Fabrication and investigation of high reflectivity mirrors for laser systems

Fabrication and Investigation of High Reflectivity Mirrors for Laser Systems In this work, two different types of mirrors were fabricated and studied. In the first part, the focus was placed on formation of high reflectivity mirrors for high power laser systems. Laser induced damage is the main limitation in production and application of femtosecond lasers. Novel sculptured thin film technology was suggested in order to solve this problem. By changing the refractive index of the same material using glancing angle deposition technique it is possible to obtain interference of optical coatings using only one material. This allows eliminating the second material, which usually limits laser damage resistance. High reflectivity mirrors containing all silica layers (dense and porous) were produced by electron beam evaporation. Optical and structural properties of these mirrors fabricated under different deposition conditions were investigated. It was found, that optimal deposition rate for SiO2 sculptured thin films is much higher than usually used one for conventional layers. Characterization of mirrors demonstrated higher than 99% reflectance in UV spectral region. Despite high quality, these mirrors were sensitive to atmosphere influence. Thus, the spectral performance of SiO2 mirrors for future applications in laser systems should be investigated in detail. The second part of this work is concentrated to the optimization of technological conditions of semiconductor Bragg mirrors for quantum structures based IR light sources. A series of Bragg mirrors containing GaAs and AlAs layers were grown using molecular beam epitaxy. As/III element group flux ratio was found to be crucial parameter for the growth. Optical, AFM and XRD measurements of samples showed the reflectance in NIR spectral region of almost 100%, low surface roughness (~1 nm) and good crystalline structure. These Bragg mirrors will be further used for fabrication of vertical cavity surface emitting semiconductor lasers