Expansion and backscattering of laser produced Fe plasma plume

Forward and backward moving atoms within the laser produced plasma plume were studied by means of a cavity ringdown spectroscopy. The plume was produced using a nanosecond Nd-YAG laser pulse illuminating stainless steel target in a vacuum or helium background gas. Measurements were done at pressures ranging from 10− 5 to 1 mbar. Atomic absorption line shapes of iron around 388 nm were measured above and below the target at different times after the ablation initiation. Changes in absorption line shapes were used to estimate kinetic parameters of the plasma plume. The observations were interpreted through modeling which takes into account the angular and velocity distributions of atoms in the expanding plume. The amount of backward scattered atoms was about 10% of the total number of particles.

► Fe absorption line shapes in laser ablation using CRDS.
► Measurement at different distances from the target and different helium pressures.
► The expansion can be described using a simple model.
► Backscattering occurs at the beginning of cloud expansion just above the target.
► 10% of particles backscattered at 10− 5 mbar.