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The ever-increasing demand for broadband antireflection (AR) coatings has led to a growing interest in nanolaminates (NLs) with tunable properties. However, achieving excellent optical performance in NLs can be challenging due to multiple interfaces and a rather thin sublayer. In this study, we systematically investigated the factor that deteriorates the optical performance, focusing on the sublayer thickness deviation, sublayer n deviation, and interfacial diffusion, to correct the n -profiles of NLs. A pre-correction strategy for the AR coating design is proposed and experimentally demonstrated via plasma-enhanced atomic layer deposition. The excellent fit of the spectrum demonstrates that the proposed design strategy can benefit structure-sensitive NL-based coatings. [Display omitted] • The factor that deteriorates the optical performance of nanolaminate-based broadband AR coatings has been systematically investigated. • Depending on the relative magnitudes of the interfacial diffusion and sublayer thicknesses, plasma-enhanced atomic-layer-deposited HfO 2 –SiO 2 nanolaminates were categorized into three typical types. • A pre-correction strategy considering the sublayer thickness deviation, sublayer refractive index (n) deviation, and interfacial diffusion, to correct the n -profiles of nanolaminates was proposed and experimentally demonstrated via plasma-enhanced atomic layer deposition. • The broadband AR coating with pre-correction exhibits excellent agreement between the designed and measured spectra, with a root-mean-square error of <0.100, well below that without any pre-correction. • The significant improvement in the fitness of the spectra and coating-layer thickness between the design and experimentally measurement demonstrates that the proposed pre-correction design strategy can benefit other nanolaminate-based coatings whose spectral performance is sensitive to the coating structure. [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]

Liquid crystal polarization gratings (LCPGs) possess unique optical properties and therefore are widely used in laser systems. Therefore, developing our understanding of the laser damage resistance of LCPGs is critical for future high-intensity laser applications. In this study, the LCPGs (Λ = 8 μm) were fabricated from liquid crystal polymer (LCP) films with photo-alignment technology, which had a small-angle (∼7.51°) diffraction order with high diffraction efficiency (∼92 %) under chiral polarized incidence at 1064 nm. The diffraction efficiency and polarization of each diffraction order were determined by the polarization of the incident light. The damage characteristics of the LCPGs were investigated using a chiral polarized nanosecond laser at 1064 nm in a one-on-one test. The laser-induced damage thresholds (LIDTs) of left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) were 8.0 J/cm2 and 8.5 J/cm2, respectively. For comparison, the LIDTs of S-polarization and P-polarization were 7.8 J/cm2 and 8.4 J/cm2, respectively. All the damage occurred at the interface between the LCP layer and the substrate when the laser fluence was near the LIDT, and the damage morphology was observed with a scanning electron microscope (SEM), including flat pits, cracks, and bumps at the edge of the pits. The results indicate that the LIDTs and damage morphology of the LCPGs were insensitive to the polarization of the irradiation. The electrical effects of differently polarized irradiation on the LCPGs were simulated using the finite element method (FEM). The electric field distribution was symmetrical under irradiation by LHCP and RHCP lasers. However, the distribution of the electric field under different linearly polarized irradiation conditions were distinct. Based on these findings, we believe that the contribution of chiral polarized irradiation to the damage was consistent and that the LIDTs were similar. This study has important implications for the application and development of LCPGs in high-intensity laser systems. • The laser-induced damage of liquid crystal polarization gratings (LCPGs) is first proposed. • We investigated the laser-induced damage of the LCPGs using a nanosecond pulsed laser with chiral polarized irradiation. • This study provides reference for the application and development of LCPGs in high-intensity laser systems. [ABSTRACT FROM AUTHOR]

The broadband optical parametric chirped-pulse amplification scheme is considered as a promising approach for developing the 100 PW or even exawatt laser facilities. Based on a quarter-wavelength optical-thickness mirror with a reverse-chirped structure, a Nb 2 O 5 /SiO 2 low-dispersion mirror (LDM) and a Nb 2 O 5 –Al 2 O 3 /SiO 2 composite LDM (CLDM) for a 910 (±100 nm) laser system are designed and experimentally evaluated. The laser damage properties of the mirrors were investigated in an uncompressed nanosecond laser pulse with a spectrum bandwidth of 200 nm for the first time. From the aspects of both broad-spectrum electric field and thermal stress, the damage behavior is elucidated. The results show that the protective layer has both positive and negative effects in the broad spectrum and the competing results of the two effects determine whether the protective layer can play a protective role. Damage morphology and thermal stress calculations show that the laser introduced thermal stress mismatch will lead to the peeling damage of CLDM. This study shows that broad-spectrum optics should be designed and fabricated by considering the electric field of all spectrum components and thermodynamic properties of layer materials; this provides insight into the development of high-performance broad-spectrum optics. • Low-dispersion mirrors with a bandwidths of more than 200 nm have been designed without electric field enhancement. • The laser damage properties of the mirrors are investigated by using a nanosecond laser pulse with a spectrum bandwidth of 200 nm. • The mismatch of thermodynamic parameters between materials is the reason limiting the damage threshold. [ABSTRACT FROM AUTHOR]

With the development of the high power laser facilities, laser resistance of pulse compression grating is getting increased attention. The metal dielectric mixed grating (MDMG) is widely studied, because it has wide diffraction bandwidth, low surface stress and potential high threshold. The effect of nodular defect size on damage of MDMG is studied by experiments and theoretical analysis in two typical cases. The initial damages appear in the district of nodular defect due to local electric field enhancement induced by nodular defect, which is different with the initial damage located in grating pillar of the perfect MDMG. Laser induced ionization theory is introduced to describe the damage process and give a quantitative analysis on the relationship of laser damage and nodular defect size. It is concluded that local electric field enhancement in nodular defect area would cause the electron density to reach the critical value and lead to the damage occurrence, and nodule damage critical diameters are 1400 nm and 1500 nm respectively in case 1 (seed under the grating pillar) and case 2 (seed under the grating groove) which will lead to nodule damage initiation. • The initial damages appear in the district of nodular defect which is different with the initial damage of perfect MDMG. • The nodule damage reason is that electron density reaches to critical value owing to local electric field enhancement. • Nodule damage critical diameter are 1400nm and 1500nm in case 1 and case 2 (seed under grating pillar and grating groove). [ABSTRACT FROM AUTHOR]

Antireflection (AR) coatings are deposited on UV grade fused silica substrates, which are cleaned in the dual ion beam sputtering device. Compared to ultrasonic and acid etching cleaning progress, ion beam etching improves the laser-induced damage threshold (LIDT) of substrates and AR coatings significantly at 355 nm. Ion beam etching declines the low LIDT defects drastically and removes lots of the impurity elements (Ce, Fe, K, and Na). Roughness test shows that the AR coatings and substrates with ion beam etching are very flat and of low roughness. Ion beam etching reduces the density of deep defect from substrates greatly. Damage morphologies show double layers delamination, which is explained via calculation of layer stress. This study will be helpful for preparation of high LIDT optical coatings. • The LIDT of the 355 nm AR coatings and substrates are improved greatly with ion beam etching of substrates. • The damage curves show that ion beam etching declined the low LIDT defects drastically. • The impurity elements (Ce, Fe, K, and Na) are removed efficiently, and the surfaces are quite smooth. • Damage morphologies show two different defects in AR coatings and correspond to the laser damage curves. • Laser damage mechanism of AR coatings is explained. [ABSTRACT FROM AUTHOR]

Abstract Laser-induced damage of ultraviolet (UV) coatings poses a great challenge and restricts its application in space. Coatings prepared by ion beam sputtering are dense and possess high laser-induced damage threshold (LIDT), which are absence of structural nodule defects. Subsurface damage defects easily exposed by etching are inevitable under substrate grinding and polishing processes, which are usually ignored in electron-beam evaporation coatings. In our experiments, we find that LIDT of 355-nm high-reflection (HR) coatings sputtered on etched substrates declines dramatically, meanwhile defect density increases. Pits are found on the surface of the substrates and the coatings, and the pits that induce laser damage are very small (submicron-scale). Laser damage morphologies reveal that damage sites are prone to occur around the pits caused by acid etching. Finite element analysis shows consistent results, enhancement of electric field and rise of temperature are obvious, and the most significant part is around the pits, which is prone to induce damage. To conclude, small structural defects are sensitive to laser-induced damage of HR coatings prepared by dual ion beam sputtering (DIBS). This work contributes to finding new ways of improving the LIDT of sputtering coatings. Highlights • The structural defects on substrates are relatively small and shallow, the depth and the diameter of the pits are in the range of ∼50–120 nm and ∼400–600 nm, respectively. • The diameters of the pits on the surface of the coatings (DIBS) are larger than the substrate, which is different from the EBE coatings and indicates different growth process. • The LIDTs of our samples are sharply declined by the presence of the pits, the damage morphologies show thermal ablation. • High electric field and temperature by a FEA method are found at the edge of the pits on the surface of the coatings, which agrees with the experimental result. • The pits strongly enhance the thermal effect, which increases the possibility of damage of 355 nm IBS coatings. [ABSTRACT FROM AUTHOR]

Abstract A comparative study of anti-reflection microstructures (ARMs) and ARMs with Al 2 O 3 coatings (Al 2 O 3 /ARMs) on zinc selenide (ZnSe) has been carried out. The transmittance and electric field intensities were analyzed and presented using finite-difference time-domain (FDTD) simulations. ARMs were successfully fabricated on ZnSe surfaces by reactive ion etching and an Al 2 O 3 layer was deposited onto the ARMs by an ion beam sputtering method. The theoretical analysis and experimental results showed that the transmittance of Al 2 O 3 /ARMs-treated ZnSe had a close relationship with the thickness of Al 2 O 3 layer and was higher than that of ARMs-treated ZnSe in the 2–5 μm wavelength range, which was due to the fact that the Al 2 O 3 /ARMs had a better graded refractive index profile. The angle-dependent reflectance of ZnSe with Al 2 O 3 /ARMs was lower than that with ARMs. A difference of the spatial distribution of the electric field intensity between ARMs and Al 2 O 3 /ARMs was observed due to the surface Al 2 O 3 coating, which predicted qualitative laser damage thresholds for both structures. The results of this study provide potential applications in high-efficiency IR optoelectronic devices and high power mid-infrared laser systems. Highlights • The transmittance of Al 2 O 3 /ARMs on ZnSe is enhanced by the more graded refractive index profile. • The composite antireflective structures allowed a significant improvement in omni-directional antireflective properties. • A change of the spatial distribution of the electric field intensity between ARMs and Al 2 O 3 /ARMs is observed. [ABSTRACT FROM AUTHOR]

The bandwidth and laser induced damage threshold (LIDT) are the key factors influencing the performance of broadband antireflection (AR) films in optical systems. In this study, we used glancing angle deposition (GLAD) technology to prepare an "interface free" ultrabroadband AR film with continuously varying refractive index and a nanorod structure. Owing to the changing refractive index from substrate to air, the average residual reflectivity of our AR films in the transmission band of 200–2500 nm of the entire fused quartz substrate is less than 0.55%, which is far superior to the traditional broadband AR film. Further, owing to removal of the interface and nanorod structure, the LIDTs of the ultrabroadband AR film at 1064 and 532 nm are 22.5 and 22.6 J/cm2, respectively. These are approximately 50% and 20% higher than those of the traditional 532 and 1064 nm AR film, respectively, indicating superior laser damage resistance. [Display omitted] • Ultrabroadband AR film design is proposed with continuous varying refractive index. • The interior of the film presents an"interface free" state and nanorods structure. • The average residual reflectivity of AR film is less than 0.55% in the 200–2500 nm. • The AR film exhibited superior laser damage resistance than traditional AR films. [ABSTRACT FROM AUTHOR]

In this work, gold films on two different types of substrates were fabricated by electron beam (e-beam) evaporation, and the femtosecond laser-induced damage properties were evaluated. The first sample was gold film deposited on fused silica, whereas the second was gold deposited on photoresist. 1-on-1 damage tests were implemented by an 800 ± 30 nm laser with pulse duration of 30 fs. Different damage thresholds and morphologies were obtained for the two samples. The damage threshold of the gold film on fused silica was 0.64 J/cm 2 , with the typical damage morphology of thermal ablation and melting; the damage threshold of the gold film on photoresist was 0.30 J/cm 2 , with the typical damage morphology of blisters or peeling off. In order to better understand the impact of the substrate on the properties of the whole sample, the normalized electric field intensity, temperature, and thermal stress distributions were calculated. The adhesion between the gold film and substrate were measured and the experimental results well agreed with the theoretical analysis. The results indicate that gold films deposited onto grating-structured fused silica will have more powerful laser damage resistance performance. [ABSTRACT FROM AUTHOR]

Au-coated gratings (ACGs) for chirped pulse compression were irradiated using 800 ± 35 nm multiple laser pulses with duration of 30 fs. The laser-induced damage threshold (LIDT) of Au-coated gratings decreases from 0.35 J/cm 2 to 0.10 J/cm 2 with the increased pulse shots. The near threshold damage feature of Au-coated gratings at different pulses shows blisters. It is indicated that the gradually increased blister height with increasing multiple pulses on ACGs is caused by the accumulation effect. The damage morphologies combine with simulated results indicate that the damage of the ACGs can be attributed to the pinholes at the base of grating pillars and the separation of gold coating and photoresist gratings caused by the photoresist absorbed the incident laser energy. Therefore, we consider the damage threshold can be enhanced by optimizing coating deposition technology to reduce pinholes density and increase the adhesion between the gold and the photoresist. [ABSTRACT FROM AUTHOR]

Optical thin films with ultralow absorption loss are crucial for high-precision optical systems. The ionic oxygen concentration and oxygen flow rate play decisive roles in the absorption loss of the film. We prepared SiO 2 and Ta 2 O 5 monolayers using a double-ion beam sputtering (DIBS) deposition system and studied the effects of different ionic oxygen concentrations and oxygen flow rates on the optical constants, weak absorption, –OH defects, and dispersion energy parameters. The results show that the oxygen flow slightly affects the weak absorption of SiO 2 films, while a higher ionic oxygen concentration facilitates the reduction of the absorption loss of SiO 2 films, resulting in fewer –OH defects. A higher ionic oxygen concentration decreases the refractive index of the Ta 2 O 5 films. The relatively low lattice permittivity of the Ta 2 O 5 films may be attributed to the argon bubbles wrapped in the film. Annealing can reduce the absorption of the film but cannot improve its surface roughness. A Ta 2 O 5 /SiO 2 high-reflection film was produced with an optimal ionic oxygen concentration and oxygen flow rate, with the lowest absorption loss for both materials. The weak absorption attained 1.4 ppm, playing a significant role in improving the performance of the high-power and high-precision optical systems. • The effects of ionic oxygen concentrations and oxygen flow on optical constants and absorption of thin films are studied. • The relative content of –OH in SiO 2 film with different ionic oxygen concentrations is calculated by the binding energy. • This work provides an important reference for the preparation of low-absorption-loss laser thin films. [ABSTRACT FROM AUTHOR]

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]

Served as electro-optic switch, frequency converter and the optical parametric chirped pulse amplifier (OPCPA), highly deuterated DKDP crystals are critical optical elements in high power laser systems. In our work, samples taken in Z direction and Ⅰ-type phase-match direction from an as-grown high deuterium DKDP crystal, which was grown by the rapid growth method with continuous filtration. Thermo-gravimetric apparatus (TGA) measurement was applied to obtain the deuterium content of the DKDP crystal. the results showed the deuterium level of the samples in our experiments exceeded 98%. The ultraviolet–visible–near-infrared transmittance spectrum showed that the transmittance of Z-cut at 532 nm and Ⅰ-type at 1064 nm were 92.99% and 96.07%, respectively. The 0% laser-induced damage threshold of Z-cut in 1064 nm was about 40J/cm2, exceeding much more than the application requirement in certain high power laser systems. The polarization state of laser had little effect on the laser-induced damage characteristics of Ⅰ-type sample. Then the laser-induced damage morphologies of 98% DKDP crystals induced by the 1064 nm and 532 nm lasers were investigated. The results indicated that the "micro-explosion" of different kinds of defects in the bulk led to different damage morphologies, and many cracks in the damage pinpoints presented the regular orientation with better consistency in view of the Ⅰ-type phase-match direction. Our research can provide a reference for the applications of highly deuterated DKDP crystals in high power laser systems. • The deuterium level of the DKDP crystals in Z and Ⅰ-type phase-match direction in the work exceeded 98%. • The 0% LIDT of Z-cut DKDP in 1064 nm and Ⅰ-type DKDP were about 40J/cm2 and over 20J/cm2, respectively. • Cracks in the damage pinpoints presented the orientation with better consistency along regular chemical bond distribution. [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]

Liquid crystal devices (LCDs) are widely used in several applications involving high-power lasers, such as laser processing, laser shaping, laser communication, laser radar and so on. Investigation on the performance of the LCDs working in high-power laser has always been of concern. In this study, a modified nearly common-path interferometry technique is proposed to investigate the phase modulation characteristics of the LCD irradiated by 1064 nm continuous-wave (CW) laser with Gaussian beam profile and an effective area of 0.1 cm2. In addition, the temperature rise of the LCD induced by laser irradiation was synchronously measured with an infrared thermal imager. A quantitative and dynamic investigation of the relation between the thermal effect caused by the laser and the phase-modulation variation is reported. Experimental results showed that the trend of temperature increase of the LCD was similar to that of phase shift variation. The theoretical phase shift calculated using the temperature-dependent LC refractive index coincided with the experimental results. This indicated that the refractive index change induced by temperature was the main reason for the phase-modulation variation of the LCD under laser irradiation. When the laser power was further increased, interference fringe distortion appeared, and morphological changes in the LC were observed. This implied that the laser-induced temperature rise had reached the clearing point of the LC and that the LCD was inactive. The temperature simulation along the laser incidence direction implied that, under the irradiation CW laser, indium tin oxide (ITO) layer absorbs laser energy, resulting in a temperature rise and a small temperature gradient between the ITO, polyimide (PI) and LC layers. The rising temperature is too low to induced damage of ITO layer and PI layer, but influences the refractive index of the LC. Compared with other layers of the LCD, the LC material will fail first when the irradiated laser power is further risen. The transmission variation of an LCD induced by laser irradiation was found. Possibly owing to the refractive index change of the LC as well as the multilayer film structure of the LCD, there seemed to be a cyclical transmission variation. • In our study, a modified nearly common-path interferometry technique was proposed to investigate the phase modulation characteristics of the LCD under continuous-wave (CW) laser irradiation. • A quantitative and dynamic investigation of the relation between the thermal effect caused by the laser and the phase-modulation change was reported. • This indicated that the refractive index change induced by temperature was the main reason for the phase-modulation variation of the LCD under laser irradiation. • The temperature simulation along the laser incidence direction implied that, under the irradiation CW laser, ITO layer absorbed laser energy, resulting in a temperature rise and a small temperature gradient between the ITO, PI and LC layers. • Besides, the transmission variation of the LCD without polarizer induced by laser irradiation was first reported. [ABSTRACT FROM AUTHOR]

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]

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]

The high optical performance and laser-induced damage threshold (LIDT) of broadband hafnium oxide/silica (HfO 2 /SiO 2) dichroic coatings with high transmittance and reflectance around 532 and 1064 nm, respectively, are essential for the efficiency of a harmonic separation system. However, the transmittance of dichroic coatings tends to drop rapidly at 532 nm because of the half-wave hole effect. Moreover, an intense electric field penetrates the coating (~6 μm thick) to the substrate, thereby generating a challenge to improve the LIDT at 532 nm. In this paper, we study the methods to improve the optical performance and LIDT of HfO 2 /SiO 2 dichroic coatings prepared by electron-beam evaporation. The inhomogeneity in the growth characteristics of the HfO 2 layer is studied and considered in the design of dichroic coatings, which can improve spectral performance, especially by broadening the transmittance bandwidth around 532 nm. Additionally, the effects of the different treatment procedures, including ultrasonic cleaning, acid-solution etching, and argon-ion-beam etching, of the fused silica substrate on the LIDT of dichroic coatings are investigated by the raster-scan damage test method. We observe that the LIDT of dichroic coatings at 532 nm is limited by the surface and subsurface defects of the substrate. Etching ~200 nm of the surface of the fused silica substrate can effectively inhibit the occurrence of low-energy catastrophic growth damage. Compared with acid-solution etching, argon-ion-beam etching can yield improved substrate surface quality and increased LIDTs of dichroic coatings at 532 nm. • The refractive index inhomogeneity of the HfO 2 single layer is consistent with that of the HfO 2 layer in dichroic coatings. • HfO 2 /SiO 2 dichroic coatings considering the refractive-index inhomogeneity of HfO 2 layer inhibit the half-wave hole effect. • Laser damage at 532 nm mainly originates from the substrate subsurface defects in the redeposition (Beilby) layer. • Argon-ion-beam etching can bring better substrate surface quality and higher LIDTs of dichroic coatings at 532 nm. [ABSTRACT FROM AUTHOR]

An investigation of the impact of solvent content on polymerization feature size in multi-photon polymerization is presented. The negative tone, epoxy photoresist SU-8 is employed, and variety pre-baking time is set to obtain different solvent content. A convenient method, exposure under long-focal length and single pulse, is suggested to evaluate the impact of solvent. By measuring the polymer size under microscope, it shows that the polymerized diameters are reduced by ~40% due to only 4% loss of the solvent content. The inhibition of the mobility of photon-induced H+ cations due to the less solvent is considered to be responsible for the refinement of polymer feature size. It is because that the mobility of photon-induced H+ cation from high to low concentration area is restricted by reducing the solvent. The adjusting solvent content shows its potential to refine the feature size of MPP without influencing the degree of polymerization. • Vaporizing the solvent content could refine the feature size of MPP in SU-8 2075 photoresist. • A long focal-length and single pulse exposure was proposed to realize the exposure of multi-photon polymerization. • Feature sizes of the polymerization were evaluated by the microscope at the micro-scale. • Polymer diameters were reduced by ~40% via reducing the solvent content by ~4%. [ABSTRACT FROM AUTHOR]

A broadband antireflection film was prepared with SiO 2 by glancing angle deposition. The refractive index of the SiO 2 film was tuned from 1.15 to 1.45 by adjusting the deposition angle. A novel broadband antireflection film was designed with the graded index film. The average reflectivity of antireflection film is less than 0.41% between 400 nm and 1800 nm wavelength range at 0° incident angle. • A novel broadband antireflection film design is proposed with the graded index film. • This graded index antireflection film is fabricated by glancing angle deposition technology. • The average reflectivity of antireflection film is less than 0.41% between 400nm and 1800nm wavelength range. [ABSTRACT FROM AUTHOR]

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]