The laser is regarded as one of the greatest inventions of the 20th century. With the end of the three industrial revolutions, the laser will be the key to lead the fourth industrial revolution. The appearance of laser greatly promoted the development of industry. Laser has become one of the most advanced and widely used means in machining because of its high power, easy focusing, high brightness and good directivity. Laser machining has high precision, high speed and low cost, which can be automatically controlled by computer programming. It can process complex structures without contact processing, which will not damage materials and is safe and reliable.
According to the mechanism of laser and material interaction, laser machining can be divided into two categories: laser thermal machining and non-thermal machining. The types of lasers commonly used in hot and non-hot machining are different. Hot machining usually USES long pulse laser or continuous lasaer pointer, while non-hot machining usually USES ultra-short pulse laser such as picosecond and femtosecond.
Laser thermal processing USES the thermal effect generated in the process of laser irradiation on materials. The molecular system of the irradiated material needs to constantly obtain energy from the irradiation laser and convert it into its own internal energy. The temperature in the irradiated area rises sharply to reach the melting and boiling point of the material, and then melts and removes it to achieve the processing purpose. Because it takes a long time for laser energy to be converted into internal energy of molecular system, long pulse laser is commonly used in thermal processing. This processing method is simple and direct, and has been widely used in industrial manufacturing, such as laser cutting and laser additive manufacturing. However, the accuracy and roughness of laser thermal processing are limited by the inevitable thermal diffusion.
Nonthermal is using the nonlinear effect of the disturbance caused by material electronic system, such as nonlinear ionization, surface scattering and so on), through the electronic absorption of photons transition and ionization, inducing material physical and chemical properties change, leading to some novel effect produced (such as laser two-photon polymerization, self-assembly, etc.), use of these novel effect as to enhance the machining precision, optimization method. Because the energy exchange between the electronic system and the laser can be completed in an instant, ultrashort pulses are commonly used in non-thermal processing. This kind of machining method has high precision and various machining means, which is one of the research hotspots in laser machining field.
With the continuous development of the industry, the traditional femtosecond laser processing technology cannot meet the increasing industrial demand, so it must be developed and optimized. Ultraviolet femtosecond laser machining technology is an effective way to improve machining accuracy and has great application value in industrial manufacturing. Femtosecond laser machining technology of vector and vortex light field changes the traditional single machining mode and makes laser machining more flexible and diverse. In addition, ultraviolet vector and vortex femtosecond laser processing technologies are also the practice and verification of the theory of interaction between light and matter, which is helpful to reveal the deeper physical mechanism and has positive scientific significance.