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Cadmium oxide (CdO) has recently attracted attention as a material with controllable properties tailored for optoelectronic and nanophotonic devices due to its superior mobility. However, its potential application in near-infrared (NIR) remains to be explored. In this work, we demonstrate that the epsilon-near-zero (ENZ) wavelength and nonlinear optical properties of CdO films can be effectively tuned by Mo doping. The results show that Mo doping increases the electron concentration as well as improve the crystalline quality of CdO. With increasing Mo doping, we achieve blueshifts of the ENZ wavelength from 2.89 to 1.56 μm. The nonlinear absorption (NLA) behavior at 1550 nm changes from reverse saturable absorption to saturable absorption with increasing Mo content. Moreover, significant improvement in NLA performance with nonlinear absorption coefficient β = −72 cm/GW is observed at the highest doping content. Our work shows that doped CdO films with tunable optoelectrical and nonlinear optical properties can be an ideal candidate for optoelectronic and nanophotonic application in the NIR region. [ABSTRACT FROM AUTHOR]

We design and numerically investigate a wide angle and broadband perfect absorber with compact multilayer structures. The proposed structure is composed of three stacks of semiconductor films and one metal layer. The absorber presents a broadband absorption between 450 nm and 700 nm with an average absorption above 99.2%. For oblique incidence, the absorber shows an average absorption about 90% for a wide range of incident angles from 0 to 60 with p polarization and s polarization. The electrical field intensity distributions are also studied to disclose the broadband absorption mechanism. This designed broadband absorber appears to have very promising applications in solar thermal energy harvesting, thermal emitters and detection. [ABSTRACT FROM AUTHOR]

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]

A broadband, polarization-independent, and wide angle metamaterial absorber (MA) with tapered cylinder structures is investigated with finite difference time domain simulations. The titanium nitride (TiN) and indium tin oxide (ITO) thin film are introduced as the tapered cylinder structures. The unit cell structure is mainly composed of two pairs of TiN/ITO layers and one TiN base layer. The absorption is higher than 99% between the wavelength 700 nm and 1000 nm. The broadband, polarization independent average absorption remains above 95% between 400 nm and 1200 nm with a wide range of incident angles from 0° to 40°. The electrical field intensity distributions are studied to disclose the broadband absorption mechanism. This designed broadband absorber appears to be very promising applications in the plasmonic sensing and photovoltaic devices. [ABSTRACT FROM AUTHOR]

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 on BK7 substrates by e-beam evaporation with different deposition parameters such as substrate temperature (323–623K), oxygen pressure (0.5–3.0×10−2 Pa) and deposition rate (0.2–0.5nm/s). Absorption, scattering and chemical composition were investigated by surface thermal lensing (STL) technique, total integrated scattering (TIS) measurement and X-ray photoelectron spectroscopy (XPS), respectively. The laser-induced damage threshold (LIDT) was assessed using pulsed Nd:YAG 1064nm laser at a pulse length of 12ns. The results showed that optical properties, absorption and LIDT were influenced by the deposition parameters and annealing. However, scattering was little correlated with the deposition parameters. On the whole, the LIDT increased with increasing substrate temperature and oxygen pressure, whereas it increased firstly and then decreased upon increasing deposition rate. After annealing at 673K for 12h, the LIDT of films improved significantly. The dependence of possible damage mechanism on deposition parameters was discussed. [Copyright &y& Elsevier]

Abstract: Zirconium dioxide (ZrO2) thin films were deposited on BK7 glass substrates by the electron beam evaporation method. A continuous wave CO2 laser was used to anneal the ZrO2 thin films to investigate whether beneficial changes could be produced. After annealing at different laser scanning speeds by CO2 laser, weak absorption of the coatings was measured by the surface thermal lensing (STL) technique, and then laser-induced damage threshold (LIDT) was also determined. It was found that the weak absorption decreased first, while the laser scanning speed is below some value, then increased. The LIDT of the ZrO2 coatings decreased greatly when the laser scanning speeds were below some value. A Nomarski microscope was employed to map the damage morphology, and it was found that the damage behavior was defect-initiated both for annealed and as-deposited samples. The influences of post-deposition CO2 laser annealing on the structural and mechanical properties of the films have also been investigated by X-ray diffraction and ZYGO interferometer. It was found that the microstructure of the ZrO2 films did not change. The residual stress in ZrO2 films showed a tendency from tensile to compressive after CO2 laser annealing, and the variation quantity of the residual stress increased with decreasing laser scanning speed. The residual stress may be mitigated to some extent at proper treatment parameters. [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: Antireflection coatings at the center wavelength of 1053nm were prepared on BK7 glasses by electron-beam evaporation deposition (EBD) and ion beam assisted deposition (IBAD). Parts of the two kinds of samples were post-treated with oxygen plasma at the environment temperature after deposition. Absorption at 1064nm was characterized based on surface thermal lensing (STL) technique. The laser-induced damage threshold (LIDT) was measured by a 1064-nm Nd:YAG laser with a pulse width of 38ps. Leica-DMRXE Microscope was applied to gain damage morphologies of samples. The results revealed that oxygen post-treatment could lower the absorption and increase the damage thresholds for both kinds of as-grown samples. However, the improving effects are not the same. [Copyright &y& Elsevier]

Abstract: With the present work we tried to study the effective methods to improve the laser-induced damage threshold (LIDT) and reflectance of HR coatings at 355nm. The work presented in this paper was part of an ongoing study about vacuum annealing. It was dedicated to study the effects of vacuum annealing with different temperature gradients on the structure, optical properties and laser-induced damage threshold (LIDT) of 355nm Al2O3/MgF2HR coatings. A number of samples were prepared by electron beam evaporation using the same deposition process with an optimal deposition temperature of 280°C. After deposition, samples were annealed in the coating chamber for 3h with different temperature gradients. Morphologies of the samples were observed by Leica-DMRXE Microscope. Structure of the samples had been characterized by X-ray diffraction (XRD). Transmittance and reflectance of the samples were measured by Lambda 900 Spectrometer. The LIDT of the samples was measured by a 355nm Nd:YAG laser with a pulse width of 8ns. It was found that the temperature gradient of vacuum annealing had significant effects on the morphology, structure, absorption, and LIDT of the samples. [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]

Based on the electron beam evaporation with oxygen plasma assistance, Y 2 O 3 films were prepared at different deposition temperatures and oxygen flow rates. X-ray diffraction showed that all deposited Y 2 O 3 films had cubic phase with (2 2 2) plane preferred orientation. Spectrometer test results showed that water absorption decreases in transmittance and reflectance around the wavelength of 2.9 μm. According to Lorentz dispersion theory, a multi-oscillator model was established to calculate optical constants and the inhomogeneity of Y 2 O 3 films in the wavelength range from 2.5 to 4 μm. The results indicate an abnormal dispersion phenomenon is appearing in the 2.5–4 μm wavelength region. It was found that under the same oxygen flow rate, higher substrate temperature leads to a greater refractive index and smaller extinction coefficient. When the oxygen flow rate is increased at the same substrate temperature, the extinction coefficient remains almost unchanged, while the refractive index decreases. In addition, the refractive index and the inhomogeneity of the films increase almost linearly as the grain size increases. • Based on electron beam evaporation technology, cubic Y2O3 films were prepared under different deposition conditions. • Based on Lorentz multi-oscillator model, a method for calculating the optical constants was proposed. • The water absorption characteristics of cubic Y2O3 films in the wavelength range from 2.5 to 4 um were studied. • The relationship between the grain size, the refractive index and the inhomogeneity has been found. [ABSTRACT FROM AUTHOR]