The laser has the characteristics of good monochromaticity, coherence, directivity, and high brightness, and can be applied in many areas due to the pure light quality and stable spectrum. Lasers can be classified based on different working materials: solid lasers, gas lasers, liquid lasers, semiconductor lasers, and free electron lasers. Compared with traditional high-power CO₂ and YAG lasers, semiconductor lasers have obvious advantages, such as small size, lightweight, high efficiency, low energy consumption, long life, and high metal absorption of semiconductor lasers. With the continuous development of semiconductor laser technology, other solid lasers based on semiconductor lasers, such as fiber lasers, semiconductor-pumped solid lasers, and chip lasers, have also developed very rapidly.