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Measurements to control the morphology and characteristics of a picosecond laser produced chromium plasma plume upon double-pulse (DP) irradiation are presented and compared to their single-pulse (SP) counterpart. DP schemes are implemented by employing two geometries where the inter-pulse delay and the spatial separation are the control parameters. The ratio of plume length to plume width decreases upon increasing the inter-pulse delay and/or the energy of the second pulse in the collinear DP scheme. Interestingly, plasmas generated in the DP scheme at lower pressures resemble the expansion features of the plasma generated in the SP scheme at higher pressures. We find that DP schemes are advantageous for applications such as high harmonic generation and the production of quality thin films.

We have investigated nuclear dynamics in bound and dissociating acetylene molecular ions in a time-resolved reaction microscopy experiment with a pair of few-cycle pulses. Vibrating bound acetylene cations or dissociating dications are produced by the first pulse. The second pulse probes the nuclear dynamics by ionization to higher charge states and Coulomb explosion of the molecule. For the bound cations, we observed vibrations in acetylene (HCCH) and its isomer vinylidene (CCHH) along the CC-bond with a periodicity of around 26 fs. For dissociating dication molecules, a clear indication of enhanced ionization is found to occur along the CH- and CC-bonds after 10 fs to 40 fs. The time-dependent ionization processes are simulated using semi-classical on-the-fly dynamics revealing the underling mechanisms.

Laser produced plasmas are transient in nature, and their properties, which depend on the laser parameters as well as the material properties and the irradiation conditions, can be tailored for different applications. Highly ionized Al plasmas generated using 7 ns and negatively chirped 60 ps pulses are optimized for the purpose of generating Al IV and Al III, respectively. The plasma is optimized spatio-temporally for Al IV or Al III with irradiation energy as the control parameter using time-resolved optical emission spectroscopy. Plasmas attuned for higher charged states could be utilized as a good alternative source for the generation of high order harmonics.