Possible surface plasmon polariton excitation under femtosecond laser irradiation of silicon

The mechanisms of ripple formation on silicon surface by femtosecond laser pulses are investigated. We demonstrate the transient evolution of the density of the excited free-carriers. As a result, the experimental conditions required for the excitation of surface plasmon polaritons are revealed. The periods of the resulting structures are then investigated as a function of laser parameters, such as the angle of incidence, laser fluence, and polarization. The obtained dependencies provide a way of better control over the properties of the periodic structures induced by femtosecond laser on the surface of a semiconductor material.Comment: 11 pages, 8 figures, accepted for publication in Journal of Applied Physic

Structure and Morphology Effects on the Optical Properties of Bimetallic Nanoparticle Films Laser Deposited on a Glass Substrate

Moving nanosecond laser system is used for laser-assisted thermodiffusion deposition of metallic nanoparticles from water-based colloidal solutions. The results obtained for both gold and silver nanoparticles show that film morphology strongly depends on laser scanning speed and the number of passages. We show, furthermore, the possibility of producing bimetallic Au:Ag thin films by laser irradiation of the mixed solutions. As a result of several laser scans, granular nanometric films are found to grow with a well-controlled composition, thickness, and morphology. By changing laser scanning parameters, film morphology can be varied from island structures to quasi-periodic arrays. The optical properties of the deposited structures are found to depend on the film composition, thickness, and mean separation between the particles. The transparency spectra of the deposited films are shown to be defined by their morphology

Invited Article: Filamentary deposition of laser energy in glasses with Bessel beams

We investigate the nonlinear absorption of laser energy in the bulk of transparent dielectrics for femtosecond and picosecond laser pulses focused by a conical lens. We highlight the influence of the pulse duration, laser pulse energy, and cone angle on laser energy absorption in transparent dielectrics. We provide a semi-analytical model allowing the calculation of maps for the density of nonlinear absorption of energy in BK7 and in SiO2 as a function of the pulse duration and peak fluence in the focal region. The comparison of the density of nonlinear absorption of energy with the available energy density determines optimal pulse durations and Bessel beam cone angles compatible with uniform laser energy deposition in the Bessel zone. The results reproduce quantitatively the transmission measurements for experiments in BK7 with picosecond pulses and suggest that the loss of propagation invariance and uniform laser energy deposition is responsible for a previously reported transition between different types of damage morphology in SiO2 [M. K. Bhuyan et al., Appl. Phys. Lett. 104, 021107 (2014)].We investigate the nonlinear absorption of laser energy in the bulk of transparent dielectrics for femtosecond and picosecond laser pulses focused by a conical lens. We highlight the influence of the pulse duration, laser pulse energy, and cone angle on laser energy absorption in transparent dielectrics. We provide a semi-analytical model allowing the calculation of maps for the density of nonlinear absorption of energy in BK7 and in SiO2 as a function of the pulse duration and peak fluence in the focal region. The comparison of the density of nonlinear absorption of energy with the available energy density determines optimal pulse durations and Bessel beam cone angles compatible with uniform laser energy deposition in the Bessel zone. The results reproduce quantitatively the transmission measurements for experiments in BK7 with picosecond pulses and suggest that the loss of propagation invariance and uniform laser energy deposition is responsible for a previously reported transition between different typ..

Transient optical response of ultrafast nonequilibrium excited metals: Effects of electron-electron contribution to collisional absorption

Approaching energy coupling in laser-irradiated metals, we point out the role of electron-electron collision as an efficient control factor for ultrafast optical absorption. The high degree of laser-induced electron-ion nonequilibrium drives a complex absorption pattern with consequences on the transient optical properties. Consequently, high electronic temperatures determine largely the collision frequency and establish a transition between absorptive regimes in solid and plasma phases. In particular, taking into account umklapp electron-electron collisions, we performed hydrodynamic simulations of the laser-matter interaction to calculate laser energy deposition during the electron-ion nonequilibrium stage and subsequent matter transformation phases. We observe strong correlations between optical and thermodynamic properties according to the experimental situations. A suitable connection between solid and plasma regimes is chosen in accordance with models that describe the behavior in extreme, asymptotic regimes. The proposed approach describes as well situations encountered in pump-probe types of experiments, where the state of matter is probed after initial excitation. Comparison with experimental measurements shows simulation results which are sufficiently accurate to interpret the observed material behavior. A numerical probe is proposed to analyze the transient optical properties of matter exposed to ultrashort pulsed laser irradiation at moderate and high intensities. Various thermodynamic states are assigned to the observed optical variation. Qualitative indications of the amount of energy coupled in the irradiated targets are obtained. Keywords: ultrafast absorption ; umklapp electron-electron collision ; collisional absorption ; laser-matter interactio

Nanofabrication with Pulsed Lasers

An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laser–matter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics

Numerical Analysis of Ultrashort Laser Ablation: Application for Fabrication of Nanoparticles and Nanostructures

International audienceIn this study, first we examine nanoparticle formation by femtosecond laser ablation under different experimental conditions. The dynamics of the laser plume expansion is investigated and the possibility of primary nanoparticle formation is analyzed. Then, we consider thermalization process in a background environment, diffusion-driven nucleation and longer scale nanoparticle aggregation/sintering. In addition, laser-assisted fragmentation of nanoparticles is examined, which can play a particular role in the multi-pulse regime. In this later case, nanoparticle size distribution results from an ensemble of processes thus revealing different particle populations. Calculations are performed for metals under different background conditions. The calculation results explain recent experimental findings and help to predict the role of the experimental parameters. The obtained nanoparticles are also used to form nanostructures. The performed analysis thus indicates ways of a control over the involved laser-assisted techniques

Laser-based synthesis of nanoparticles: role of laser parameters and background conditions

International audienceLaser ablation (LA) is a unique tool for nanoparticle synthesis. The main advantages of this method are in its green character and in the possibility of a control over particle size. In this study, we examine nanoparticle formation by laser ablation under different experimental conditions and analyse the results based on the developed models. The dynamics of the laser plume expansion is examined revealing the role of the background pressure and laser pulse parameters. As a result, the ablated material is compressed and a part of it becomes supersaturated. The so-called "primary" nanoparticles are formed at this stage. Then, nanoparticle aggregation/fragmentation enters into play leading to the formation of the secondary particles. In addition, laser- assisted fragmentation of nanoparticles is also examined. Based on numerical modeling we shed light on the above mechanisms by using different numerical approaches, such as molecular dynamics, Monte Carlo, numerical hydrodynamics, and analytical analysis. Calculations are performed for metallic targets under different background conditions. The obtained results explain recent experimental findings and help to predict the role of the experimental parameters. The performed analysis thus indicates ways of a control over nanoparticle synthesis © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Numerical study of the role of a background gas and system geometry in pulsed laser deposition

International audienceThe transport of laser ablated particles through a Maxwell-distributed ambient gas is simulated by Monte Carlo method. Three system geometry configurations frequently appearing in laser ablation experiments are considered: plume tilting, use of an interacting gas jet, and deposition on a substrate placed perpendicular to the laser-irradiated surface. The influence of the ambient gas on the formation of film thickness profiles and kinetic energy distributions of the deposited particles is studied. The thermalization of the laser plume and the backscattering of the ablated particles due to collisions with the background gas are investigated from two-dimensional film thickness distributions