Thermal Damage Characteristics in Optical Multilayer Films Resulting from Exposure to a Repetitively Pulsed Laser Beam
F.L. Chen, D.H. Li and P. Hu
Based on standing-wave theory, a theoretical model with high energy absorption at the surface and interfaces is developed to calculate the temperature distribution evolving with time in optical multilayer films under irradiation of repetitively pulsed laser. As an example, a type of high reflectance (HR) multilayer film is examined and multi-spike temperature profiles in the film are observed. It is found that in time order of nanoseconds, the overall heating effect and thermal damage of a repetitively pulsed laser is equivalent to that of a single pulse laser which has same energy fluence and irradiation duration. For laser of constant total fluence, because of thermal diffusion, the longer the pulse duration is, the lower the maximum temperature rise will be in the film. For incident laser at different wavelengths, the temperature profiles and damage thresholds of the multilayer exhibit significant difference.
Keywords: Laser beam, optical multilayer, film, repetitively pulsed, thermal damage, heating, standing-wave theory, temperature distribution