Cavity ringdown spectroscopy of collinear dual-pulse laser plasmas in vacuum

The plasma plume induced by dual-pulse laser ablation of a titanium target in vacuum was analyzed by the technique of cavity ringdown spectroscopy (CRDS). Large Doppler-splitting of the absorption spectral lines was observed which is due to increase of the velocity components parallel to the optical axis and specific features of the CRDS measurements. Vertical velocity component, the particle number density and plasma volume also show increase compared to the single-pulse laser ablation. The forward convolution best fit of absorption lineshapes was used to extract parameters describing dual-pulse laser ablation plasma plume.