Damage Mechanism Of Long-pulse Laser Induced Dielectric Films With The Threshold Measurements

The damage mechanisms and characteristics of dielectric films under the irradiation of the long pulse laser are studied in this paper. And damage threshold generated by long pulse laser with the wavelength of 1064nm is tested.MSP-1 type YAG long-pulse laser system with pulse width of millisecond scale is applied to build the dielectric film testing system in accordance with the international standards of ISO11254. This system can select a different combination of energy storage capacitors to control initial output energy of the laser, or through a series of attenuators to decay the laser energy. Energy density is further adjusted by changing the size of spot. And the occurrence of film damage is judged by combining the methods of the plasma spark and phase contrast microscopy observation.The testing method of 1-on-1 based on the international standards is used to measure damage threshold (LIDT) of ZrO₂/SiO₂ high-reflection film induced by laser. And then the reasons why the HR films have a high damage threshold against laser are analyzed. Because of the high melting point and the high intensity of ZrO₂/SiO₂ high-reflection film and the SiO₂ film as a protective film, the ability of dielectric film to resist laser damage is improved.In this experiment, the LIDT of Al₂O₃/SiO₂ anti-reflection film is tested. According to the experiment, the phenomenon is found that both the surfaces of the AR films are damaged and surrounding the injured speckles of the substrate there are flake-like injury. In the course of this injury, the effects of heat and thermal stress are the main factors that produce injury, and the corresponding mechanism is analyzed to explain the phenomenon.To carry out the repeatability test of the same kinds of dielectric films laser induced damage threshold. The results show that the damage threshold of the AR films of 90286 type and the HR films of 90283 type have a strong consistency.Linear Fitting and Non-linear fitting are used to fit the damage threshold The linear distribution of the test results of the samples use Linear Fitting method and the deviated from the straight-line type distribution use Non-linear fitting method which results are more consistent with the actual situation.The damage configuration and the extent of injury of the dielectric film under the irradiation of long-pulse laser are respectively compared with those induced by short-pulse laser. It is concluded that long-pulse laser could damage both the layers and the substrate at the same time while short-pulse laser could only damage the surface of the layers.The results of this paper may provide references for the researches on the process and mechanism of the interaction between long-pulsed laser and materials as well as the laser machining process.