Transition from Surface to Volume Expansion in Argon Clusters Coulomb Explosion.

Area of Science:

• Plasma Physics
• Atomic and Molecular Physics
• Laser-Matter Interactions

Background:

• Understanding the dynamics of Coulomb explosions in small clusters is crucial for controlling nanoplasma evolution.
• Laser intensity significantly influences the ionization and expansion mechanisms of atomic clusters.

Purpose of the Study:

• To investigate the influence of laser intensity on the charge-state resolved ion energy spectra during the Coulomb explosion of small argon clusters.
• To identify the critical laser intensity threshold that governs the transition between different expansion regimes.

Main Methods:

• Utilizing the intensity-difference spectrum technique to record detailed ion energy spectra.
• Precisely controlling experimental parameters, including laser intensity and fluence.
• Simultaneously characterizing ion charge state and kinetic energy.

Main Results:

• A distinct change in nanoplasma expansion patterns was observed beyond a specific laser intensity threshold.
• Reduced laser intensity led to the appearance of low-energy 'cuts' in ion yields, absent at higher intensities.
• At low plasma electron temperatures, ionization saturation and surface effects favored surface-driven expansion.

Conclusions:

• The study reveals a transition from surface-driven to volume-driven Coulomb explosion with increasing laser intensity.
• Ionization saturation, recombination, and ion screening play critical roles in dictating the expansion dynamics.
• Precise control over laser parameters allows for manipulation of nanoplasma expansion characteristics.