Ultra-high speed laser-surgery with ultrafast bursts of pulses

Ultrafast lasers allow thermal damage-free ablation irrespective of the material type. However, this process is slow and inefficient, with ablation volume having the remarkably poor logarithmic depedence on incident pulse energy. We recently demonstrated (Ilday et al., Nature 2016) ablation-cooled laser-material, whereby ultrafast pulses are sent in bursts, each containing hundreds of pulses separated by merely 100s of picoseconds, such that there is no time for heat to diffuse away from the processing region. The ablation rate increases by orders of magnitude and ablation becomes the dominant heat removal mechanism. Thus, the rest of the target material remains cool and without damage. We also reduced the required laser pulse energies by 1000 times and achieved record speeds in cutting biological tissue, metals and semiconductors (reaching 1 mm^3/s). This new regime, where the ablation volume scales linearly with burst energy, has received much industrial interest, but there is also remarkable potential for extremely high-efficient and fast laser surgery. Is it possible to reach 1 mm³/s with biological tissue without thermal damage? As a more basic question, what the limitations to further decreasing the pulse separation time to less than the time it takes for ablation to occur.