  Femtosecond pulses hold great promise for high-precision tissue removal.
However, ablation rates are severely limited by the need to keep average laser
power low to avoid collateral damage due to heat accumulation. Furthermore,
previously reported pulse energies preclude delivery in flexible fibers,
hindering in vivo operation. Both of these problems can be addressed through
use of groups of high-repetition-rate pulses, or bursts. Here, we report a
novel fiber laser and demonstrate ultrafast burst-mode ablation of brain tissue
at rates approaching 1 mm$^3$/min, an order of magnitude improvement over
previous reports. Burst mode operation is shown to be superior in terms of
energy required and avoidance of thermal effects, compared to uniform
repetition rates. These results can pave the way to in vivo operation at
medically relevant speeds, delivered via flexible fibers to surgically
hard-to-reach targets, or with simultaneous magnetic resonance imaging.
