According to the parameter requirements of a graded reflectivity mirror with a Gaussian profile, the layer structure and the mask pattern are designed using a graded-thickness middle layer. The mask and the automatic mask-switchover equipment are designed considering the actual requirement of the thin films and the specific deposit facility. The uniformity of the layer thickness is analyzed. The measurement results indicate that samples prepared with this technique are basically in accordance with the design parameter. The scattering effect between the material molecules and the mask, thickness errors, and the alignment error between the mask and the substrate are the main factors that influence the deposit result.
ZrO2 thin films were deposited using an electron beam evaporation technique on two kinds of LiB3O5 (LBO) substrates having the surfaces prepared by cutting at specified crystalline orientations. The results tested by the spectrophotometer indicated that all films had optical anisotropy, which was attributed to the film microstructure with preferred orientation from GXRD (grazing X-ray diffraction) analysis. The film microstructure difference deposited on LBO substrates with different crystalline orientation resulted in film refractive index change, namely, the ZrO2 thin film with the m-(-212) preferred orientation had lower refractive index than that with the o-(130) preferred orientation.
The ZrO2 thin films were deposited on BK7 glass substrates by electron beam evaporation method at room temperature. The influences of post-deposition annealing between 200°C and 400°C on the structural and mechanical properties of the films have been investigated by X-ray diffraction and atomic force microscopy. It was found that a monoclinic phase formed at lower temperature of 200°C. With the increase of the annealing temperature, the tetragonal phase appeared. The stress in ZrO2 films showed a transition from tensile to compressive which could be explained as the evolution of the microstructure as function of annealing temperatures. At the same time, the refractive index of the ZrO2 films increased with the increasing of annealing temperatures, which may be ascribed to the microstructure densification of the ZrO2 films.
Single layers of Al2O3 and MgF2 were deposited upon super polished fused-silica by electron-beam evaporation and were characterized. The subsequent optical constants n and k were reported for the spectral range of 180nm-230nm. And HR coatings for 193nm were designed on the basis of the evaluated optical constants and produced. Transmittance and reflectance of HR coatings were compared to the theoretical calculations on the basis of the evaluated optical constants of the single layers.
The periodic dielectric phase retarders that produce a ±90° phase shift between the p- and s- polarization components at the incident angle of 54° and the wavelength of 1315nm while maintaining high reflectivity for both components are designed. An optimization technique has been used to determine the layer thickness for a coating design that produce a 270±1° phase shift between the p- and s- polarization components over 1285-1345nm while the average reflectivity is over 99.5%. Then the designed retarders were prepared by ion beam sputtering (IBS), and the phase shift was 262.4±1.8° and the reflectivity was over 99.6% at the design waveband.
Laser conditioning effects of the dielectric oxide mirror coatings with different designs were investigated. Simple quarter-wave ZrO2:Y2O3/SiO2 mirrors and half-wave SiO2 over-coated ZrO2:Y2O3/SiO2 mirror coatings at 1064nm were fabricated by E-beam evaporation (EBE). The absorbance of the samples before and after laser conditioning was measured by surface thermal lensing (STL) technology and the defects density was detected under Nomarski microscope. The enhancement of the laser damage resistance was found after laser conditioning. The dependence of the laser conditioning on the coating design was also observed and the over-coated sample obtained greatest enhancement, whereas the absorbance of the samples did not change obviously.