Study On Thermal Distortion And Weak Absorption Of Thin Film Coatings Irradiated By 10.6 μm Laser

The absorption of optical thin film coatings is one of the main factors that limit the development of high-power lasers. It not only affects the optical quality of thin film, but also makes heat deposit in thin film. Especially for high-power laser, even the very weak absorption in thin film is high enough to result in catastrophic damage. Thus, it is necessary to measure the mean and local absorption of the optical thin film coatings accurately, fast and in-situ.At present, photothermal deflection technology and surface thermal lensing technology are widely applied in weak absorption measurement. The wavelength of laser for researching is concentrated on the ultraviolet, near infrared and visible light, whereas the wavelength in the range of middle infrared and far infrared is little researched. Furthermore, as the high-power CO2 laser is widely used, especially the development of the research on CO2 laser propagating in atmosphere and window material in infrared band, the research on the surface thermal distortion in optical thin film irradiated by 10.6 m laser is more and more important.In this thesis, the thermal distortion and the weak absorption of thin film samples irradiated by 10.6 m CO2 laser were studied. The main work is asfollows:1. The physical model of the temperature field of multiplayer filmsirradiated by 10.6 m CO2 laser was built. The numerical calculation code was built up and confirmed by the calculating results of the Stanford University, showing the validity and credibility.2. The temperature fields of the single-layer and multiplayer films irradiated by 10.6 m CO2 laser have been simulated and analyzed.3. By using the Shack-Hartmann wavefront sensor, the thermal distortion of the substrate, the single-layer dielectric thin films with different thickness, and the multilayer dielectric thin films with different multilayer thin films ( YbF3/ ZnSe) irradiated by CO2 laser were studied experimentally.4. The experimental setups have been built in the use of the photothermal deflection technology and surface thermal lensing technology, respectively. The weak absorption of different optical thin films has been measured. The experimental results obtained from the above two methods were compared.The results obtained in this thesis would be of both theoretical significance and practical interest in the fabrication of thin films.