Ultrafast diagnostics of augmented filament ablation

High intensity ultrafast near-IR laser induced filaments in air possess very precise characteristics. Each filament is controlled in spatial extent by the non-linear optical processes that are responsible for their formation. The spatial extent of the filament has a Townesian profile comprising a central high intensity region of similar to 400 mu m full width, surrounded by a lower intensity peripheral field extending out several millimeters that maintains the long term propagation stability of the filament. The energy content within each filament is clamped by the threshold power needed for its establishment, for similar to 100 fs pulses this is similar to 3GW. Energy greater than this results in either the formation of additional filaments or is dispersed into the peripheral field and is diffracted out of the beam. Thus each filament carries a finite energy. Nonetheless, light filaments are an effective way of propagating over large distances extremely high power densities (> 10(13) W/cm(2)), several orders of magnitude higher than the ablation threshold of nearly all materials. The level of ablation of solid surfaces is however limited by the maximum energy (few mJ) carried in each filament. In the present study we make detailed measurements of the ablation of GaAs, examining both the plasma interaction and the resulting material ablation. In addition we probe the use of additional nanosecond infrared laser light focused on the surface concurrently with the filament at intensities. We observe significantly increased filament initiated ablation when followed by lower intensity nanosecond radiation. Ultrafast radiometric studies of the plasma evolution provides new understandings of this augmented ablation process.