Dynamic stabilization and parametric excitation of instabilities in an ablation front by a temporally modulated laser pulse.

Abstract

We conducted a numerical study of the effects of the modulation amplitude and period of a temporally modulated laser pulse on instabilities at an ablation front. The physical features of the oscillatory acceleration and ablation velocity in unperturbed ablative flows display periodic oscillations. As the modulation amplitude or period is increased, the asymmetry of the oscillatory acceleration and ablation velocity becomes more evident, and the peak values of these quantities increase. The numerical solution of the Mathieu equation [R. Betti et al., Phys. Rev. Lett. 71, 3131 (1993)10.1103/PhysRevLett.71.3131] with a fitted acceleration was used to evaluate the behaviors of the oscillatory acceleration. The spatial structure and interfacial evolution of a single-mode ablative Rayleigh-Taylor instability (ARTI) were analyzed for the modulated laser pulses with different modulation amplitudes and periods. It was also observed in a previous work [K. G. Zhao et al., Phys. Rev. E 109, 025213 (2024)10.1103/PhysRevE.109.025213] that the modulated laser exerts a stabilizing influence on the growth of the ARTI in the intermediate- and long-wavelength regions. We found that increasing either the modulation amplitude or period enhances the dynamic stabilization of the ARTI while simultaneously inducing a characteristic destabilization of the parametric instability, which may excite the short-wavelength perturbations through the parametric resonance [G. H. Wolf, Phys. Rev. Lett. 24, 444 (1970)10.1103/PhysRevLett.24.444].