The use of femtosecond laser pulses allows precise and thermal-damage-free removal of material (ablation) with wide-ranging scientific1, 2, 3, 4, 5, medical6, 7, 8, 9, 10, 11 and industrial applications12. However, its potential is limited by the low speeds at which material can be removed1, 9, 10, 11, 13 and the complexity of the associated laser technology. The complexity of the laser design arises from the need to overcome the high pulse energy threshold for efficient ablation. However, the use of more powerful lasers to increase the ablation rate results in unwanted effects such as shielding, saturation and collateral damage from heat accumulation at higher laser powers6, 13, 14. Here we circumvent this limitation by exploiting ablation cooling, in analogy to a technique routinely used in aerospace engineering15, 16. We apply ultrafast successions (bursts) of laser pulses to ablate the target material before the residual heat deposited by previous pulses diffuses away from the processing region. Proof-of-principle experiments on various substrates demonstrate that extremely high repetition rates, which make ablation cooling possible, reduce the laser pulse energies needed for ablation and increase the efficiency of the removal process by an order of magnitude over previously used laser parameters17, 18. We also demonstrate the removal of brain tissue at two cubic millimetres per minute and dentine at three cubic millimetres per minute without any thermal damage to the bulk9, 11.
At a glance
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- Video 1: Animated version of the schematic description of ablation cooling in Figure 1 (288 KB, Download)
- The colouration is based on a mapping of temperature profiles as determined from simulations for the case of 800-MHz pulses (ablation cooling regime) and 10-MHz pulses (outside of the ablation cooling regime). The time and depth coordinates are normalized to characteristic values, as defined in the section below on numerical simulations. While the simulations are 1D, we have taken the liberty of assuming that the profile stays the same in drawing cross-sectional temperature profiles for simplicity. This approximation will not, however, change the main features of the result and the movie is intended to be an illustration, and not an accurate representation of the simulation results.
- Video 2: Shot during material processing experiments using 100-MHz intra-burst repetition rate pulses and 25-kHz uniform repetition rate results on a steel target with the same power. (6.39 MB, Download)
- The major difference in the sound and plasma brightness is indicative of and consistent with roughly order of magnitude increases in ablation rates in the ablation-cooling regime.
- Video 3: 3D representation of the laser-processed brain tissue (9.07 MB, Download)
- This video shows a 3D representation of the laser-processed brain tissue obtained through micro-CT imaging.
- Supplementary Information (16.3 MB)
This file contains Supplementary Text and Data, Supplementary Figures 1-47, Supplementary Tables 1-5, Supplementary Video legends and additional references (see Contents for more details).