Contrast improvement of sub-4 fs laser pulses using nonlinear elliptical polarization rotation.

Temporal-intensity contrast is crucial in intense laser-matter interaction to circumvent the undesirable expansion of steep high-density plasma prior to the interaction with the main pulse. Nonlinear elliptical polarization rotation in an argon filled hollow-core fiber is used here for cleaning pedestals/satellite pulses of a chirped-pulse-amplifier based Ti:Sapphire laser. This source provides ∼35 µJ energy and sub-4-fs duration, and the process has >50% internal efficiency, more than the most commonly used pulse cleaning methods. Further, the contrast is improved by 3 orders of magnitude when measured after amplifying the pulses to 16 TW using non-collinear optical parametric chirped pulse amplification with a prospect to even further enhancement.

Plasma plumes produced by laser ablation of Al with single and double pulse schemes.

We generated and characterized plasma with single and double picosecond laser pulses to study the plume dynamics and to control the plasma properties. The double pulse scheme was found to be superior for generating a homogeneous plasma. Lateral expansion was prominent in irradiation schemes wherein the energy in the first pulse is lower than or equal to that of the second pulse. The velocities of the fast and slow species were found to be nearly equal with the emission counts corresponding to slow species being larger for the single pulse compared to the double pulse.