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The interaction of ultrashort laser pulses with materials is the subject of much modern research due to their ability to reach terawatt peak powers. Novel methods for temporally structuring femtosecond pulses have led to a new regime of burst mode ablation. The combination of burst mode operation with laser filamentation has been used to generate stitched filaments which form long-lasting plasma channels and can lead to increased laser ablation upon material interaction. In this work, laser ablation theory is discussed and compares the ablation effects of single, smoothly varying nanosecond pulses to a nanosecond envelope containing a GHz burst of femtosecond pulses. To directly compare the ablation efficiency by bursts of femtosecond pulses, a high-power nanosecond laser is used to ablate silicon and aluminum samples with energies comparable to the envelope energies of a burst of 32 hundred-femtosecond pulses each separated by 400 ps, as well as a bursts of 16 pulses separated by 400 or 800 ps. This experiment showed clear superiority of femtosecond burst mode over traditional nanosecond pulses at ablation at high fluences, with efficiencies forty times higher in aluminum and fourteen times higher in silicon. For the first time ever, burst mode operation was outfitted on a filamentation laser for outdoor propagation, and ablation measurements were measured after 250 meters of propagation. Single femtosecond pulses were compared to bursts of 8 pulses separated by 400 ps, and ablation craters were found only for burst modes at the highest energy during periods of low turbulence. The lack of ablation under other conditions suggests that turbulence plays a pivotal role in burst mode ablation efficacy during outdoor propagation and gives cause for further experiments at a distance.

Laser filaments are beneficial in long range outdoor applications. An intense ultrashort pulse will propagate nonlinearly through air and experience a balance of self-focusing and defocusing effects to generate a filament consisting of a plasma channel and high-intensity light beam over a long range of propagation. Filaments can propagate several times the Rayleigh distance, allowing the projection of high energy densities in a small spot size over kilometer scale distances. However, filaments are limited by clamped values of their intensity, plasma electron density, plasma lifetime, and spot size. We have previously demonstrated the "stitching" of filaments to extend the plasma lifetime. This was accomplished via our burst mode optical pulse system (BMOPS), which produces a 13 ns burst of pulses separated by an interval shorter than the plasma lifetime at the 10 Hz laser repetition rate, resulting in a higher average power than a single pulse. Stitching temporally separates and precisely spatially overlaps pulses to produce a filament with a lifetime many times that of a filament formed by a single pulse. This enhanced lifetime can improve the performance of many filamentation applications. We have recently implemented BMOPS into MU-HELF, our mobile ultrafast laser sitting on a 1 km range. Here, we present initial results of stitching and spatial confinement of burst mode energy over a 250 m range through turbulent conditions.