Investigating plasma dynamics in mid-IR laser interactions with thin liquid sheets in air

Laser-plasma interactions with liquid targets have attracted significant attention for their role in high-energy density physics and plasma diagnostics. We present an investigation of plasma dynamics in mid-infrared (mid-IR) laser interactions with thin liquid sheet targets in air utilizing spatio-temporal microscopy. The experiment was performed at the iFAST facility and utilized a 2.5 µm, 44 fs laser operated at 1 kHz. A peak intensity of ~5.8 x 10¹⁶ W/cm² was achieved by focusing the laser with a pulse energy of 2 mJ on target to a spot size of 6.9 µm by 8.4 µm. Two types of liquids, distilled water and a 1 M CsCl aqueous solution, were investigated at multiple target thicknesses ranging from 2 µm to 6 µm, to captured plasma expansion dynamics up to 3.2 ns timescales.

The data reveals a subtle difference in plasma propagation between them, most notably, the plasma density for the CsCl solution appears to be slightly higher than that of the distilled water. These observations suggest that the presence of dissolved salts influences the plasma mechanisms, potentially due to enhanced conductivity, modified ionization dynamics, or differences in hydrodynamic evolution.