Views: 34 Author: Site Editor Publish Time: 10-18-2021 Origin: Site
The thermal lens effect occasionally occurs in high-power fiber laser applications. For fiber laser marking machines, the laser output from the isolator head of the laser will be deflected by the galvanometer and focused by the field lens to mark the material at the focal point. . Therefore, the thermal lens effect is mainly produced on the galvanometer and field lens. So, how to solve the thermal lens effect in fiber laser marking? The Leapion laser analysis is as follows:
Due to the poor quality of optical components, dirt, damage and other reasons, the absorption rate of the laser is increased. After the optical components are irradiated by the laser beam for a long time, the temperature rises and thermal deformation occurs, which in turn causes the refractive index and the refractive index of the transmissive optical components. The reflection direction of the reflective optical element changes. The thermal lens effect will change the position of the laser focus (beam waist), thereby affecting the application effect.
Since the transmissive optical element has a higher absorption rate of laser light and a greater temperature rise, the thermal lens effect is more obvious.
When the quality of the field lens is not good and the thermal lens effect occurs, the focal length becomes shorter, the energy is not enough for marking under the original parameters, the marking is not black, the center and edge effects are inconsistent, and the focus needs to be re-adjusted.
Metal deep carving generally uses a field lens with a short focal length (focus depth). When high-power deep carving, due to the thermal lens effect, the energy density at the material drops rapidly, resulting in insufficient metal carving. Since the center of the optical element expands more than the edge, the center is shallow and the surrounding is deep (the depth is not consistent).
According to different materials, pulsed fiber laser cutting thin slices usually adopts two methods of single slow speed or multiple fast speeds. Thermal expansion and cooling retraction can occur in a short time (<1S), so the starting position can be cut through when cutting, and the material cannot be cut through other positions.
The galvanometer is mainly composed of a drive board, a servo motor and an X-Y optical reflection lens. When the reflectivity of the reflective lens is low, there are impurities in the medium, and the surface is contaminated, the lens will be thermally deformed when irradiated by the laser beam, and the flat mirror will become a convex mirror. After the laser beam passes through the two reflective lenses, the output spot will change. Larger, the focal spot becomes smaller and the focal depth becomes shorter after passing through the field lens.
The field mirror plays a role in focusing the output light spot in the fiber laser marking equipment, and its characteristic is that all the focal points are on a horizontal plane. The field lens is mainly composed of concave and convex lenses. When the transmittance of the lens group is low, there are impurities in the medium, and the surface is contaminated, the lens will be thermally deformed when irradiated by the laser beam, and the focusing ability of the lens will become stronger. And the depth of focus becomes shorter. The focus is not on a horizontal plane, and the marking effect of the center and the edge is inconsistent.
The thermal lens effect will have an impact on the stability of fiber laser marking, especially for the marking of sensitive materials.
1. Choose good quality galvanometer and field lens;
2. Perform routine maintenance on the galvanometer and field lens to prevent contamination of the lens by impurities;
3. Replace the damaged galvanometer and field lens;
4. Center the marking graphics, try to make the laser mark directly below the field lens;
5. Mark the material with curved surface so that the focus is a little bit lower than the top of the curved surface;
6. Clean the protective lens of the laser output head regularly to avoid contamination by impurities;
7. When using medium and high power (≥100W) pulsed fiber lasers, it is recommended to use composite materials or quartz materials for the field lens.
For more information and professional questions about more fiber laser marking machines, please contact Leapion Laser.
