Research progress in ultrafast fiber lasers for material micromachining

Previously, we have continuously improved and innovated in technology by using fiber lasers. This paper reviews the research progress in material micromachining using high repetition rate fast fiber lasers in recent years. In the study of other materials, some new characteristics and functions of laser processed materials have been discovered, making ultrafast fiber lasers not only a powerful material shaping tool, but also a promising tool for efficient material preparation.

Pulsed laser deposition technology for preparing thin films has been widely used in basic research on new materials. High-power nanosecond pulsed laser ablation will cause plasma plume (feather-like luminous group) to produce a large number of molten droplets, which will affect the quality of the film. There are many mechanical and electronic methods to solve the molten drop problem by controlling the ablation plume. One alternative is high repetition rate ultrafast fiber lasers. The method is particularly suitable for collecting laser pulses into bursts, each containing several independent pulses, which can achieve more precise thermal control and directly vaporize the target without producing large droplets.

Fiber laser systems can output pulse trains directly from the laser source, that is, pulse sequences. For example, before amplification, an acousto-optic modulator can be used to screen a 50MHz oscillator and finally output a pulse train consisting of multiple pulses with a 20 nanosecond interval between consecutive pulses. The short pulse interval of 20 nanoseconds may produce multiple cumulative effects, including heating of the target, ablation plume, and heating between laser pulses, which ultimately optimizes the film quality. TiO2 thin films were prepared using this method. The film quality was very good as observed by transmission electron microscopy, with atomically smooth surfaces and a very smooth interface between the film and the substrate. No large droplets were observed by optical microscopy within 100 mm.

Recent studies have shown that laser-formed metal surfaces are highly hydrophobic (they do not contain water) under certain conditions. Laser-induced linear and particle-shaped scanning electron microscopy (SEM) prepared by linear and circular polarization. Water droplets are shown on the laser pattern of stainless steel surface. Its acute angle is less than 30掳, indicating that the metal surface is highly hydrophobic, which enables it to form a composite surface composed of porous solids and air encapsulated in air, thereby reducing contact with water.

If large-area, superhydrophobic metal surfaces can be processed using high-repetition-rate ultrashort-pulse lasers and robots, the technology could be used to manufacture large outdoor equipment, such as wind turbine blades with anti-icing surfaces. The search for an effective method is still ongoing, and the more successful photolithography methods are limited to research laboratories and are expensive.

This paper introduces a special pulsed laser deposition process, laser-induced back transfer (LIBT), which can be used for high-resolution laser direct writing. The technology uses a laser beam to pass through a transparent substrate to ablate a nearby target. The vapor is pressed into the transparent substrate by the laser, causing it to precipitate. LIBT technology is widely used in the laser field. Fiber laser technology enables large-scale, continuous grayscale image printing, which is only possible at high repetition rates in the MHz range. The computer-controlled beam scanner changes the scanning speed according to the grayscale level of the image. High repetition rate pulses will cause multiple pulses to overlap in space, and the corresponding deposition will also accumulate, presenting a continuous grayscale visual effect.

As far as the current technical situation is concerned, ultrafast fiber lasers are gradually becoming a powerful tool in micro-material processing.