Ablation cooled material removal with bursts of ultrafast pulses

Abstract

Material processing with femto-second pulses allows precise and non-thermal material removal and being widely used in scientific, medical and industrial applications. However, due to low ablation speed at which material can be removed and the complexity of the associated laser technology, where the complexity arises from the need to overcome the high laser induced optical breakdown threshold for e cient ablation, its potential is limited. Physics of the interaction regime hinders a straightforward scaling up of the removal rate by using more powerful lasers due to e ects such as plasma shielding, saturation or collateral damage due to heat accumulation. In analogy to a technique routinely used for atmospheric re-entry of space shuttles since 1950s, ablation cooling, is exploited here to circumvent this limitation, where rapid successions of pulses repeated at ultrahigh repetition rates were applied from custom developed lasers to ablate the target material before the residual heat deposited by previous pulses di use away from the interaction region. This constitutes a new, physically unrecognized and even unexplored regime of laser- material interactions, where heat removal due to ablation is comparable to heat conduction. Proof-of-principle experiments were conducted on a broad range of targets including copper, silicon, thermoelectric couplers, PZT ceramic, agar gel, soft tissue and hard tissue, where they demonstrate reduction of required pulse energies by three orders of magnitude, while simultaneously increasing the ablation e ciency by an order of magnitude and thermal- damage-free removal of brain tissue at 2 mm3/min and tooth at 3 mm3/min, an order-of-magnitude faster than previous results.