Dynamical resonance shift and unification of resonances in short-pulse laser cluster interaction

Pronounced maximum absorption of laser light irradiating a rare-gas or metal cluster is widely expected during the linear resonance (LR) when Mie-plasma wavelength λ_M of electrons equals the laser wavelength λ. On the contrary, by performing molecular dynamics (MD) simulations of an argon cluster irradiated by short 5-fs (fwhm) laser pulses it is revealed that, for a given laser pulse energy and a cluster, at each peak intensity there exists a λ - shifted from the expected λ_M -  that corresponds to a unified dynamical LR at which evolution of the cluster happens through very efficient unification of possible resonances in various stages, including (i) the LR in the initial time of plasma creation, (ii) the LR in the Coulomb expanding phase and (iii) anharmonic resonance in the marginally over-dense regime for a relatively longer pulse duration, leading to maximum laser absorption accompanied by maximum outer ionisation and also maximum allowed average charge states. Increasing the laser intensity, the absorption maximum is found to shift in the band of λ ≈ (1-1.5)λ_M than permanently staying at the expected λ_M. Present study is important in future generation optimum control experiments where maximum energy is required to transfer from laser fields to charge particles.