechanism of ion expulsion under UV nanosecond laser excitation of silicon: Experiment and modeling

We present experimental and modeling studies of UV nanosecond pulsed laser desorption and ablation of (111) bulk silicon. The results involve a new approach to the analysis of plume formation dynamics under high-energy photon irradiation of the semiconductor surface. Non-thermal, photo-induced desorption has been observed at low laser fluence, well below the melting threshold. Under ablation conditions, the non-thermal ions have also a high concentration. The origin of these ions is discussed on the basis of electronic excitation of Si surface states associated with the Coulomb explosion mechanism. We present a model describing dynamics of silicon target excitation, heating and harge-carrier transport

Environmentally Friendly Improvement of Plasmonic Nanostructure Functionality towards Magnetic Resonance Applications

Plasmonic nanostructures have attracted a broad research interest due to their application perspectives in various fields such as biosensing, catalysis, photovoltaics, and biomedicine. Their synthesis by pulsed laser ablation in pure water enables eliminating various side effects originating from chemical contamination. Another advantage of pulsed laser ablation in liquids (PLAL) is the possibility to controllably produce plasmonic nanoparticles (NPs) in combination with other plasmonic or magnetic materials, thus enhancing their functionality. However, the PLAL technique is still challenging in respect of merging metallic and semiconductor specific features in nanosized objects that could significantly broaden application areas of plasmonic nanostructures. In this work, we performed synthesis of hybrid AuSi NPs with novel modalities by ultrashort laser ablation of bulk gold in water containing silicon NPs. The Au/Si atomic ratio in the nanohybrids was finely varied from 0.5 to 3.5 when changing the initial Si NPs concentration in water from 70 µg/mL to 10 µg/mL, respectively, without requiring any complex chemical procedures. It has been found that the laser-fluence-insensitive silicon content depends on the mass of nanohybrids. A high concentration of paramagnetic defects (2.2·× 1018 spin/g) in polycrystalline plasmonic NPs has been achieved. Our findings can open further prospects for plasmonic nanostructures as contrast agents in optical and magnetic resonance imaging techniques, biosensing, and cancer theranostics

Fundamentals of ultrafast laser processing

When laser light of visible, near-IR or UV spectral range hits condensed matter, it interacts with the valance and/or conduction electrons of the system under action. Depending on laser intensity and irradiation geometry, the interaction can have different far-reaching consequences such as melting, ablation, changing of optical properties, mechanical and chemical transformations. Among existing laser systems, ultrafast lasers have become an extraordinary tool for processing of any kind of materials. With proper choosing the irradiation conditions, laser action allows either inducing highly-localized gentle modifications or obtaining strongly damaged material sites with desired or deleterious structures such as voids, periodic nanocracks, periodic surface structures or craters of various shapes and dimensions. This chapter presents a review on tremendous efforts of researchers in order to achieve clearer insights into laser-matter interactions in ultrashort irradiation regimes. The review does not pretend to completeness and aims to outline main ideas, achievements, and most intriguing findings still waiting for explanations and theoretical treatments

Laser-induced modification of transparent crystals and glasses

International audienceWe analyse theoretically the processes proceeding in transparent crystals and glasses irradiated by ultrashort laser pulses in the regimes typical of different applications in optoelectronics and photonics. We consider some phenomena, which have been previously described by the authors within the developed model representations: charge of the dielectric surface due to electron photoemission resulting in a Coulomb explosion; crater shaping by using an adaptive control of the laser pulse shape; optimisation of the waveguide writing in materials strongly resistant to laser-induced compaction under ordinary irradiation conditions. The developed models and analysis of the processes based on these models include the elements of the solid-state physics, plasma physics, thermodynamics, theory of elasticity and plasticity. Some important experimental observations which require explanations and adequate description are summarised

Theoretical treatments of ultrashort pulse laser processing of transparent materials: toward understanding the volume nanograting formation and "quill" writing effect

The dynamics of ultrashort-laser-induced generation of free electron plasma inside bulk glass is analyzed. The results of modeling are presented for typical glass modification regimes, obtained on the basis of Maxwell's equations supplemented with the equations describing electron plasma formation and the laser-induced electric current. The model has been demonstrated to allow revealing important features of laser beam propagation in the regimes of dense electron plasma generation such as strong scattering up to complete displacing of light from the plasma region followed by beam refocusing. The geometry of the laser energy absorption zone is determined, and the glass temperature is mapped which may be foreseen at the end of electron-glass matrix relaxation. This, in turn, allows estimating the laser-induced stress levels and making conclusions on the routes of glass modification. Finally, based on the modeling results, the plausible mechanisms are discussed which may be responsible for the formation of volume nanogratings in a number of transparent solids under the action ultrashort laser pulses and laser direct writing anisotropy observed for laser pulses with a tilted front

Highly regular nanostructuring of Si surface by ultrashort laser pulses

Sub-MHz repetition rate femtosecond laser pulses produce extremely regular periodic surface structures on silicon surface due to competition between ultrafast heating and electron-emission. They allow manufacturing of novel devices for solar, optoelectronic, and biomedical applications