The higher the power and the processing of high reflective materials, the faster the thermal expansion of optical elements, the more obvious the thermal lens; When the thermal lens effect is produced, the optical element is heated and expands, resulting in stronger focusing ability, smaller focusing spot size, shorter focal length and focal depth. These phenomena, will eventually cause laser processing instability, affect the laser processing effect. 1. Influence on marking (1) alumina black: thermal lens effect occurs, the focal length is shorter, the energy density of the material surface is reduced, alumina black, serious center and edge effect blackness inconsistent phenomenon. (2) metal deep carving: metal deep carving generally uses a field mirror with a short focal length (focal depth). When high power deep carving, due to the thermal lens effect, the energy density at the material decreases rapidly, resulting in the metal not deep. As the center of the optical element expands larger than the edge, it is shallow in the center and deep around (the depth is inconsistent). (3) thin slice cutting: according to different materials, pulse fiber laser cutting thin slice usually use a single slow speed or many times fast these two methods. Thermal expansion and cooling retraction can occur in a very short time (< 1S), so when cutting, the initial position can be cut through, and other positions can not cut through the material. 2. Influence on welding (1) Spot welding of metal sheet: for spot welding of metal sheet by high-power fiber laser, the thermal lens effect will cause inconsistent solder spot size, welding instability and insufficient drawing force. (2) metal continuous welding: continuous light welding metal relative to cutting, higher reflectivity. In the case of high power welding, the thermal lens effect will cause the normal part before welding, while the welding depth of the rear part is shallow or completely impenetrable. Welding aluminum and copper high - reflective materials, thermal lens effect is more obvious. 3, the impact of cutting (1) stainless steel cutting: stainless steel cutting, the thermal lens effect will cause the cutting surface is not consistent, hanging slag more and more, and even continuous cutting problems. (2) carbon steel cutting: carbon steel cutting, the thermal lens effect will cause more and more slag at the bottom, cutting continuous problems.