On the highly directional expansion of laser-produced plasmas

The expansion of plasmas produced by focusing a CO 2 laser pulse onto solid planar targets is discussed. The plasmas are studied using an extreme ultraviolet spectroheliograph. With titanium and iron targets the plasma blow-off observed in transitions within highly ionised species (e.g. Fe XVI) occurs parallel to the target normal. The plasma is tightly confined to narrow cylindrical structures about 0.7 mm in diameter, and is observed as far as 1 cm from the target surface. The electron density is about 2.8*10 18 cm -3 at a distance of 0.7 mm from the target surface and decreases to approximately 6.5*10 17 cm -3 at a distance of 2.9 mm from the surface.