Experimental research on thermal‐dynamic damage effect of K9 optical lens irradiated by femtosecond laser

Abstract The photothermal effect and photodynamic effect are the main factors causing the damage of materials when laser irradiates on it. Therefore, the damage effect of laser irradiation on optical lens evaluated by thermal and mechanical effects will contribute to the development of laser processing and laser damage. In order to study the damage effect of femtosecond laser irradiating on typical K9 optical lens, real‐time temperature during irradiation was measured by infrared thermal imaging combined with laser loading system, at the same time, high‐speed camera observed the irradiation process. Then, with the help of known parameters, the stress at the moment of laser loading was calculated. Finally, the optical lens target was placed under a scanning electron microscope for observation. The results show that maximum temperature and peak stress in experiments were lower than the damage threshold of optical lenses. With the increase of pulse repetition rate, the thermal damage has a cumulative effect, while the photo‐induced pressure only increases slightly. It leads to the dominance of mechanical damage in low‐frequency pulse irradiation, whereas in high‐frequency pulse irradiation, the opposite rule occurs. For transparent materials, the laser pulse shows a stronger damage effect, the product spatters in the direction opposite to the incident beam, while the plasma discharge damage product spatters in the opposite direction, so the damage occurs on both front and back surfaces of the material at the same time.