Interferometric Analysis of 1064-nm Nanosecond Laser Induced Copper Plasma

This paper reports on the interferometric analysis of laser-induced plasma performed to investigate the spatial and temporal dynamics of a plasma column as a function of the time elapsed after laser-induced ablation on the surface of a copper target. The plasma was driven by focusing Q-switched Nd:YAG laser pulse ( λ = 1064 nm, τ = ~ 5 ns, and E=12. 5 mJ) onto a copper target and the interference patterns were constructed using a Nomarski interferometer. Phase information of the interference patterns was extracted using a fast Fourier-transform method. With the phase information obtained thus the spatial distribution of electron density was inferred from the Abel inversion equation. For the infrared nanosecond pulsed ablation regime, we observed that the resulting plasma expands preferentially toward the incoming laser beam at the early stage of plasma formation. The maximum plasma density was measured to be of the order of ~ 10²⁰ cm^-3. As time elapses, the rapid radial expansion of plasma plume and significant reduction of electron density were observed.