Search

Abstract: The mechanism of improving 1064nm, 12ns laser-induced damage threshold (LIDT) of TiO2/SiO2 high reflectors (HR) prepared by electronic beam evaporation from 5.1 to 13.1J/cm2 by thermal annealing is discussed. Through optical properties, structure and chemical composition analysis, it is found that the reduced atomic non-stoichiometric defects are the main reason of absorption decrease and LIDT rise after annealing. A remarkable increase of LIDT is found at 300°C annealing. The refractive index and film inhomogeneity rise, physical thickness decrease, and film stress changes from compress stress to tensile stress due to the structure change during annealing. [Copyright &y& Elsevier]

Abstract: The laser-induced damage of Ta2O5 films annealed at a wide range of temperature (473–1273K) at the laser wavelengths of 1064 and 355nm was investigated. The relations between microstructure, optical properties, chemical composition, absorption and laser-induced damage threshold (LIDT) were studied. The dependence of a damage mechanism on laser wavelengths was discussed. It was found that the LIDT either at 1064 or 355nm first increased and then decreased with increase of annealing temperature. The LIDT at 1064nm was influenced by the substoichiometric defects, structural defects and thermal diffusion, whereas at 355nm it was affected mainly by the intrinsic absorption and structural defects. Both the maximum LIDT at the two wavelengths were obtained at the annealing temperature of 873K, which could be attributed to the lowest defect density in films. [Copyright &y& Elsevier]

Abstract: Ta2O5 films were deposited using the conventional electron beam evaporation method and then annealed at temperatures in the range 373–673K. Chemical composition, scattering and absorption were examined by X-ray photoelectron spectroscopy (XPS), total integrated scattering (TIS) measurement and the surface thermal lensing (STL) technique, respectively. The laser-induced damage threshold (LIDT) was assessed using the output from an Nd:YAG laser with a pulse length of 12ns. The results showed that the improvement of the LIDT after annealing was due to the reduced substoichiometric and structural defects present in the film. The LIDT increased slightly below 573K and then increased significantly with increase in annealing temperature, which could be attributed to different dominant defects. Moreover, the root mean square (RMS) roughness and scattering had little effect on the LIDT, while the absorption and the LIDT were in accord with a general relation. [Copyright &y& Elsevier]

Abstract: Ta2O5 films were deposited by conventional electron beam evaporation method and then annealed in air at different temperature from 873 to 1273K. It was found that the film structure changed from amorphous phase to hexagonal phase when annealed at 1073K, then transformed to orthorhombic phase after annealed at 1273K. The transmittance was improved after annealed at 873K, and it decreased as the annealing temperature increased further. The total integrated scattering (TIS) tests and AFM results showed that both scattering and root mean square (RMS) roughness of films increased with the annealing temperature increasing. X-ray photoelectron spectroscopy (XPS) analysis showed that the film obtained better stoichiometry and the O/Ta ratio increased to 2.50 after annealing. It was found that the laser-induced damage threshold (LIDT) increased to the maximum when annealed at 873K, while it decreased when the annealing temperature increased further. Detailed damaged models dominated by different parameters during annealing were discussed. [Copyright &y& Elsevier]

Abstract: Al2O3/SiO2 films have been prepared by electron-beam evaporation as ultraviolet (UV) antireflection coatings on 4H-SiC substrates and annealed at different temperatures. The films were characterized by reflection spectra, ellipsometer system, atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. As the annealing temperature increased, the minimum reflectance of the films moved to the shorter wavelength for the variation of refractive indices and the reduction of film thicknesses. The surface grains appeared to get larger in size and the root mean square (RMS) roughness of the annealed films increased with the annealing temperature but was less than that of the as-deposited. The Al2O3/SiO2 films maintained amorphous in microstructure with the increase of the temperature. Meanwhile, the transition and diffusion in film component were found in XPS measurement. These results provided the important references for Al2O3/SiO2 films annealed at reasonable temperatures and prepared as fine antireflection coatings on 4H-SiC-based UV optoelectronic devices. [Copyright &y& Elsevier]

Abstract: TiO2 coatings were prepared on fused silica with conventional electron beam evaporation deposition. After TiO2 thin films were annealed at different temperatures for 4h, several properties were investigated by X-ray diffraction (XRD), spectrometer, photoelectron spectroscopy (XPS) and AFM. It was found that with the annealing temperature increasing, the transmittance of TiO2 coatings decreased, and the cutoff wavelength shifted to long wavelength in near ultraviolet band. Especially, when coatings were annealed at high temperature, the optical loss is very serious, which can be attributed to the scattering and the absorption of TiO2 coatings. XRD patterns revealed that only anatase phase was observed in TiO2 coatings regardless of the different annealing temperatures. XPS results indicated that the fine chemical shift of TiO2 2p1/2 should be attributed to existence of oxygen vacancies around Ti+4 ion. The investigation on surface morphology by AFM showed that the RMS of titania thin films gradually increases from less than 0.40nm to 5.03nm and it should be ascribed to the growth of titanium dioxide grain size with the increase of annealing temperature. [Copyright &y& Elsevier]

Abstract: Zinc oxide (ZnO) films with c-oriented were grown on fused quartz glass substrates at room temperature using dc reactive magnetron sputtering. The as-grown films were annealed at 700°C in air and bombarded by ion beam, respectively. The effects of post-treatments on the structural and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. The XRD spectra indicate that the crystal quality of ZnO films has been improved by both the post-treatments. Compared with the as-grown sample, both annealed and bombarded samples exhibited blueshift in the UV emission peaks, and a strong green emission was found in the annealed ZnO film. In both optical transmittance and absorption spectra, a blueshift of the band-gap edge was observed in the bombarded film, while a redshift was observed in the annealed film. [Copyright &y& Elsevier]

ZrO2 coatings were deposited on different substrates of Yb:YAG and fused silica by electron beam evaporation. After annealed for 12 h at 673 and 1073 K, respectively, weak absorption of coatings was measured by surface thermal lensing (STL) technique, and then laser-induced damage threshold (LIDT) was determined also. The crystalline phase of ZrO2 coatings and the size of the crystal grain were investigated by X-ray diffraction. It was found that microstructure of ZrO2 coatings was dependent on both annealing temperature and substrate structure, and coatings containing monoclinic phases had higher damage threshold than others. Due to the strong absorption of Yb:YAG, damage threshold of coatings on Yb:YAG was much less than that on fused silica. [Copyright &y& Elsevier]

The effects of annealing on structure and laser-induced damage threshold (LIDT) of Ta2O5/SiO2 dielectric mirrors were investigated. Ta2O5/SiO2 multilayer was prepared by ion beam sputtering (IBS), then annealed in air under the temperature from 100 to 400 °C. Microstructure of the samples was characterized by X-ray diffraction (XRD). Absorption of the multilayer was measured by surface thermal lensing (STL) technique. The laser-induced damage threshold was assessed using 1064 nm free pulsed laser at a pulse length of 220 μs.It was found that the center wavelength shifted to long wavelength gradually as the annealing temperature increased, and kept its non-crystalline structure even after annealing. The absorbance of the reflectors decreased after annealing. A remarkable increase of the laser-induced damage threshold was found when the annealing temperature was above 250 °C. [Copyright &y& Elsevier]