Band-gap and refractive index are known as fundamental properties determining intrinsic optical resistance of multilayer dielectric coatings. By considering this fact we propose novel approach to manufacturing of interference thin films, based on artificial nano-structures of modulated porosity embedded in high band-gap matrix. Next generation all-silica mirrors were prepared by GLancing Angle Deposition (GLAD) using electron beam evaporation. High reflectivity (HR) was achieved by tailoring the porosity of highly resistant silica material during the thin film deposition process. Furthermore, the proposed approach was also demonstrated to work well in case of anti-reflection (AR) coatings. Conventional HR HfO2 and SiO2 as well as AR Al2O3 and SiO2 multilayers produced by Ion Beam Sputtering (IBS) were used as reference coatings. Damage performance of experimental coatings was also analyzed. All-silica based GLAD approach resulted in significant improvement of intrinsic laser damage resistance properties if compared to conventional coatings. Besides laser damage testing, other characteristics of experimental coatings are analyzed and discussed – reflectance, surface roughness and optical scattering. We believe that reported concept can be expanded to virtually any design of thin film coatings thus opening a new way of next generation highly resistant thin films well suited for high power and UV laser applications.
Laser resistance of optical elements is one of the major topics in photonics. Various routes have been taken to improve optical coatings, including, but not limited by, materials engineering and optimisation of electric field distribution in multilayers. During the decades of research, it was found, that high band-gap materials, such as silica, are highly resistant to laser light. Unfortunately, only the production of anti-reflection coatings of all-silica materials are presented to this day. A novel route will be presented in materials engineering, capable to manufacture high reflection optical elements using only SiO2 material and GLancing Angle Deposition (GLAD) method. The technique involves the deposition of columnar structure and tailoring the refractive index of silica material throughout the coating thickness. A numerous analysis indicate the superior properties of GLAD coatings when compared with standard methods for Bragg mirrors production. Several groups of optical components are presented including anti-reflection coatings and Bragg mirrors. Structural and optical characterisation of the method have been performed and compared with standard methods. All researches indicate the possibility of new generation coatings for high power laser systems.
The stresses in thin films are one of the main problems in the development of small dimensions or thin optical components. In order to produce low-tension anisotropic coatings, the characterization of serial bideposition is essential. Structural and optical performance have been tested for anisotropic TiO2 thin films deposited by serial bideposition technique. Three-dimensional surface interferometric measurements were performed for samples deposited at various angles. Also experimental observations of anisotropic tensions in annealed two-dimensional sculptured thin films of TiO2 material are presented. The deposition angle of 80 deg is considered to be the most applicable for developing optical components due to the befitting optical performance and the lowest tensions before and after the annealing.
We report optical characterization of the different optical components fabricated in transparent materials by bulk refractive index modification or surface ablation by femtosecond pulses. The methods used for characterization of the components with refractive index modification fabricated in fused silica by high repetition rate femtosecond KGW:Yb laser were transmission and diffraction measurements at 532 and 632.8 nm wavelengths, and total integrated scattering (TIS) at 532 mn wavelength. The combined characterization methods were sufficient for modification process optimization and allowed creation of the Bragg gratings with diffraction efficiency in range from 55 to 90% and low scattering losses. The forward and backward TIS measurements of the radial polarization converter showed that forward scattering is more than five times as high as backward scattering. Solar cells with modified surface by femtosecond pulse ablation were investigated by TIS and Volt-Ampere measurements. The current increase is registered with growth of the scattering loses in the solar cells.