Showing papers by "Arkadi Rosenfeld published in 2007"

Spatial distribution of refractive index variations induced in bulk fused silica by single ultrashort and short laser pulses

Abstract: We correlate phase-contrast microscopy of modification tracks induced by tightly focused single ultrashort and short laser pulses inside fused silica with numerical simulations of nonlinear laser excitation footprints. Different pulse durations on the femtosecond and picosecond range are compared in order to validate the experimental and theoretical observations on the subsequent refractive index variations in a regime where linear and nonlinear contributions play a comparable role. The nature of the laser-induced structural changes depends essentially on the characteristics of pulse propagation in different regions of the irradiated zone. Numerical simulations of laser pulse propagation in the excited region show that accumulation of excess energy and swift nonlinear absorption contribute to the formation of either positive or negative phase-shift regions within the same single-pulse-induced damage trace. The decrease in the refractive index can be unambiguously correlated with the regions of maximum energy deposition during prolonged exposure times.

Theoretical Models and Qualitative Interpretations of Fs Laser Material Processing

Abstract: In this paper a number of numerical models are presented which have been developed to describe the processes taking place at different time and length scales in different classes of materials under the irradiation by ultrashort laser pulses. A unified drift-diffusion approach for modeling charge- carrier transport in metals, semiconductors, and dielectrics allows to elucidate the dynamics of the electric field generated in the target due to photo-emission and to get insight into the origin of the Coulomb explosion process. The widely known two-temperature model is used to follow heating dynamics of irradiated matter and to analyze its phase transformations on the basis of thermodynamic concepts. Being modified for semiconductors, this model has allowed to establish the nature of high-energeti c ion emission using laser pulse tailoring and to undertake a simplified modeling of consequences of ultrafast melting of silicon. A two-dimensiona l model of dielectric breakdown has made possible to uncover the mechanisms which enable the spatial modulation of the structures induced by temporally modulated laser pulses in wide-band-gap dielectric materials. A combined thermal/elasto-plastic model has provided a deep insight into the mechanisms and dynamics of the microbump and nanojet formation on nanosize gold films under femtosecond laser irradiation.

Theoretical Models and Qualitative Interpretations of Fs Laser Material Processing

Abstract: In this paper a number of numerical models are presented which have been developed to describe the processes taking place at different time and length scales in different classes of materials under the irradiation by ultrashort laser pulses. A unified drift-diffusion approach for modeling chargecarrier transport in metals, semiconductors, and dielectrics allows to elucidate the dynamics of the electric field generated in the target due to photo-emission and to get insight into the origin of the Coulomb explosion process. The widely known two-temperature model is used to follow heating dynamics of irradiated matter and to analyze its phase transformations on the basis of thermodynamic concepts. Being modified for semiconductors, this model has allowed to establish the nature of high-energetic ion emission using laser pulse tailoring and to undertake a simplified modeling of consequences of ultrafast melting of silicon. A two-dimensional model of dielectric breakdown has made possible to uncover the mechanisms which enable the spatial modulation of the structures induced by temporally modulated laser pulses in wide-band-gap dielectric materials. A combined thermal/elasto-plastic model has provided a deep insight into the mechanisms and dynamics of the microbump and nanojet formation on nanosize gold films under femtosecond laser irradiation.

Modeling of electron dynamics in laser-irradiated solids: progress achieved through a continuum approach and future prospects

Abstract: A continuum model based on a drift-diffusion approach is applied to describe the dynamics of electronic excitation, heating and charge-carrier transport in metals and dielectrics under near-infrared femtosecond laser irradiation. The dependence of laser-induced charging of the targets on laser fluence and pulse duration is investigated. Various aspects concerning the mechanism of Coulomb Explosion (CE) are discussed. The CE threshold as a function of pulse duration is evaluated numerically for dielectric materials (sapphire and ULE glass). A special attention is paid to studies of interconnection between the electron emission yield and surface charging dynamics. It has been found that in dielectrics the photoemission yield saturates with increasing laser fluence as a result of self-regulation of the free-electron population. By contrast in metals, due to effective supply of electrons to the charging zone on the target surface, electron emission becomes unwarrantably high for short laser pulses and high fluences. However, photo- and thermionic emissions can be suppressed by the generated electric field whose amplitude is a function of pulse duration and laser fluence. The question on self-consistency of electron emission and surface charging is analyzed with outlining further studies.

Fast Electronic Transport and Coulomb Explosion in Materials Irradiated with Ultrashort Laser Pulses

Abstract: Nadezhda M. Bulgakova', Razvan Stoian^, Arkadi Rosenfeld^, Ingolf V. HerteP^ and Eleanor E.B. Campbell' 'Institute of Thermophysics SB RAS, I Lavrentyev Ave., 630090 Novosibirsk, Russia ^Laboratoire TSI (UMR 5516 CNRS), Universite Jean Monnet, 10 rue Barrouin, 42000 Saint Etienne, France, ^Max-Born-Institut fiir Nichtlineare Optik und Kurzzeitspektroskopie, MaxBorn Str. 2a, D-12489 Berlin, Germany, * Department of Physics, Free University of Berlin, Amimallee 14, 14195 Berlin, Germany, ^Department of Physics, Goteborg University, SE41296 Goteborg, Sweden