Industrial applications of ultrafast laser processing
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oduction Ultrafast lasers, which are pulsed lasers with pulse duration in the femtosecond (fs) or picosecond (ps) range, have gained wide acceptance over the past several years as a unique tool for advanced high-precision manufacturing. The ultrashort pulse duration and the high intensity on the target lead to complete ionization of the irradiated volume by nonlinear effects. Since the pulse duration is less than the heat diffusion time, the irradiated volume is ejected before any heat diffusion or thermal damage can take place, and consequently, side effects are significantly reduced as compared to longer pulses. The decreased side effects result in preserving the functionalities of the material and enable fine and accurate microfabrication processes such as drilling, cutting, engraving, and internal marking. However, because of the non-thermal nature of the ablation process, the quantity of matter removed per laser pulse is relatively small, and many technology developments have taken place to ensure that the overall industrial process reaches a productivity scale sufficient for economic use. In particular, three fields have been key to the current development of industrial laser applications: Laser technology, ultrafast laser– matter interactions, and beam handling and delivery.
The average power of the laser is key for high-throughput industrial use. The first generation of ultrafast lasers, introduced in the early 2000s, had an average power of 1 W. Today, multiple technologies allow average laser power levels to reach between 100 W for industrial lasers and more than 1 kW in scientific proofs-of-principle experiments.1–3 The key feature is the capacity of the laser medium to dissipate the heat generated while under high-average-power operation. Fiber lasers allow a high average power to be easily reached by distributing the heat along the fiber length. However, specific fiber geometries such as microstructured photonic crystal fibers are required to offer an energy per pulse sufficient for industrial applications.1 On the other hand, thin disk lasers (i.e., lasers using a thin laser crystal as the active material for efficient heat dissipation) can provide both high energy and high average power, but the laser repetition rate is usually limited to a few hundred kHz.2 Other approaches, such as the use of multipass slab geometries, also show significant potential.3 Today, industrial lasers with power in the range of 100 W are commercially available from several manufacturers, with most of them operating with moderate pulse energies (typically
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