Ultra-fast pulsed digital holographic diagnosis of ejected material in femtosecond laser ablation of aluminum

The dynamic process of material ejection and plasma evolution in single 50 fs laser pulse ablation of aluminum target is investigated using pulsed digital micro-holography， and highly temporally and spatially resolved dynamic digital holograms are obtained. The secondary material ejection induced by the thermoelastic wave is observed in the holograms， and at the same time， we firstly report the phenomenon of anomalous fringe shift at large time delays that results from the effect of the ejected material towards the probe beam of 400 nm wavelength. Through digital reconstruction， the two-dimensional phase shift distribution of the probe beam is obtained. By employing inverse Abel transform， we also obtained the dynamic process of spatial and temporal evolution of refractive index and free electron density distribution of the plasma. The structure and composition of the ejected material is analyzed according to its optical properties which are obtained through experiment and calculation.