Andrei P. Kanavin

Ablation of metals by ultrashort laser pulses: Theoretical modeling and computer simulations

Laser ablation of metals by femto- and picosecond pulses is analytically and numerically studied within the framework of different models for the ablated material. Within the plasma model ablation is initiated by high-power thermal and hydrodynamic waves which propagate into the irradiated material. Analytical expressions for the thermal ablation and for the ablation by the shock wave are obtained. Numerical simulations with the computer code RAPID are in a good agreement with analytical results.

Generation of acoustic oscillations by short laser pulses in metals

Nonlinear plasma effects important for femtosecond-scale heating dynamics are considered. It is shown that heating of electrons due to the inverse bremsstrahlung absorption of high-power short-pulse laser radiation results in parametric generation of ion-acoustic waves. The range of wave numbers where the amplitude of the ion-acoustic oscillations in-creases by more than an order of magnitude is determined. A self-similar description of electron and phonon kinetics in metals with a sharp gradient of the electron temperature is developed. It is shown that the Cherenkov generation of nonequilibrium phonons results in suppression of the electron heat flux and rapid disintegration of the metal lattice.

Thermal regime of laser ablation of metals by ultrashort pulses of low fluences

Thermal ablation of a metal surface by low-energy ultrashort laser pulses is considered theoretically. The temporal dynamics of the surface electron and lattice temperatures is studied within the framework of the two-temperature model and for different temperature dependencies of the characteristics of the metal (electron-relaxation time, heat capacity, thermal conductivity). The approximation of evaporation into a vacuum is used to determine the ablation depth. Analytical expressions for the ablation-threshold fluence Fth as well as the threshold values of the lattice temperature Tth(Fth) and the characteristic time of lattice temperature decay td(Fth) are obtained. This analytical description is in satisfactory agreement with particular numerical calculations.

Laser Nanostructurization of the Metal and Alloy Surfaces

The results from experimental and theoretical investigation of material pulsed laser treatment aimed at obtaining nano‐ and microstructured surface are presented. An experiment has been performed on the modification of indium surface using a solid‐state diode‐pumped laser. It has been shown that nano‐ and micro‐size structures are formed under laser melting and fast crystallization of the metal surface. The kinetics of the crystallization of metals under superfast cooling. The distribution function for crystalline nuclei dimensions is analytically found within the framework of the classical kinetic equation in case of superfast temperature changing. The average number of particles in the crystalline nuclei and relative volume of the crystalline phase are determined as functions of thermodynamic and laser treatment regime parameters. Good agreement is observed with experimental results for ultrashort laser pulses induced micro‐ and nanostructures production.

Amplification of acoustic oscillations by short laser pulses due to fast heating of electrons

It is shown that heating of electrons due to the inverse bremsstrahlung absorption of high-power short-pulse laser radiation results in parametric generation of ion-acoustic waves. The range of wave numbers where the amplitude of the ion-acoustic oscillations increases by more than an order of magnitude is determined.

Heat transport in metals irradiated by ultrashort laser pulses

Different regimes of heat propagation in metals irradiated by subpicosecond laser pulses are studied on the basis of two-temperature diffusion model. New analytical solutions for the heat conduction equation, corresponding to the different temperature dependences of the electron thermal conductivity (formula available n paper), are found. It is shown that in case of a strong electron-lattice nonequilibrium, the heat penetration depth grows linearly with time, lT varies direct as t, in opposite to the ordinary diffusionlike behavior, lT varies direct as t1/2. Moreover, the heat propagation velocity decreases with increasing laser fluence.

Acoustic waves in metals irradiated by ultrashort laser pulses

The generation of ion-acoustic waves in metals irradiated by ultrashort laser pulses is studied. It is shown that non- equilibrium ion-acoustic oscillations lead to an anomalous increase of the effective electron collision frequency and fast melting of metals.

High-power ultrashort pulse propagation in Raman-active media

The propagation of an intense femtosecond pulse in a Raman-active medium is analyzed. An analytic solution which describes in explicit form the evolution of the light pulse is derived. The field of an intense light wave undergoes a substantial transformation as the wave propagates through the medium. The nature of this transformation can change over time scales comparable to the period of the optical oscillations. As a result, the pulse of sufficiently high energy divides into stretched and compressed domains where the field decreases and increases respectively.

High-order harmonic generation in Raman-active media in strong laser fields

A novel mechanism for efficient high harmonics generation is proposed based on the self- scattering of powerful femtosecond light pulse in the Raman-active medium. Within the framework of the closed self-consistent model the pulse field electrodynamics are investigated, a simple analytical formula for the spectrum generated is derived. The plateau effect and the sharp cutoff of harmonic spectrum are predicted. Unlike the case of rare gases, the spectrum generated is found to be tuned by the variation of input ultrashort pulse intensity.