Search

Abstract: Laser damage behaviors of thin-film beam splitters for third harmonic separation were investigated under the simultaneous exposure of fundamental frequency (1ω) and the third harmonics laser beam (3ω). The samples were prepared by conventional e-beam evaporation, and the surface laser-induced damage thresholds (LIDT) of the samples were obtained for the irradiations of 3ω only and 3ω with various fluence of 1ω. It was found that external 1ω can raise damage probability of multilayer films; the higher the 1ω energy density, the lower the damage threshold. Additionally, numerical simulation of damage probability was given for the simultaneous exposure to two beams. [Copyright &y& Elsevier]

Abstract: The TiO x thin films were prepared by electron beam evaporation using TiO as the starting material. The effect of the annealing temperature on the optical and electrical properties was investigated. The spectra of X-ray photoelectron spectroscopy reveal that Ti in the films mainly exist in the forms of Ti2+ and Ti3+ below 400°C 24h annealing. The charge transfer between different titanium ion contribute greatly to the color, absorption, and electrical resistance of the films. [Copyright &y& Elsevier]

Abstract: A series of ZnO thin films were deposited on ZnO buffer layers by DC reactive magnetron sputtering. The buffer layer thickness determination of microstructure and optical properties of ZnO films was investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. XRD results revealed that the stress of ZnO thin films varied with the buffer layer thickness. With the increase of buffer layer thickness, the band gap edge shifted toward longer wavelength. The near-band-edge (NBE) emission intensity of ZnO films deposited on ZnO buffer layer also varied with the increase of thickness due to the spatial confinement increasing the Coulomb interaction between electrons and holes. The PL measurement showed that the optimum thickness of the ZnO buffer layer was around 12nm. [Copyright &y& Elsevier]

Abstract: ZnO:Zn phosphor thin films were prepared by face-to-face annealing at 450°C in air. The effects of the face-to-face annealing on the structural and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. Measurement results showed that the crystal quality of ZnO films was improved by face-to-face annealing. Both UV light emission and visible light emission were enhanced compared to those of open annealing films. The UV emission peak was observed to have a blueshift towards higher energy. The optical band-gap edge of as-annealed films shifted towards longer wavelength. [Copyright &y& Elsevier]

Abstract: The refractive indices of thin films, containing dielectric and voids in an oblique columnar structure, are modeled by extended effective medium in the quasi-static limit. The dielectric function is shown to be strongly dependent on the angle of incidence and on the columnar orientation for p-polarized light. This model is applied to model ZrO2 thin films with oblique columnar structures and the computed results, with the Maxwell Garnett, the Bragg–Pippard, and the Bruggeman formalisms, have been given. [Copyright &y& Elsevier]

Indium tin oxide (ITO) has important application in photoelectronic and photonic devices, demanding effective approach and appropriate parameters to modulate the ITO properties. The effects of laser annealing at 1064 nm with different pulse width (875 ps, 10 ns, and 300 ns) on optical and nonlinear optical properties of ITO films were investigated. Compared with 875 ps and 10 ns, laser annealing at 300 ns significantly improved the near-infrared transmittance of ITO films. The change arises from the elimination of oxygen vacancies and reduction of tin oxides, resulting in the decrease of carrier concentration. Finite element simulations indicate that laser annealing with pulse width of 875 ps and 10 ns have high instantaneous peak temperatures of 1128.5 K and 783 K, respectively, while the temperature accumulation between pulses is negligible. On the contrary, the laser annealing with a pulse width of 300 nshas lower peak transient temperature of 343 K but high static residence temperature of 973 K. The results reveal that the modification of ITO films depends more on the static average temperature rather than the instantaneous peak temperature. The modulation of carrier dynamics in both amplitude and temporal domain was demonstrated after 300 ns laser annealing, achieving ultrafast transient response approximately 150 fs. This work provides theoretical and experimental basis for us to select suitable laser conditions for directional annealing of ITO film to make it suitable for the applications of broad optical spectrum photovoltaic devices or ultrafast optical exchange for high-speed data processing. • Laser annealing (LA) is shown for three pulse widths at approximately 0.2 J/cm2. • LA at 300 ns significantly improves the near-infrared transparency due to the reduction of carrier absorption. • Tailorable amplitude and time scale of carrier transient response are achieved by LA, with ultrafast response time 150 fs. • The modification of ITO properties depends on the static temperature rather than transient peak temperature. [ABSTRACT FROM AUTHOR]

Different laser damage testing protocols, including 1-on-1, S-on-1, and Raster Scan, were conducted on 532 nm polarizers to evaluate the damage resistance and mechanisms. A comparison of the laser-induced damage thresholds (LIDTs) revealed different damage characteristics and major contributions to film failure for different polarizations. For P polarization, the LIDTs for the three test protocols were nearly the same because of the stabilization of two typical damage morphologies of flat-bottomed pits and mussel damage pits. For S polarization, the LIDTs for multiple pulses were lowest, where absorptive defect-induced damage was revealed. The damage characteristics of 532 nm polarizers and 1064 nm polarizers have been also compared. The mussel damage pits, which are similar to the typical damage morphologies of ultraviolet (UV) laser damage to fused silica, were observed for the first time in coatings of 532 nm polarizers. This suggests that, the polishing-induced subsurface damage of fused silica substrates may tend to be excited by a short-wavelength laser rather than the fundamental wavelength. • The damage resistance and damage characteristics of 532 nm polarizers in different laser damage test protocols, including 1-on-1, S-on-1, and Raster Scan, have been summarized, as a reference for thin-film optics in high-power laser applications. • The damage characteristics of 532 nm polarizers and 1064 nm polarizers were compared. The subsurface damage of fused silica substrates is easily excited by short-wavelength lasers. • Mussel pits, associated with the ultraviolet laser damage of fused silica, were observed in the coatings for the first time. [ABSTRACT FROM AUTHOR]

Abstract: The impact of two organic contamination modes of toluene on the damage characteristics of a high reflective film (HR) at 1064nm is investigated. The laser-induced damage modifications of HR films are locally analyzed by the Raman techniques, optical microscopy and scanning electron microscopy (SEM). It is found that liquid phase toluene decreases laser-induced damage threshold (LIDT) and gaseous phase toluene seems to be benign and increases the LIDT of the HR film. A possible damage mechanism is analyzed and discussed. [ABSTRACT FROM AUTHOR]

Abstract: The antimony doped tin oxide (SnO2:Sb) (ATO) thin films were prepared by oblique angle electron beam evaporation technique. X-ray diffraction, field emission scanning electron microscopy, UV–vis–NIR spectrophotometer and four-point probe resistor were employed to characterize the structure, morphology, optical and electrical properties. The results show that oblique angle deposition ATO thin films with tilted columns structure are anisotropic. The in-plane birefringence of optical anisotropy is up to 0.035 at α =70°, which means that it is suitable as wave plate and polarizer. The electrical anisotropy of sheet resistance shows that the sheet resistance parallel to the deposition plane is larger than that perpendicular to the deposition plane and it can be changed from 900Ω/□ to 3500Ω/□ for deposition angle from 40° to 85°, which means that the sheet resistance can be effectively tuned by changing the deposition angle. Additionally, the sandwich structure of SiO2 buffer layer plus normal ATO films and oblique angle deposition ATO films can reduce the resistance, which can balance the optical and electrical anisotropy. It is suggested that oblique angle deposition ATO thin films can be used as transparent conductive thin films in solar cell, anti-foggy windows and multifunctional carrier in liquid crystal display. [Copyright &y& Elsevier]

Abstract: Y2O3/SiO2 coatings were deposited on fused silica by electron beam evaporation. A continuous wave CO2 laser was used to condition parts of the prepared samples at different scanning speeds in the air. LAMBDA 900 spectrometer was used to investigate the changes of the transmittance and residual reflection spectrum. A Nomarski microscope under dark field was used to examine the changes of the micro defect density. The changes of the surface roughness and the microstructure of the film before and after conditioning were investigated by AFM and X-ray diffraction, respectively. We found that laser-induced damage threshold (LIDT) of the films conditioning at 30mm/s scanning speed was increased by more than a factor of 3 over the thresholds of the as-deposited films. The conditioning effect was correlated with an irradiation-induced decrease of the defect density and absorption of the films. [Copyright &y& Elsevier]

Abstract: Adhesion between the interface of pure silver thin film and three kinds of low refractive index coatings MgF2, Al2O3, SiO2 were compared in this article. The results indicated that the adhesion of Al2O3 and Ag was evidently superior to that of MgF2 and Ag, and the adhesion of MgF2 and Ag was evidently superior to that of SiO2 and Ag. Reasons were analyzed accordingly. On the other hand, we compared the effect on the optical characteristic of Ag film when these three kinds of films were used as protective coatings and enhanced coatings. Considering the difference of the adhesion between Ag and MgF2, Al2O3, SiO2, suited uses are given for each other. [Copyright &y& Elsevier]

The residual stress in ZrO2 thin films prepared by electron beam evaporation was measured by viewing the substrate deformation using an optical interferometer. The influences of deposition temperature and deposition rate on the residual stress have been studied. The results show that residual stress in ZrO2 thin films varies from tensile to compressive depending on deposition temperature and deposition rate, respectively. The value of compressive stress increases with the increasing of deposition temperature and deposition rate. At the same time, X-ray diffraction measurement was carried out in order to examine the crystallization behavior of the ZrO2 thin films as a function of deposition temperature and deposition rate. The relationship between the residual stress and the microstructure has also been discussed. [Copyright &y& Elsevier]

TiO2 films are deposited by electron beam evaporation as a function of oxygen partial pressure. The packing density, refractive index, and extinction coefficient all decrease with the increase of pressure, which also induces the change of the film’s microstructure, such as the increase of voids and H2O concentration in the film. The laser-induced damage threshold (LIDT) of the film increases monotonically with the rise of pressure in this experiment. The porous structure and low nonstoichiometric defects absorption contribute to the film’s high LIDT. The films prepared at the lowest and the highest pressure show nonstoichiometric and surface-defects-induced damage features, respectively. [ABSTRACT FROM AUTHOR]

WO 3 thin films fabricated by glancing angle deposition (GLAD) are proposed as excellent electrochromic coatings with favorable ion diffusion. A ∼ 500-nm film prepared by GLAD had a relatively large transmittance modulation. The crystallization structure, surface morphology, chemical state, optical and electrochromic properties of WO 3 thin films were systematically characterized upon annealing treatment. Compared with annealed WO 3 porous nanostructured films, the amorphous as-deposited films exhibited a high coloration efficiency and stable reversibility. Furthermore, the GLAD WO 3 films exhibit the tunable angular selectivity under illumination with p-polarized light because of the birefringence, which could extend the application range of nanostructured films in the electrochromic field. [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]

Damage behavior of HfO 2 and SiO 2 films under subpicosecond irradiation is investigated experimentally and theoretically in this work. The typical damage phenomenon is the transition from isolated submicrometer pits to integral ablation at transitive threshold. The experimental damage thresholds for both coatings are consistent with the theoretical calculation. The rate equation considering the feedback effect of electron number density is applied to calculate the deposited energy density, which illustrates the evolution of damage morphology. [ABSTRACT FROM AUTHOR]

The present work reports the nonlinear optical susceptibility of nanocrystalline ZnSe thin films with different thicknesses, measured using third-order harmonic technology at irradiation wavelengths λ of 1200–1900 nm. The results show that the third-order nonlinear susceptibility χ(3) of ZnSe thin films is a function of the pump wavelength and film thickness. The χ(3) values for the thinner 202-nm film generally decreased with the redshift of the wavelength and were approximately 10−20 m2/V2 at λ ≤ 1500 nm and 10−21 m2/V2 at λ > 1500 nm. The χ(3) values for the thicker 1021-nm film did not follow a decreasing trend, but instead exhibited local peaks at 1350, 1500 and 1750 nm, with a maximum value of approximately 2.4 × 10−19 m2/V2 at λ = 1750 nm. Within 1200–1900 nm, the χ(3) of the thicker film was always greater than that of the thinner film. In addition, a weak second-order harmonic at wavelengths within 1100–1300 nm was observed for the 1021 nm ZnSe thin film. The large difference in the nonlinear optical properties between the thinner and thicker film samples is conjectured to be caused by the increased density of geometric defects and the gradual formation of local anisotropy with increasing film thickness. Nonlinear optical coefficient measurements of ZnSe thin films with different thicknesses over a broad spectrum are important for the application of these films in nonlinear thin-film optoelectronic devices. • The third-order nonlinear susceptibility χ(3) of nanocrystalline ZnSe thin film is a function of irradiation wavelength and film thickness. • Within the spectra for 1200–1900 nm, χ(3) of the thinner 202-nm film generally decreased with the redshift of the wavelength. However, χ(3) of the thicker 1021-nm film exhibited local peaks at 1350, 1500 and 1750 nm. • The χ(3) values of the thicker film were generally greater than those of the thinner film. • An unexpected second-order harmonic was generated behind the thicker film at an incident wavelength of 1100–1300 nm. • The trends for increased density of geometric defects and gradual formation of local anisotropy with increasing film thickness were found. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO 2 ) nanostructured thin film (TNF), as an important semiconductor exhibiting large surface-to-volume ratio and unique property, has attracted more and more researches. As an important versatile nanofabrication technique, the glancing angle deposition technique (GLAD) is used to fabricate the TNF, frequently. However, little is known about the influence of GLAD on microstructure, crystalline structure, Ti/O chemical state and photoluminescence (PL) properties of TiO 2 thin films. In this paper, pure anatase TNF and traditional TiO 2 thin film (TTF) were deposited by combining GLAD system with the annealing treatment. All of the prepared TNFs keep discrete nanoscale columnar structures characterized by SEM. The evolution of morphology, crystallization structure, Ti/O chemical state and PL properties of TNFs and TTFs under annealing treatment have been investigated in detail. Simultaneously, comparing with TTFs, the influence of GLAD on TNFs material properties has been analyzed further. With the optimum annealing temperature (400 °C), one can obtain fine nanostructures and pure anatase precipitation of TNFs. The GLAD technique can adjust the preferred crystal orientation of TiO 2 thin films, which can be used as a method of material structural design. Both TNFs and TTFs exhibit broad band (380–700 nm) photoluminescence. Nevertheless, the TNFs exhibit much weaker and smoother PL spectra than that of TTFs, due to the large surface-to-volume ratio. The results indicate the potential good catalytic applications of TNFs deposited by GLAD. [ABSTRACT FROM AUTHOR]

Abstract: HfO2 films, using metal hafnium as starting material, are deposited by plasma-ion assisted electron evaporation with different Advanced Plasma Source (APS) bias voltages. The refractive index and extinction coefficient are calculated, the chemical state and composition, as well as the stress and aging behavior is investigated. Laser induced damage threshold (LIDT) and damage mechanism are also evaluated and discussed. Optical, structural, mechanical and laser induced damage properties of HfO2 films are found to be sensitive to APS bias voltage. The film stress can be tuned by varying the APS bias voltage. Damage morphologies indicate the LIDT of the HfO2 films at 1064nm and 532nm are dominated by the nodular-defect density in coatings, while the 355nm LIDT is dominated by the film absorption. HfO2 films with higher 1064nm LIDT than samples evaporated from hafnia are achieved with bias voltage of 100V. [Copyright &y& Elsevier]

Laser coatings designed for space applications not only encounter harsh space environments, but also suffer from laser irradiation. High-energy radiation in space, such as Gamma rays, can cause defects and other damage to materials, which could contribute to laser damage induced by defect absorption. In this work, we studied the optical properties and structural composition of three groups of 1064 nm multilayer antireflection (AR) coatings irradiated by Gamma rays (345 Gy), and the effect of Gamma ray radiation on the laser-induced damage properties of thin films. Experimental results revealed that after exposure to Gamma ray, the absorption and surface roughness of the AR coating increased while the transmittance decreased. X-ray photoelectron spectroscopy (XPS) analysis confirmed that SiO 2 is more fragile under Gamma radiation compared to Ta 2 O 5 and HfO 2. It was also demonstrated that the Gamma ray damage of AR coatings mainly occurred in the SiO 2 layers, and consist of generation of oxygen vacancies and charging defects. The defects generated by Gamma rays increased the absorption of the laser power by the film, hence increasing the probability of laser-induced damage and reducing the laser-induced damage threshold of the film. The coatings prepared by sputtering deposition technique showed lower probability of damage by Gamma ray radiation compared to electron-beam evaporated coatings. • The optical properties and structural composition of the 1064 nm AR coating after Gamma ray irradiation are studied. • The stability of different oxide materials prepared by different processes after Gamma irradiation is compared. • The damage of the film irradiated by Gamma rays under high-energy laser is studied. • This work provides an important reference for the development of space laser coatings. [ABSTRACT FROM AUTHOR]

In this paper, nanostructured ZrO films were prepared by electron beam evaporation with the glancing angle deposition (GLAD) technique. Columnar films with voids in between formed owing to the self-shadowing effect and the limited diffusion of deposited atoms. The microstructure evolves from slanted columnar structure to helical and pillar structures as the substrate rotational speed increases. The diameter of the columns is in the range of 30-50 nm. A higher rotational speed favors a larger nodule size and a greater surface roughness. Due to the porous structure, the refractive index n of GLAD ZrO films varies from 1.75 to 1.80, lower than that of bulk material. A maximum value of birefringence (Δ n=0.03) is obtained in a slanted columnar structure, and the relationship between birefringence and microstructure orientation is discussed. Our results demonstrate that glancing angle deposition is a feasible approach for designing the nanostructure and optical properties of thin films. [ABSTRACT FROM AUTHOR]

TiO2: 2%Sm3+ thin films were prepared by oblique angle deposition. X-ray diffraction (XRD), scanning electron microscope (SEM), UV-Vis-NIR spectrophotometer, fluorescence spectrophotometer was employed to characterize the structure and optical properties of TiO2: 2%Sm3+ thin films. The results indicated that these thin films were with anisotropic columnar structure before and after calcination. The optical anisotropy measured by transmission difference (Tp-Ts) at 500nm was increasing from 8% to 33% with calcination. Under ultraviolet excitation (λex = 330nm) and commercial 365nm UV lamp excitation, these TiO2: Sm3+ thin films show intense 4G5/2→ 6H5/2, 7/2, 9/2 emissions of Sm3+. The polarized photoluminescence was anticipated in the anisotropic thin films. [ABSTRACT FROM PUBLISHER]

Abstract: Polarizers respectively with broad polarizing region bandwidth, large layer thickness error tolerance and high extinction ratio are designed and prepared. Transmittance spectra of the prepared samples are measured at Brewster''s angle, and the results show that different requirements can be fulfilled by optimized designs. Spectral performance of designs with higher layer thickness error tolerance coincides better with the theoretical spectra. Laser induced damage threshold of the prepared samples are evaluated. Electric field distribution, defect, film absorption, and damage morphology are investigated, and the results indicate that electric field distribution in high index layers is the main reason that causes the difference of laser induced damage threshold. For both p polarized and s polarized light, the lower the electric field peak value and the farther the layer, which has the strongest electric field away from air, the higher the laser induced damage threshold. [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 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: 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: HfO2 is one of the most important high refractive index materials for depositing high power optical mirrors. In this research, HfO2 thin films were prepared by dual-ion beam reactive sputtering method, and the laser-induced damage thresholds (LIDT) of the sample were measured in 1-on-1 mode for laser with 1064nm wavelength. The results indicate that the LIDT of the as-grown sample is only 3.96J/cm2, but it is increased to 8.98J/cm2 after annealing under temperature of 200°C in atmosphere. By measuring the laser weak absorption and SIMS of the samples, we deduced that substoichiometer is the main reason for the low LIDT of the as-grown sample, and the experiment results were well explained with the theory of electronic-avalanche ionization. [Copyright &y& Elsevier]

Abstract: Nb2O5 sculptured thin films deposited by electron beam evaporation with glancing angle deposition were prepared. Nb2O5 sculptured thin films with tilted columns are optical anisotropy. XRD, SEM, UV–vis–NIR spectra are employed to characterize the microstructure and optical properties. The maximum of birefringence (Δn) is up to 0.045 at α =70° with packing density of 0.487. With increasing the deposition angle, refractive index and packing density of Nb2O5 STF are decreasing. The relationship among deposition parameter, microstructure and optical properties was investigated in detail. [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: 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: A series of Ta2O5 films with different SiO2 additional layers including overcoat, undercoat and interlayer was prepared by electron beam evaporation under the same deposition process. Absorption of samples was measured using the surface thermal lensing (STL) technique. The electric field distributions of the samples were theoretical predicted using thin film design software (TFCalc). The laser induced damage threshold (LIDT) was assessed using an Nd:YAG laser operating at 1064nm with a pulse length of 12ns. It was found that SiO2 additional layers resulted in a slight increase of the absorption, whereas they exerted little influence on the microdefects. The electric field distribution among the samples was unchanged by adding an SiO2 overcoat and undercoat, yet was changed by adding an interlayer. SiO2 undercoat. The interlayer improved the LIDT greatly, whereas the SiO2 overcoat had little effect on the LIDT. [Copyright &y& Elsevier]

Abstract: TiO2 thin films were prepared by electron beam evaporation at different oxygen partial pressures. The influences of oxygen partial pressure on optical, mechanical and structural properties of TiO2 thin films were studied. The results showed that with the increase of oxygen partial pressure, the optical transmittance gradually increased, the transmittance edge gradually shifted to short wavelength, and the corresponding refractive index decreased. The residual stresses of all samples were tensile, and the value increased as oxygen partial pressure increasing, which corresponded to the evolutions of the packing densities. The structures of TiO2 thin films all were amorphous because deposition particles did not possess enough energy to crystallize. [Copyright &y& Elsevier]

Abstract: ZrO2 thin films were prepared by electron beam evaporation at different oxygen partial pressures. The influences of oxygen partial pressure on structure and related properties of ZrO2 thin films were studied. Transmittance, thermal absorption, structure and residual stress of ZrO2 thin films were measured by spectrophotometer, surface thermal lensing technique (STL), X-ray diffraction and optical interferometer, respectively. The results showed that the structure and related properties varied progressively with the increase of oxygen partial pressure. The refractive indices and the packing densities of the thin films decreased when the oxygen partial pressure increased. The tetragonal phase fraction in the thin films decreased gradually as oxygen partial pressure increased. The residual stress of film deposited at base pressure was high compressive stress, the value decreased with the increase of oxygen partial pressure, and the residual stress became tensile with the further increase of oxygen pressure, which was corresponding to the evolution of packing densities and variation of interplanar distances. [Copyright &y& Elsevier]

Abstract: Thin films of ZrO2, HfO2 and TiO2 were deposited on kinds of substrates by electron beam evaporation (EB), ion assisted deposition (IAD) and dual ion beam sputtering (DIBS). Then some of them were annealed at different temperatures. X-ray diffraction (XRD) was applied to determine the crystalline phase and the grain size of these films, and the results revealed that their microstructures strongly depended on the deposition conditions such as substrate, deposition temperature, deposition method and annealing temperature. Theory of crystal growth and migratory diffusion were applied to explain the difference of crystalline structures between these thin films deposited and treated under various conditions. [Copyright &y& Elsevier]

Abstract: A series of silver films with different thickness were prepared under identical conditions by direct current magnetron sputtering. The optical properties of the silver films were measured using spectrophotometric techniques and the optical constants were calculated from reflection and transmission measurements made at near normal incidence. The results show that the optical properties and constants are affected by films'' thickness. Below the critical thickness of 17 nm at which Ag film forms a continuous film, the optical properties and constants vary significantly as the thickness of films increases and then tends to a stable value which is reached at 41 nm. X-ray diffraction measurements were carried out to examine the structure and stress evolution of the Ag films as a function of films'' thickness. It was found that the interplanar distance of (111) orientation decreases when the film thickness increases and tends to be close to that of bulk material. The compressive strains also decrease with increasing thickness. [Copyright &y& Elsevier]

Abstract: TiO2 films deposited by electron beam evaporation with glancing angle deposition (GLAD) technique were reported. The influence of flux angle on the surface morphology and the microstructure was investigated by scanning electron microscopy. The GLAD TiO2 films are anisotropy with highly orientated nanostructure of the slanted columns. With the increase of flux angle, refractive index and packing density decrease. This is caused by the shadowing effect dominating film growth. The anisotropic structure of TiO2 films results in optical birefringence, which reaches its maximum at the flux angle α =65°. The maximum birefringence of GLAD TiO2 films is higher than that of common bulk materials. It is suggested that glancing angle deposition may offer an effective method to obtain tailorable refractive index and birefringence in a large continuous range. [Copyright &y& Elsevier]

Abstract: ZrO2 films were prepared by electron beam evaporation with glancing angle deposition (GLAD) technique. The as-deposition and annealed ZrO2 films are all amorphous, different from that deposited at normal incidence. Due to the shadowing effect, a highly orientated structure composed of slanted columns formed, and the obtained films became the mixture of slanted columns and voids. The relationship among the effective refractive index, packing density and flux incident angle was investigated. The refractive index and packing density of ZrO2 films decrease with the increase of the incident angle. The in-plane birefringence of GLAD ZrO2 films was calculated. At the packing density of 0.576, the maximum birefringence is 0.037. [Copyright &y& Elsevier]

Abstract: Thin-film design used to fabricate multi-layer dielectric (MLD) gratings should provide high transmittance during holography exposure, high reflectance at use wavelength and sufficient manufacturing latitude of the grating design making the MLD grating achieve both high diffraction efficiency and low electric field enhancement. Based on a (HLL)9H design comprising of quarter-waves of high-index material and half-waves of low-index material, we obtain an optimum MLD coating meeting these requirements by inserting a matching layer being half a quarter-wave of Al2O3 between the initial design and an optimized HfO2 top layer. The optimized MLD coatings exhibits a low reflectance of 0.017% under photoresist at the exposure angle of 17.8° for 413nm light and a high reflectance of 99.61% under air at the use angle of 51.2° for 1053nm light. Numerical calculation of intensity distribution in the photoresist coated on the MLD film during exposure shows that standing-wave patterns are greatly minimized and thus simulation profile of photoresist gratings after development demonstrates smoother shapes with lower roughness. Furthermore, a MLD gratings with grooves etched into the top layer of this MLD coating provides a high diffraction efficiency of 99.5% and a low electric field enhancement ratio of 1.53. This thin-film design shows perfect performances and can be easily fabricated by e-beam evaporation. [Copyright &y& Elsevier]

Abstract: Negative ion element impurities breakdown model in HfO2 thin film was reported in this paper. The content of negative ion elements were detected by glow discharge mass spectrum analysis (GDMS); HfO2 thin films were deposited by the electron-beam evaporation method. The weak absorption and laser induced damage threshold (LIDT) of HfO2 thin films were measured to testify the negative ion element impurity breakdown model. It was found that the LIDT would decrease and the absorption would increase with increasing the content of negative ion element. These results indicated that negative ion elements were harmful impurities and would speed up the damage of thin film. [Copyright &y& Elsevier]

Abstract: Multi-layer dielectric (MLD) gratings for pulse compressors in high-energy laser systems should provide high diffraction efficiency as well as high laser induced damage thresholds (LIDT). Nonuniform optical near-field distribution is one of the important factors to limit their damage resistant capabilities. Electric field distributions in the gratings and multi-layer film region are analyzed by using Fourier modal method. Optimization of peak electric field in the gratings ridge is performed with a merit function, including both diffraction efficiency and electric field enhancement when the top layer material is HfO2 and SiO2, respectively. A set of optimized gratings parameters is obtained for each structure, which reduce the peak electric field within the gratings ridge to being respective 1.39 and 1.84 times the value of incident light respectively. Finally, we also discuss the effects of gratings refractive index, gratings sidewall angle and incident angle on peak electric field in the gratings ridge. [Copyright &y& Elsevier]

Abstract: The glancing angle deposition (GLAD) technique was used to deposit ZnS films by electron beam evaporation method. The cross sectional scanning electron microscopy (SEM) image illustrated a highly orientated microstructure composed of slanted column. The atomic force microscopy (AFM) analysis indicated that incident flux angle had significant effects on the nodule size and surface roughness. Under identical nominal thickness, the actual thickness of the GLAD films is related to the incident flux angle. The refractive index and in-plane birefringence of the GLAD ZnS films were discussed, and the maximum birefringence Δn =0.036 was obtained at incident flux angle of α =80°. Therefore, the glancing angle deposition technique is a promising way to create a columnar structure with enhanced birefringent property. [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: A model for refractive index of stratified dielectric substrate was put forward according to theories of inhomogeneous coatings. The substrate was divided into surface layer, subsurface layer and bulk layer along the normal direction of its surface. Both the surface layer (separated into N 1 sublayers of uniform thickness) and subsurface layer (separated into N 2 sublayers of uniform thickness), whose refractive indices have different statistical distributions, are equivalent to inhomogeneous coatings, respectively. And theoretical deduction was carried out by employing characteristic matrix method of optical coatings. An example of mathematical calculation for optical properties of dielectric coatings had been presented. The computing results indicate that substrate subsurface defects can bring about additional bulk scattering and change propagation characteristic in thin film and substrate. Therefore, reflectance, reflective phase shift and phase difference of an assembly of coatings and substrate deviate from ideal conditions. The model will provide some beneficial theory directions for improving optical properties of dielectric coatings via substrate surface modification. [Copyright &y& Elsevier]

Abstract: A series of HR coatings, with and without overcoat, were prepared by electron beam evaporation using the same deposition process. The laser-induced damage threshold (LIDT) was measured by a 355nm Nd:YAG laser with a pulse width of 8ns. Damage morphologies of samples were observed by Leica-DMRXE Microscope. The stress was measured by viewing the substrate deformation before and after coatings deposition using an optical interferometer. Reflectance of the samples was measured by Lambda 900 Spectrometer. The theoretical results of electric field distributions of the samples were calculate by thin film design software (TFCalc). It was found that SiO2 overcoat had improved the LIDT greatly, while MgF2 overcoat had little effect on the LIDT because of its high stress in the HR coatings. The damage morphologies were different among HR coatings with and without overcoats. [Copyright &y& Elsevier]

Abstract: Used in chirped-pulse amplification system and based on multi-layer thin film stack, pulse compressor gratings (PCG) are etched by ion-beam and holographic techniques. Diffraction efficiency and laser-induced damage threshold rely on the structural parameters of gratings. On the other hand, they depend greatly on the design of multi-layer. A theoretic design is given for dielectric multi-layer, which is exposed at 413.1nm and used at 1053nm. The influences of coating design on optical characters are described in detail. The analysis shows that a coating stack of H3L (H2L)∧9H0.5L2.01H meets the specifications of PCG well. And there is good agreement of transmission between experimental and the theoretic design. [Copyright &y& Elsevier]

Abstract: CO2 laser irradiation experiments on ZnO thin films are reported. The structural, optical, luminescent and vibrational properties of the samples were investigated by X-ray diffraction (XRD), transmittance, photoluminescence (PL) and Raman measurements. XRD results show that the crystalline of the irradiated films was improved. The (002) peaks of irradiated ZnO films shift to higher 2θ angles due to the stress relaxation in the case of laser beam irradiation. From optical transmittance spectra, all films exhibit high transmittance in the visible range, the optical band edge of irradiated films showed a redshift compared with that of as-grown films. Compared with the as-grown films, the photoluminescence emission (in particular the relative intensities of visible emissions) intensities of irradiated samples enhanced. In the Raman scattering spectra, both the A1 and E2 modes exhibited slight Raman blueshift. [Copyright &y& Elsevier]

Abstract: The origin, character, analysis and treatment of subsurface damage (SSD) were summarized in this paper. SSD, which was introduced to substrates by manufacture processes, may bring about the decrease of laser-induced damage threshold (LIDT) of substrates and thin films. Nondestructive evaluation (NDE) methods for the measurement of SSD were used extensively because of their conveniences and reliabilities. The principle, experimental setup and some other technological details were given for total internal reflection microscopy (TIRM), high-frequency scanning acoustic microscopy (HFSAM) and laser-modulated scattering (LMS). However, the spatial resolution, probing depth and theoretic models of these NDE methods demanded further studies. Furthermore, effective surface treatments for minimizing or eliminating SSD were also presented in this paper. Both advantages and disadvantages of ion beam etching (IBE) and magnetorheological finishing (MRF) were discussed. Finally, the key problems and research directions of SSD were summarized. [Copyright &y& Elsevier]

Abstract: Laser conditioning effects of the HfO2/SiO2 antireflective (AR) coatings at 1064nm and the accumulation effects of multi-shot laser radiation were investigated. The HfO2/SiO2 AR coatings were prepared by E-beam evaporation (EBE). The single-shot and multi-shot laser induced damage threshold was detected following ISO standard 11254-1.2, and the laser conditioning was conducted by three-step raster scanning method. It was found that the single-shot LIDT and multi-shot LIDT was almost the same. The damage mostly >80% occurred in the first shot under multi-shot laser radiation, and after that the damage occurring probability plummeted to <5%. There was no obvious enhancement of the laser damage resistance for both the single-shot and multi-shot laser radiation of the AR coatings after laser conditioning. A Nomarski microscope was employed to map the damage morphology, and it found that the damage behavior is defect-initiated for both unconditioned and conditioned samples. [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]

Laser conditioning effects of the dielectric 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 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. During the sub-threshold fluence raster scanning, the minor damage about defects size was found and the assumption of pre-damage mechanism, based on the functional damage concept, was put forward. The improvement of the laser induced damage threshold (LIDT) was attributed to the benign damage of the defects and the dependence on the coating design owed to the damage growth behavior of different coating designs. [Copyright &y& Elsevier]