Classical modelling of the nonlinear properties of clusters in strong low-frequency laser fields

Abstract

The nonlinear collective electron dynamics of a cluster irradiated by a strong near-infrared linearly polarized short laser pulse are studied by classical molecular-dynamics simulations for a small model cluster with ∼103 particles. The model naturally yields all the features of a cluster exposed to a strong laser pulse, such as inner and outer ionization, expansion of the ion core, etc. When the frequency of the incident radiation is near three-photon resonance with the Mie frequency in the laser-ionized cluster, both the electron acceleration and the local electric field acting on the ions inside the cluster exhibit a third harmonic of the fundamental frequency. The time evolution during the laser pulse of the third harmonic of the total electron acceleration as well as of the electric field inside the cluster is discussed for different parameters of the laser–cluster interaction. The effect of ion motion is investigated. The presence of a strong non-resonant second harmonic in the local electric field at ion positions off the cluster centre is reported.

Amplification of a high-frequency wave by IR-field-heatedclusters

“…This value is in quantitative agreement with the total width of the Mie resonance extracted from numerical simulations of the laser-cluster interaction in [55]. This comparison as well as physical arguments support the applicability of the results of the present letter at least within some domain of laser-cluster parameters.…”

Landau damping in thin films irradiated by a strong laser field

“…The latter may become particularly important, when it is nonlinearly excited. This was recently proposed theoretically [19,20] and observed experimentally [21] in laser-irradiated clusters. In references [17,19], the width of the Mie resonance was estimated assuming that the frequency of electron collisions with the boundary is…”

“…In contrast to the case of specular reflection when the general expression (11) for the rate of energy absorption is, in principle, a functional of the self-consistent potential, equation (20) cannot be solved in closed form for an arbitrary potential U (z) even in linear approximation with respect to the field (9) + . Therefore, the case of diffuse reflection can be considered analytically only for some particular selfconsistent potential.…”

“…(20) with the field (9) has the solution 6) where the subscript "+" indicates that the trajectory is calculated for an electron that starts its motion at the left side of the well at t = 0 (i.e. where the parameter x is the same as in (B.2).…”

Collisionless heating of a nanoplasma in laser-irradiated clusters

“…Moreover, nonlinear (three-photon) excitation of the Mie resonance in rare-gas clusters was theoretically studied [11][12][13] and observed in the experiment [14]. This was done for clusters of moderate size, for which the Mie frequency after inner ionization in a strong femtosecond pulse happens to be close to three times the frequency of the infrared laser field.…”