Laser Classification

There are two main types of lasers used for welding, namely CO2 laser and Nd:YAG laser. Both CO2 laser and Nd:YAG laser are infrared light that is invisible to the naked eye. The beam generated by Nd:YAG laser is mainly near-infrared light with a wavelength of 1.06 lm. Thermal conductors have a high absorption rate for light of this wavelength. For most metals, its reflectivity is 20% to 30%. As long as a standard optical mirror is used, the near-infrared band beam can be focused to a diameter of 0.25 mm. The beam of CO2 laser is far-infrared light with a wavelength of 10.6 lm. Most metals have a reflectivity of 80% to 90% for this light. Special optical mirrors are required to focus the beam to a diameter of 0.75-0.1 mm. The power of Nd:YAG laser can generally reach about 4,000 to 6,000 W, and the maximum power has now reached 10,000 W. However, the power of CO2 laser can easily reach 20,000 W or even greater.
High-power CO2 lasers solve the problem of high reflectivity through the pinhole effect. When the surface of the material irradiated by the spot melts, a pinhole is formed. This small hole filled with steam is like a black body, absorbing almost all the energy of the incident light. The equilibrium temperature in the cavity reaches about 25,000 e. Within a few microseconds, the reflectivity drops rapidly. Although the development focus of CO2 lasers is still on the development and research of equipment, it is no longer on improving the maximum output power, but on how to improve the beam quality and its focusing performance. In addition, when CO2 lasers are welded at high power above 10 kW, if argon shielding gas is used, very strong plasma is often induced, which makes the melting depth shallower. Therefore, when CO2 lasers are welded at high power, helium, which does not produce plasma, is often used as a shielding gas.
The application of diode laser combinations for exciting high-power Nd: YAG crystals is an important development topic, which will greatly improve the quality of laser beams and form more effective laser processing. The laser with output wavelength in the near-infrared region is excited by direct diode array, and its average power has reached 1 kW, and the photoelectric conversion efficiency is close to 50%. The diode also has a longer service life (10,000 hours), which is conducive to reducing the maintenance cost of laser equipment. Development of diode-pumped solid-state laser equipment (DPSSL).