Spectral and temporal characterization of nanosecond and femtosecond laser produced plasma from metallic targets

Experimental characterization and comparison of the temporal features of plasma produced by ultrafast (100 fs, 800 nm) and short-pulse (7ns, 1064 nm) laser pulses from a high purity nickel and zinc targets, expanding into a nitrogen background, are presented. The experiment is carried out under a wide pressure range of 10^-6 to 10^2 Torr, where the plume intensity is found to increase rapidly when the pressure approaches 1 Torr. Electron temperature (Te) is calculated from OES and is found to be independent of pressure for ultrafast excitation, whereas an enhancement in Te is observed around milliTorr regime for short-pulse excitation.The velocity measurements indicate acceleration of the fast species to a certain distance upon plume expansion, whereas the slow species are found to decelerate, particularly at higher pressures.A comparison of the time of flight dynamics of neutrals and ions in the LPPs generated by intense laser pulses confirms that the fast species observed are due to the recombination of fast ions with relatively slow moving electrons. Furthermore, an asynchronous pump-probe scheme is employed in the experiment that uses a Q-switched (1064 nm, 7ns) laser for plasma generation and the plasma thus generated is probed using a low power 100 fs, 82 MHz pulse train, which allows the probing of the transient LPP at every 12 ns intervals.