Plasma Formation Dynamics in Intense Laser-Droplet Interaction

Abstract

We study the ionization dynamics in intense laser-droplet interaction using three-dimensional, relativistic particle-in-cell simulations. Of particular interest is the laser intensity and frequency regime for which initially transparent, wavelength-sized targets are not homogeneously ionized. Instead, the charge distribution changes both in space and in time on a sub-cycle scale. One may call this the extreme nonlinear Mie-optics regime. We find that - despite the fact that the plasma created at the droplet surface is overdense - oscillating electric fields may penetrate into the droplet under a certain angle, ionize, and propagate in the just generated plasma. This effect can be attributed to the local field enhancements at the droplet surface predicted by standard Mie theory. The penetration of the fields into the droplet leads to the formation of a highly inhomogeneous charge density distribution in the droplet interior, concentrated mostly in the polarization plane. We present a self-similar, exponential fit of the fractional ionization degree which depends only on a dimensionless combination of electric field amplitude, droplet radius, and plasma frequency with only a weak dependence on the laser frequency in the overdense regime.

5 pages, 6 figures

References in corpus (3)

• Laser-driven nonlinear cluster dynamics
• Laser-driven nanoplasmas in doped helium droplets: Local ignition and anisotropic expansion
• Steplike intensity threshold behavior of extreme ionization in laser-driven Xe clusters

Cited by in corpus (7)

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• The interaction of intense femtosecond laser pulses with argon microdroplets studied near the soft x-ray emission threshold
• The interaction of intense ultrashort laser pulses with cryogenic He jets
• Ionization dynamics of submicron-sized clusters in intense ultrafast laser pulses
• Anisotropic field ionization in nano-clusters mediated by Brunel-electron driven plasma waves
• Bright single-cycle terahertz source based on gas cells irradiated by two-color laser pulses
• High-order Mie resonance and transient field enhancement in laser-driven plasma nanoshells