Abstract
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.
Highlights
High-performance components for precision-optics applications require thin films with perfect optical properties, as well as minimal mechanical stress
To fabricate multilayer coatings with optimizing optical and mechanical properties, it was necessary to investigate the performances of the deposited TiO2 and SiO2 single layers
The physical thickness and optical constants (n, k) of the TiO2 film were determined from a spectrophotometric measurement
Summary
High-performance components for precision-optics applications require thin films with perfect optical properties, as well as minimal mechanical stress. It is crucial to select the coating materials and the deposition technology very carefully. Conventional electron-beam evaporation (EBE) remains the preferred vacuum coating technology for nanosecond pulsed laser devices [1,2]. Plasma ion-assisted deposition (PIAD) and magnetron sputtering (MS) have been successfully employed for femtosecond laser systems [3,4]. Ion-beam sputtering (IBS) has been comprehensively demonstrated for the preparation of high reflectivity and ultralow-loss films in the advanced gravitational waves interferometers [5,6]. With the development of vacuum-coating technology, the complexity of thin films has significantly increased, and mechanical stress control has become a major challenge. The optimization of mechanical stress is very much necessary for the better performance of optical coatings
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