Mechanism for 355 nm nanosecond-pulse-driven damage in HfO_2/SiO_2 high reflectivity coating

摘要

The effect of oxygen vacancy on the laser-induced damage behaviors of HfO_2/SiO_2 high reflective coating was investigated by single 355nm-8ns laser. The oxygen vacancy was tuned by controlling the oxygenation of the outmost HfO_2 layer during the deposition procedure. The reflectivity of the coating with higher oxygen vacancy drops by 0.2% and the damage threshold drops by 60%, compared with the normal coating. Damage morphologies of samples were obtained by optical microscope, AFM, SEM and FIB technology. Typical morphologies of these coatings show little difference. Average oxygen vacancy of single HfO_2 layer prepared on the BK7 substrate measured by XPS is about 43%. Theoretical analysis with a nonlinear thermodynamics model shows that the damage can be attributed to nonlinear thermal process. Moreover, the size of damage crater can be interpreted by a mechanics model.