Study On Laser Damage Properties Of Optical Dielectric Films

The optical thin film components are important parts of the laser systems. For large-power and high-energy laser systems, the laser damage resistance ability of films is also one of the bottlenecks of the development of these systems. Moreover, the thin film components are important parts of the infrared windows and the guide-heads of tactical missile. Once the thin film components are damaged by a high energy laser weapon, the whole optical system may be destroyed. Thus, it is important to improve the laser-induced damage threshold of the thin films for the development of high power laser systems and enlarging of the application of scientific research and production. Meanwhile it is of the theoretical principle to develop the high-energy laser weapon.In order to optimizing materials, laser damage characteristic of the various dielectric materials are investigated by using a set of laser-induced damage threshold (LIDT) testing system., The factors which are film materials, film thickness, and laser wavelength and pulse width influence the LIDT of thin films by studying damage mechanism. Base on literatures analyzing, material characteristics contrasting, it is showed that: a. the material with a higher band gap commonly has a higher LIDT; b. for most materials, the LIDT of films may be positive correlative with melting point and mechanical strength.Several single-layer dielectric thin films such as HfO2, ZrO2 and SiO2 are prepared by ion-beam-assisted deposition (IBAD) on K9 substrate. The damage threshold and damage morphology of these thin films are tested with 1-on-1 testing method, He-Ne laser scattering, phase contrast microscope damage checking method and 1.064μm Q switch Nd:YAG laser system with 10ns pulse width. The results are as following:the deposition rate is the major factor to damage threshold for HfO2, ZrO2 and SiO2. The damage threshold of HfO2 thin-film increases with the deposition rate first, and then decrease; the largest damage threshold prepared with HfO2 is 4.25J/cm2. After annealing, the damage threshold of these films significantly increases; damage morphology analysis shows that the laser damage resistance ability of HfO2 thin film is higher than that of ZrO2 under the same laser energy. In this paper, other materials such as MgF2, BaF2 and YF3 are also studied. The results indicate that for the same laser energy, the film materials are YF3, BaF2 and MgF2 according to their resistance capability to laser. Finally, the optimum process parameters of HfO2, SiO2, MgF2, BaF2 and YF3 are obtained through the relationship between damage threshold and experiment parameters.