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Ultra-short pulse lasers – materials - applications
1 , 1 , 1 , 1 , 1 , * 2
1  Swinburne University of Technology, Melbourne, Australia
2  Swinburne University of Technology
Academic Editor: Melon Zhang


From 2000, the average laser power of ultra-short (sub-1 ps) pulsed lasers has increased as Power = 2N/2 with N – number of the years from beginning of the trend, which parallels Moore’s law for number of transistors in an integrated circuit. Initially based on the chirped pulse amplification (CPA), which was awarded the Nobel prize in 2018, more recent approaches exploit different cavity geometries as well as amplification via the divided pulse and coherent beam combination. These strategies further increase the extracted power from solid state and fiber laser systems and makes them more compact. Ultra-short lasers with powers in the sub-1 kW range, ~1 mJ pulse energies and at the repetition rates up to ~1 MHz have become available. New modes of laser operation brings the capability to combine ultra-short pulses into MHz-GHz bursts with a controlled number of pulses per burst. It was shown that this burst mode of operation delivers ablation rates for metal and dental tissue on the order of 3 mm3/min. This is the rate that reaches that of current Electrical Discharge Machining/Grinding (EDM/G) CNC tools. This parity between material removal rate by discharge spark and laser beam was achieved in 2016. The burst mode advantage is in the possibility to fine tune material removal to the most efficient fluence [J/cm2], which is empirically determined to be e2= 7.4 times larger than the ablation threshold for the given material. Fine tuning to the optimum ablation rate is achieved by changing pulse number per irradiation spot, using beam scanning, and control of number of pulses per burst. For comparison of different fabrication conditions, the volume [mm3] ablated per 1 W average power per time 1 min: Va ~ mm3/W/min ~ mm3/(W.s) ~ mm3/J is used. This is the ablated volume-per-energy delivered by laser for subtractive machining (3D(-) printing). Interestingly, we show here that the volumetric energy density Energy/Volume ~ J/mm3 is the right measure for the additive mode of 3D(+) printing by ultra-short laser pulses. It is not surprising that accounting for the energy deposition in the volume of light-matter interaction is the essential measure for the both additive and subtractive 3D(+) and 3D(-) modes of 3D fabrication.

High average power ~sub-kW systems are targeting industrial applications. To handle high laser power, new beam delivery systems are developed for distribution of energy in a very well controlled and precise way over the workpiece. Photonic crystal fibers (holy-fibers), flexible delivery units, and polygon scanners with beam travel rates up to 1 km/s are readily available. These further contribute to compactness, versatility, and safety of high-power handling. This is especially important for open space and field deployable applications, e.g., surface texturing by ablation ripples for creation hydrophobic, anti-icing, and biocidal surfaces. These applications are particularly suitable for fast beam scanning techniques.

Here we overview recent development of 3D(+/-) printing from development of lasers, beam delivery tools, applications and materials. New polymerizable mixtures of colloidal particles, standard photo-polymerisable resists/resins can be tailored for required material composition. Calcination of the polymerised composites can be transferred into a glass, polycrystalline or ceramic state with feature sizes down to nanoscale.

Keywords: 3D printing, ablation, light matter interaction, femtosecond lasers, nanoscale