A straightforward theoretical routine is proposed to design shadowing masks which are used for preparing uniform coatings on flat as well as strongly curved spherical substrates with large diameters in planetary rotation system. By approximating a spherical substrate in planetary rotation to a corresponding flat substrate in simple rotation around the revolution axis, the initial shape of a shadowing mask is determined. The desired uniformity for the spherical substrate is further realized through expanding appropriately the arc length of the initial shadowing mask. Utilizing the shadowing masks designed with the theoretical routine, film uniformities better than 97% are experimentally achieved for large-diameter spherical substrates with ratios of clear aperture to radius of curvature range from approximately −1.0 to 1.3.

Optical and mechanical properties of multilayer coatings depend on the selected layer materials and the deposition technology; therefore, knowledge of the performances of thin films is essential. In the present work, titanium dioxide (TiO₂) and silicon dioxide (SiO₂) thin films have been prepared by plasma ion-assisted deposition (PIAD). The optical, structural, and mechanical properties of thin films have been investigated using spectrometer/ellipsometer, X-ray diffraction (XRD), atomic force microscopy (AFM), and laser interferometer. The results show that TiO₂ film fabricated by PIAD induces a high refractive index, wide optical band gap, amorphous structure, smooth surface, and tensile stress. In the case of SiO₂ film, high bias voltage leads to dense structure and compressive stress. As an application, a three-wavelength high reflectance at 632.8, 808, and 1550 nm was optimized and deposited. The dependence of total stress in the multilayer on the substrate temperature was studied as well. In conclusion, it was demonstrated that PIAD is an effective method for the preparation of ultralow stress TiO₂/SiO₂ multilayer films. The achieved stress was as low as 1.4 MPa. The result could provide guidance to the stress optimization of most optical components without prefiguring, backside coating, and postdeposition treatments.

HfO₂ thin films are extensively applied in optical coatings and microelectronic devices. However, film defects, which are vital to the performance of the thin films, are still under intense investigation. In this work, the absorption, photoluminescence, and crystallization characteristics of HfO₂ films prepared by electron-beam evaporation and ion-assisted deposition are investigated in detail. Experimental results showed that high-temperature thermal annealing in air resulted in a reduced absorption coefficient, an increased bandgap width, and an increased degree of crystallization. After thermal annealing, an absorption shoulder near 5.8 eV was caused by excitons in the films, which were independent of oxygen vacancy defects and crystallization. Under 6.4 eV (193 nm) laser excitation, the photoluminescence spectrum showed five emission peaks for HfO₂ films both with and without thermal annealing. The emission peak near 4.4 eV was generated by the self-trapped exciton, and the peak near 4.0 eV was related to the OH group in the film. The oxygen vacancy defect-induced absorption of HfO₂ films in a broad spectral range significantly increased when HfO₂ film was re-annealed in Ar gas after first being annealed in air, while the photoluminescence spectrum showed no significant change, indicating that the emission peaks at 2.3, 2.8, and 3.4 eV were not related to oxygen vacancy defects.

A model taking into consideration the refractive index inhomogeneity and surface roughness of a film was proposed for the simultaneous determination of the optical constants, thickness, and surface roughness of a single-layer thin film from spectrophotometric measurements. In the model, the rough surface was treated as an effective absorbing layer. The model was applied to determine simultaneously the parameters of single-layer ${\mathrm{MgF}}_2$ thin films deposited on fused silica substrates by the oblique-angle deposition technique. The film thicknesses and rms surface roughnesses extracted from spectrophotometric measurements with the proposed model were in good agreement with the values measured by a spectroscopic ellipsometer and an atomic force microscope, respectively.

For a coating machine with a planetary rotation system and counterrotating shadowing mask configuration, a shadowing mask was designed using a numerical optimization algorithm to control the thickness uniformity of optical coatings formed on conical substrate. Single-layer magnesium fluoride (${\mathrm{MgF}}_2$) and antireflective (AR) coating at 193 nm were fabricated on a convex conical substrate holder (with diameter 225 mm, apex angle 140 deg, and height 41 mm) by thermal evaporation. Thickness distribution determined from the transmittance spectra of single-layer ${\mathrm{MgF}}_2$ thin films on BK7 slices showed that uniformities better than 99.3% were experimentally achieved with the designed counterrotating shadowing mask. From the reflectance spectra, uniform optical performance was also obtained for the 193 nm AR coating deposited on fused-silica substrates.