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In this study, four Ta 2 O 5 -based mixture coatings, including Ta 2 O 5 -TiO 2 , Ta 2 O 5 -HfO 2 , Ta 2 O 5 -Al 2 O 3 , and Ta 2 O 5 -SiO 2 , are deposited via plasma-ion-assisted electron-beam co-evaporation and compared with a Ta 2 O 5 monolayer coating. The chemical compositions, microstructures, and optical and femtosecond laser-induced damage threshold (LIDT) properties of the coatings are investigated. For different doping materials, when the refractive indices of the mixture coatings are close, the femtosecond LIDTs exhibit a considerable difference. The experimental results indicate that the Ta 2 O 5 -HfO 2 mixture coating exhibits a larger optical bandgap and higher femtosecond LIDT than other coatings. The 1-on-1 LIDT of the Ta 2 O 5 -HfO 2 mixture coating is approximately 1032.3 mJ/cm2 (170 fs), which is 25% higher than that of the Ta 2 O 5 monolayer coating. We believe the Ta 2 O 5 -HfO 2 mixture will be useful for various multilayer coatings such as chirped mirrors and other mirrors in femtosecond laser applications. • The effect of doping materials on Ta 2 O 5 -X mixtures is systematically studied. • Ta 2 O 5 -X mixtures with similar refractive indices show different optical bandgaps. • The optical bandgap affects the femtosecond laser-induced damage threshold. • The Ta 2 O 5 –HfO 2 mixture coating exhibits excellent performance. [ABSTRACT FROM AUTHOR]

A novel synergistic strategy of N-doping and N-wrapping/bridging to synthesize photosensitive and conductive Graphene-TiO 2 composite nano-capsules for gaseous HCHO degradation was proposed. High HCHO photodegradation activity of the composite was attributed to the enhanced interfacial contact of TiO 2 with conductive melamine-doped graphene (MG) sheets by dopamine (DA) bridging. MG improved the electrical conductivity and photoinduced charges separation/transfer in the MG/TiO 2 composite. Moreover, hydrogen treated DA wrapped/bridged MG/TiO 2 composite (H-TiO 2 @MG-D) forming a 3D nano-capsule structure, which could concomitantly strengthen the interfacial contact between TiO 2 and MG sheets and accelerates electron mobility. Characterization and DFT simulation results revealed that H-TiO 2 @MG-D nano-capsules exhibited the lowest band gap (2.49 eV) and highest charges separation efficiency. Simulation results further indicated that N-doping accelerated the transfer of adsorption sites from acidic Ti 4+ (for HCHO) to basic N sites (for HCOOH and CO 2 ) before and after HCHO degradation reaction. The enhanced interfacial contact of H-TiO 2 @MG-D resulted in its remarkably higher HCHO photocatalytic degradation efficiency ( ŋ  = 92%) and fast degradation rate ( k  = 15.04 × 10 −3  min -1 ) than that of pristine TiO 2 by a factor of 4.1 and 9.2, respectively. Therefore, the present study attributed to ease of synthesis and novel N-doping and N-wrapping strategy for the preparation of highly conductive MG-TiO 2 composite can be deemed as an effective and promising pathway for HCHO photodegradation and other similar photocatalytic applications. [ABSTRACT FROM AUTHOR]

HfO 2 monolayer coatings are grown by plasma-enhanced atomic layer deposition (PEALD), and the effects of the thermal annealing atmosphere and temperature on the surface morphology, crystal structure, chemical composition, optical absorption, and laser-induced damage threshold (LIDT) of the HfO 2 monolayer coatings are investigated. The experimental results show that annealing in an oxygen atmosphere is more beneficial to the decomposition of impurity compounds (carbonates and amines) and the elimination of oxygen deficiency in HfO 2 coating than in a nitrogen atmosphere. Compared to the as-deposited coating, the HfO 2 coating annealed under an oxygen atmosphere and specific temperature has lower C and N impurity contents, a better stoichiometric ratio, and thus lower absorption and higher LIDT. The highest LIDT (at 355 nm) of 6.3 J/cm2 is obtained at an annealing temperature of 700 ℃, which is approximately three times that of the as-deposited coating. We believe that this experimental result can help improve the LIDT of PEALD-grown oxide coatings or other oxide coatings containing similar impurities. • The effect of annealing on the properties of PEALD HfO 2 coatings is investigated. • The carbonates and amines in the HfO 2 coating decompose during annealing. • The oxygen-annealed HfO 2 coating has lower absorption and higher LIDT. • The oxygen-annealed HfO 2 coating shows different damage morphology. [ABSTRACT FROM AUTHOR]

N-doped hydrophobic microporous carbons (N-PCs) derived from dopamine were synthesized by using different methods. The effects of their graphitic C/N, basic N groups as well as oxygen content on the competitive and selective adsorption towards p-xylene were systematically studied in this work. The synthesized N-PCs possessed higher amount of sp 2 C/N than some known activated carbons, enhancing their adsorption interaction towards weakly-polar p-xylene. Meanwhile, the pyrrolic/graphitic N groups and oxygen deficiency could also improve the water resistance of the N-PCs. Temperature programmed desorption (TPD) and inverse gas chromatography (IGC) results showed that the hydrogen-treated HN-PC surface had much higher special interaction towards weakly polar VOCs but lower interaction with H 2 O than other selected carbon materials with lower sp 2 C, free-N and richer O content. Breakthrough experiment of p-xylene/water mixture depicted that the HN-PC samples maintained a very high working capacity of p-xylene (>5.1 mmol/g) at 80% relative humidity. This value was approximately 1–3 times greater than that of some activated carbon and MOF materials. Besides, its diffusion rate constant ( k b ) of p-xylene was also undisturbed by water molecules. Thus, it can be seen the novel porous N-PCs with high water-resistance can become a good candidate for VOCs pollution control under humid air. [ABSTRACT FROM AUTHOR]

A novel enhanced hydrophobic MIL(Cr) metal-organic framework was obtained by using naphthalene dicarboxylic acid as ligand and its adsorption equilibrium, diffusion kinetics and competitive adsorption for benzene and water were investigated systematically. Results show that: (1) the MIL(Cr)-Z1 possessed similar crystal structure and morphology to the MIL(Cr)-101. It had high surface area of 3008 m 2 /g with smaller window apertures (6.9 Å) and pore cages (23.3 Å) than MIL(Cr)-101; (2) it had high benzene uptake of ∼7.0 mmol/g with the isosteric heat of ∼51 kJ/mol and high benzene diffusivity (30–40 times quicker than water molecules); (3) it showed an improved hydrophobic property with very low adsorbed amount for water vapor, only about 9.84 mmol/g and 13% of that on MIL(Cr)-101 at 80 RH% and 298 K; (4) breakthrough curves show that MIL(Cr)-Z1 had high working capacity for benzene, which was 58% higher than that of MIL(Cr)-101 at 60 RH%. Thus, high adsorption capacity and selectivity for benzene VOCs make enhanced hydrophobic MIL(Cr)-Z1 a promising candidate for benzene VOCs capture under high-moisture environments. [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]

Plate laser beam splitter (PLBS) coatings for intensity-splitting in high-power laser applications face increasing requirements, where the challenge is to simultaneously satisfy a given transmittance (T)/reflectivity (R) intensity-splitting ratio with a certain bandwidth, and a high laser damage threshold (LIDT). Traditionally, a given T/R ratio is achieved by using a non-quarter-wave design. We propose a quarter-wave design strategy for arbitrary T/R ratios by using mixture layers with tunable refractive index (n) and optical bandgap as high- n layers. Two quarter-wave PLBS coatings based on HfO 2 –Al 2 O 3 mixture with a designed T/R ratio of 50:50 are experimentally demonstrated and compared with the traditional PLBS coating. The mixture-based PLBS coating shows good spectral performance, low surface roughness, and high LIDT. For an s -polarized 8 ns pulse laser at a wavelength of 1064 nm, a mixture-based PLBS coating design can improve LIDT by a factor of ∼ 2 with a slightly wider bandwidth. This tunable mixture-based PLBS coating design strategy provides support for the increasingly high output power of high-power laser systems. [ABSTRACT FROM AUTHOR]

We describe the design, fabrication and performance of an optimized one-dimensional subwavelength grating for use in 1064 nm wavelength laser systems. The laser-induced damage threshold (LIDT) under the irradiation of 12 ns 1064 nm pulses on the grating was performed, and a higher LIDT was obtained compared with LIDT of traditional antireflective coatings. Laser irradiation produces some morphological modifications on grating. Light interferometric surface profiler, scanning electron microscope and atomic force microscope were used to study these modifications, and these studies indicate the significant ablation and resolidification have occurred. To understand possible damage mechanisms, the role of electric field distribution inside the grating during the laser radiation process was investigated by a three-dimensional finite difference time-domain method, and the simulation result indicates the temperature distribution resulting from the internal electric field may be the main factor behind the damage. [ABSTRACT FROM AUTHOR]

[Display omitted] • First studied on the properties of mixture coating for picosecond laser applications. • Systematically studied the influence of Al 2 O 3 doping and annealing on the properties of HfO 2 -Al 2 O 3 mixture coating. • The properties of the mixture coatings may be improved by increasing the doped Al 2 O 3 content and annealing treatment. • Provide significantly support for the preparation of reflective coatings with a higher picosecond damage threshold. HfO 2 -Al 2 O 3 mixture coatings with different Al 2 O 3 doping contents are deposited on fused silica substrate using an electron-beam co-evaporation process. The effects of the material composition and thermal annealing temperature on the chemical states, crystal structure, transmittance spectra, refractive index, optical band gap, and picosecond laser-induced damage threshold (LIDT) properties of these HfO 2 -Al 2 O 3 mixture coatings are investigated. Characterization measurements confirmed that the properties of the mixture coatings may be improved by increasing the doped Al 2 O 3 content and thermal annealing. The experimental results show that, firstly, with the increase of the doped Al 2 O 3 content, the optical band gap and the LIDTs of the HfO 2 -Al 2 O 3 mixture coating increase monotonically. Secondly, the highest LIDT of 7.1 J/cm2 is obtained at an annealing temperature of 500 °C, which is ∼ 20 % higher than that of the as-deposited coating. The S-M 2 coating annealed at 500 ℃ shows a similar LIDT and a higher refractive index as compared to the pure Al 2 O 3 , which provides significantly support for the preparation of reflective coatings with a higher picosecond damage threshold. [ABSTRACT FROM AUTHOR]

Abstract: Four mirror coatings were designed for transporting 1064nm light, and prepared under the same process parameters. The laser induced damage threshold (LIDT), electric field distribution, as well as the damage morphology of the prepared transport mirror coating was investigated. The results indicate that the SiO2 overcoat layer and electric field distribution have a great impact on the LIDT and damage morphology of the transport mirror coating. A thicker SiO2 overcoat layer can suppress the delamination damage morphology, and significantly increase the LIDT. For the designs with similar SiO2 overcoat layer thickness, the nano-absorbing defects can survive at higher laser fluence in the design with lower electric field intensity. In addition, the HfO2 over SiO2 interface has a better interfacial strength and less “invisible” nano-absorbing defects than the SiO2 over HfO2 interface, suggesting that improving the SiO2 over HfO2 interfacial quality will be an effective way to enhance the laser damage performance of the transport mirror coating. [Copyright &y& Elsevier]

Abstract: Antireflective sub-wavelength structures with high laser-induced damage threshold on fused silica are fabricated using a self-assembly technique, in which a porous yttrium oxide film is deposited as a mask followed by alkaline etching. By controlling the etching time, several sub-wavelength structures with different height, density and diameter have been made. The best reflectance is less than 2.87% for wavelengths from 300 to 1000nm after 1.5h etching. The laser-induced damage threshold of the etched glass measured by a 10ns Nd:YAG laser at a wavelength of 532nm was as high as 30J/cm2 compared to 16J/cm2 of blank glass. The specular reflectance of structures matches the theoretical simulation using a thin-film multilayer model, and the results reveal that the shape of the structures is similar to the calculated parabolic shape. Achieving antireflective sub-wavelength structures on fused silica paves the way for applications in laser systems. [Copyright &y& Elsevier]

Abstract: We present a monitoring strategy based on using two pieces of witness glass, which are brought to the measuring position in a specially chosen sequence, each witness glass is monitored by one single wavelength. To reduce the thickness error, some thick layers are divided into two layers and monitored by different witness glasses. Theoretical analysis and experimental results have demonstrated that the proposed monitoring strategy can achieve spectral performance close to the theoretical design. [Copyright &y& Elsevier]

Optimal sub-wavelength structures (SWS) with parabolic hole on glass substrate are designed using effective medium theory (EMT), which will reduce the reflectance over wavelength range from 300 to 1200nm and 0° to 80° angle of incidence. The performance of SWS integrated glass is verified by genetic algorithm. The optimized SWS with the cross-sectional profile of parabolic hole have parameters with ∼120nm diameter and 300nm height. The average reflectance over wavelength range from 300 to 1200nm and 0° to 80° angle of incidence could be reduced to only 0.5% by applying the optimized SWS onto glass. [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]

Abstract: Porous antireflective (AR) coatings were prepared by the neutral solution leaching of borosilicate glass. The textured surfaces typically exhibit broadband and wide-angle AR behavior with an extremely low scattering over 300–1400nm spectral range. The coating thickness increases with increase in the solution concentration, temperature and etching time, leading to the tunable transmittance spectra in the entire wavelength range. And the thickness and corresponding refractive index of AR coatings can be calculated using transmittance simulation. The relationship of experimental variations, coating thickness and etching rate was obtained and discussed. These porous AR coatings with controlled thickness and refractive index would have broad potential applications. [Copyright &y& Elsevier]

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]

The laser-induced damage threshold (LIDT) of HfO 2 /SiO 2 anti-reflection (AR) films for ultraviolet (UV) lasers was improved via low-temperature plasma-enhanced atomic layer deposition (PEALD). Focused on the chemical composition, optical absorption, surface scattering, and laser-resistance, the impact of precursor exposure time on PEALD SiO 2 film properties and growth temperature on PEALD SiO 2 and HfO 2 film properties were investigated respectively. When irradiated by UV laser, PEALD SiO 2 film exhibits a higher LIDT than the PEALD HfO 2 film, which is consistent with their less impurity content and lower absorption. A bilayer structure HfO 2 /SiO 2 AR film for 355 nm laser was designed and experimentally demonstrated via PEALD growth at a temperature of 150 °C. The prepared PEALD AR film shows a reflectance <0.2% at 355 nm as designed and better laser-damage resistance with a LIDT of 24.4 J/cm2 (355 nm, 7.8 ns) than the conventional e-beam deposition method. Image 1 • The HfO 2 /SiO 2 anti-reflection film for UV laser was presented via low-temperature PEALD. • The presented PEALD AR film shows better laser-damage resistance than conventional e-beam deposition method. • The impact of precursor exposure time on PEALD film properties were investigated. • The XPS measurement shows the impurity content of PEALD HfO 2 film is high, leading to a large absorption and low LIDT. [ABSTRACT FROM AUTHOR]

• Deeper understanding of moisture-induced instability of electron-beam coatings was achieved by prolonging the originally rapid water adsorption process with a dense capping layer. • Water transport in electron-beam coatings included four steps: filling, stabilization, swelling and refilling. • Water molecule content and structure evolution led to the increasing compressive stress evolution at the first stage and subsequent transition from compressive to tensile stress evolution. • A model based on the finite element method was proposed to calculate the water vapor transmission rate of electron-beam coatings. The moisture-induced instability of electron-beam (e-beam) coating can even result in the performance instability of a large laser system. A dense plasma-ion-assisted-deposition SiO 2 capping layer was employed to isolate the top surface of the coating from ambient humidity and extend the originally rapid water adsorption process, allowing a deeper understanding of the instability of e-beam coatings caused by moisture. Spectral measurements suggested that four water adsorption steps, including filling, stabilization, swelling and refilling, led to the overall redshift and short-term fluctuations in spectra. The stress and Fourier transform infrared analysis revealed that water adsorption and ice-like/ice structure water was responsible for the increasing compressive stress evolution at the first stage and subsequent transition from compressive to tensile stress evolution, respectively. A model based on the finite element method was proposed to calculate the water vapor transmission rate of e-beam coatings. Our study on the underlying mechanism of moisture-induced instability of e-beam coating is helpful to ensure the reliability and stability of large laser systems. [ABSTRACT FROM AUTHOR]

• HfO 2 –SiO 2 mixture coatings with different proportions were investigated. • Admixing 10% or higher SiO 2 in the mixture coatings suppresses inhomogeneity of HfO 2. • Short-wave pass dichroic laser mirror coatings were prepared using mixture layers. • Using HfO 2 –SiO 2 mixture layers fundamentally solves the half-wave hole effect. • Using different mixture layers gets further optical improvement in the pass band. Hafnia/silica (HfO 2 /SiO 2) short-wavelength pass dichroic laser mirror (DLM) coatings are widely utilized in high-power laser systems. However, the half-wave hole effect resulting from the refractive index inhomogeneity of HfO 2 severely restricts the spectra and potential applications of these coatings. To address this issue, an investigation was conducted on HfO 2 –SiO 2 mixture coatings with different proportions, which were produced by electron beam co-evaporation. Compared to the inhomogeneous growth characteristics observed in pure HfO 2 coatings, the introduction of 10 % or higher SiO 2 admixing in HfO 2 –SiO 2 mixture coatings results in an amorphous structure characterized by excellent refractive index homogeneity and improved surface smoothness. Leveraging this, different DLM coatings with the objective of achieving high transmittance across the 400 to 900 nm range were designed and prepared, while ensuring high reflectance at 1064 nm. The incorporation of HfO 2 –SiO 2 mixture layers instead of pure HfO 2 layers in the mirror coatings led to a fundamental inhibition of the half-wave hole effect throughout the entire broad transmission band, resulting in a substantial improvement in the optical performance of the coatings. Moreover, by incorporating several types of HfO 2 –SiO 2 mixture layers with different proportions in the coating stacks, the transmittance of DLM coatings in the pass band can be further increased, and the transmission fluctuations at different wavelengths can be further compressed. Additionally, compared to traditional DLM coatings with HfO 2 layers, DLM coatings incorporating HfO 2 –SiO 2 mixture layers exhibit lower roughness, higher laser-induced damage threshold (LIDT) at 532 nm, and similar LIDT at 1064 nm. These results indicate a promising strategy for fabricating DLM coatings tailored for high-power laser systems. [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]

High N-doped porous graphitic carbons (S-NPGCs) with multi-flaky shell hollow structure were prepared by using CaCO3 as a green/useful template. S-NPGCs exhibit very fast adsorption for toluene (31 times that of HKUST-1) and effectively selective enrichment of small peptides with high inhibitory activity of angiotensin converting enzymes. [ABSTRACT FROM AUTHOR]

A broadband metamaterial absorber (MA) based on the titanium nitride (TiN) nano-disk array is studied using finite difference time domain simulations. The semiconducting indium tin oxide (ITO) thin film is introduced as the space layer in this sandwiched structure. Utilizing the symmetrical geometry of the MA structure, polarization insensitivity of the broadband absorption was gained. The absorber with TiN nano-disk array shows a peak absorbance of 99 % and larger than 98 % from 560 to 675 nm by numerical simulation. This compact design may have potential applications in the plasmonic sensing and photovoltaic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Light-induced phase transition to spinel oxide via light-irradiated LDH. • Phase transition mechanism is proposed as "Metallic bond breakage-Co oxidation". • Light absorption, charge separation and toluene adsorption are optimized. • Superior flowing toluene catalytic activity and stability to reported catalysts. • In-situ DRIFT reveals "tandem photothermal catalysis" mechanism. Low temperature fabrication of spinel oxides and development of efficient and durable toluene photothermal catalysts remain challenging. Herein, two-dimensional amorphous spinel CoAlO x nanosheets (CoAl-LDH-L2) have been fabricated via a light-induced phase transformation strategy using intense photooxidation. Light-induced decomposition and phase transformation process have been used to elucidate the growth mechanism. The CoAl-LDH-L2 exhibits improved toluene adsorption and photothermal conversion, with the highest photothermal catalytic toluene conversion (∼100 % at 500 ppm) at 90 °C, outperforming most previously reported catalysts. Irradiation with mild external heating significantly increases the mineralization rate (∼90 %) and improves the long-term and cycling stability (∼5% losses within 39 h) relative to that under single-light-driven conditions. In-situ DRIFT spectroscopy was also performed for revealing the "tandem photothermal catalysis" mechanism for toluene conversion. This work offers a novel strategy for developing spinel oxides as low-temperature photothermal catalyst in a green and sustainable way. [ABSTRACT FROM AUTHOR]

• Four hybrid materials (HfO 2 /Al 2 O 3 nanolaminate, HfO 2 /SiO 2 nanolaminate, HfO 2 -Al 2 O 3 mixture, and HfO 2 -SiO 2 mixture coatings) are investigated. • Hybrid materials show suppressed crystallization and reduced surface roughness, enabling tunable bandgaps and optical constants. • Hybrid-material-based mirror coatings are investigated and mixture-based mirror coatings have the highest LIDT. • The damage initiation mechanism of the mirror coating varies around 3 ps for laser pulses ranging from 0.5 to 8 ps.. Four hybrid materials (HfO 2 /Al 2 O 3 nanolaminate, HfO 2 /SiO 2 nanolaminate, HfO 2 –Al 2 O 3 mixture, and HfO 2 –SiO 2 mixture) and four hybrid-material-based mirror coatings are prepared via electron-beam evaporation. The refractive index (n), optical bandgaps, and microstructural properties of the hybrid materials are investigated and compared with those of pure materials. Experimental results show that the hybrid materials suppress crystallization, reduce surface roughness, and provide tunable bandgaps and optical constants. Among the four hybrid materials with similar n values, the HfO 2 –Al 2 O 3 mixture shows the largest bandgap. All the hybrid-material-based mirror coatings exhibit a higher laser-induced damage threshold (LIDT) at 8 picosecond (ps) than the conventional pure-material-based mirror coating. The HfO 2 –Al 2 O 3 mixture-based mirror coating with a relative high LIDT is used for further study of the pulse width dependence of the LIDT, and shows superior LIDT over the conventional mirror coating at 0.5 ps, 1 ps and 3 ps. Typical damage morphological features induced at different pulse widths show that the damage-initiation mechanism of the mirror coating changes around 3 ps. [ABSTRACT FROM AUTHOR]

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]

Background: Weifuchun (WFC), a Chinese herbal prescription consisting of Red Ginseng, Isodon amethystoides and Fructus Aurantii, is commonly used in China to treat a variety of chronic stomach disorders. The aim of the paper was to determine the effect of WFC on intestinal microbiota changes in precancerous lesions of gastric cancer (PLGC) patients. Methods: PLGC patients of H. pylori negative were randomly divided into two groups and received either WFC tablets for a dose of 1.44 g three times a day or vitacoenzyme (Vit) tablets for a dose of 0.8 g three times a day. All patients were treated for 6 months consecutively. Gastroscopy and histopathology were used to assess the histopathological changes in gastric tissues before and after treatment. 16S rRNA gene sequencing was carried out to assess the effects WFC on intestinal microbiota changes in PLGC patients. Receiver Operating Characteristics (ROC) analysis was used to assess the sensitivity and specificity of different intestinal microbiota in distinguishing between PLGC patients and healthy control group. Results: Gastroscopy and histopathological results indicated that WFC could improve the pathological condition of PLGC patients, especially in the case of atrophy or intestinal metaplasia. The results of 16S rRNA gene sequencing indicated that WFC could regulate microbial diversity, microbial composition, and abundance of the intestinal microbiota of PLGC patients. Following WFC treatment, the relative abundance of Parabacteroides decreased in WFC group when compared with the Vit group. ROC analysis found that the Parabacteroides could effectively distinguish PLGC patients from healthy individuals with sensitivity of 0.79 and specificity of 0.8. Conclusions: WFC could slow down the progression of PLGC by regulating intestinal microbiota abundance. Trial registration NCT03814629. Name of registry: Randomized Clinical Trial: Weifuchun Treatment on Precancerous Lesions of Gastric Cancer. Registered 3 August 2018-Retrospectively registered, https://register.clinicaltrials.gov/ NCT03814629. [ABSTRACT FROM AUTHOR]

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]

In this paper, we present a glass-based double-side cascade film stack structure for visible-infrared ultrabroadband absorption. The proposed structure demonstrates an average absorption as high as ∼95% over an ultrawide range of wavelengths from 0.4 μm to 20 μm. The high absorption feature of the different bandgap materials is applied in this absorption device to realize the ultrabroadband absorption, combining with the metal-dielectric-like configuration for those unmatched-admittance wavelengths and the graded index profile arrangement for the 0.4–2.5 μm band. The proposed ultrabroadband absorber shows a great angular tolerance up to 60° with the average absorption of 90% remaining. The proposed approach can have tremendous potential in fields of optical sensing, camouflage, optical imaging, passive cooling, and sustainable power generation, profiting from the good mechanical characteristics of this compact multilayer film structure and the low manufacture costs with the simple physical vapor deposition. [ABSTRACT FROM AUTHOR]

Large-scale layers peeling after the laser irradiation of dual ion beam sputtering coatings is discovered and a model is established to explain it. The laser damage morphologies relate to the laser fluence, showing thermomechanical coupling failure at low energy and coating layers separation at high energy. High-pressure gradients appear in the interaction between laser and coatings, resulting in large-scale layer separation. A two-step laser damage model including defect-induced damage process and ionized air wave damage process is proposed to explain the two phenomena at different energy. At relatively high energies (higher than 20 J/cm2), ionization of the air can be initiated, leading to a peeling off effect. The peeling effect is related to the thermomechanical properties of the coating materials. [ABSTRACT FROM AUTHOR]

• The PI alignment layer is pinned on the ITO film to imitate the structure of an LCD. • The damage of the samples are attributed to the high absorption of the ITO film. • The mechanical properties of the PI are primarily responsible for the LIDT result. This report focuses on the damage characteristics of the indium-tin-oxide (ITO) layer and the polyimide (PI) layer, which are two constituent components of a LCD. This investigation is different from the previous study, in which the alignment layer was deposited directly on a glass substrate. The PI alignment layer is pinned on the ITO film to imitate the structure of the LCD as much as possible in our current study. The damage process of the ITO/Glass sample involves melting, vaporization near the laser-induced damage threshold (LIDT), and removal at a higher fluence. However, the damage process of the PI/ITO/Glass sample involves thermally induced plastic deformation, followed by cooling when the irradiation fluence is near the LIDT, and rupture when the irradiation fluence is higher. The LIDTs of the PI/ITO/Glass samples, as determined by the on-line CCD detection technique, are higher than those of the ITO/Glass samples. The favorable mechanical properties of the PI are primarily responsible for this result. [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]

We investigate the influence of a protective layer on the picosecond laser-induced damage in HfO 2 /SiO 2 high-reflective (HR) coatings. Two types of 1064-nm HR coatings, with and without a SiO 2 protective layer, are deposited using electron beam evaporation. Laser-induced damage tests are operated with 1064-nm, 30-ps laser pulses in one-on-one mode. Five different angles of incidence (AOIs) are considered in the tests for both coatings, in order to modulate the electric field ( E -field) intensity in the HR coatings. The damage morphologies and cross-sections of the damage sites are characterized using scanning electron microscope (SEM) and focused ion beam (FIB), respectively. Experimental results show that the SiO 2 protective layer slightly improves the laser-induced damage threshold (LIDT) of the HR coatings for all AOI values. The damage morphology contains high-density micrometer-scale pits and layer delaminations, at low and high fluences, respectively. The cross-sections of the damage sites and LIDTs for different AOIs are compared with corresponding E -field distributions. For both coatings, the damage is initiated near the peak of the E -field. A negative linear relationship is observed between the LIDT and corresponding maximum E -field intensity for both 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]

A facile L-cysteine-assisted route for the preparation of capsule-like Cu2SnS3 crystals with high uniformity and yield was reported. The as-synthesised samples were characterised by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS), transmission electron microscopy (TEM), Raman spectrum and UV–Vis spectroscopy. The Cu2SnS3 nanocapsules were 200–500 nm in width and up to 2 μm in length. Results showed that the structure of the nanocapsules was cubic phase which had stoichiometric composition, good crystallinity and capsule-like morphology. Importantly, the effects of solvents on the structure and morphology of the product were investigated. A possible mechanism for the growth of capsule-like Cu2SnS3 nanostructures was also proposed. [ABSTRACT FROM AUTHOR]

The plasma scald damage is the most typical laser damage morphology presented on the laser conditioned HfO 2 /SiO 2 mirrors. In order to provide guidance for defining the acceptance quantitative specification for the plasma scald on these laser conditioned mirrors, the simulations about the downstream beam modulations of the plasma scald are investigated based on its damage characteristics and the diffraction theory. The single plasma scald with the typical size, induced by the laser conditioning, can hardly cause damage to the downstream optics and its influence on the beam contrast can be reduced easily with the increment of the propagation distance. Those with small size and large depth, or those with big size and shallow depth can also hardly induce downstream damage, but the beam contrasts become worse with the increment of the size of the concave part as well as its depth. For a maximum plasma scald observed on the laser conditioned mirror, the intensity modulation peak is close to 1.3 and the beam contrast reaches to 25% even at 2 m downstream from the mirror. For multi plasma scalds, more diffraction rings show up in the downstream beam and further decrease the overall uniformity of the beam. The uniformity of the beam gets worse as the number of the plasma scald is increased. When the density of the plasma scald with the typical size in these 1ωHfO 2 /SiO 2 mirrors reaches 20 per 1 cm 2 , the beam contrast is less than 6%. [ABSTRACT FROM AUTHOR]

• By adding a large-angle long-wave pass filter, a spectrum analyzer was developed. • The Raman spectra excited by a high-power laser and low-power laser were compared. • Significant differences related to the molecular vibration were detected. • The emission spectra in the damaged and undamaged sites were compared. High-power laser-induced spectrum analyzer was applied to reveal transient material variations in KDP/DKDP crystals. A long-wave pass large-angle filter structure was used to efficiently filter the high-power laser-induced Rayleigh scattering. The Raman spectra excited by a high-power nanosecond laser were compared with that by a low-power continuous-wave (CW) laser. Significant increase of Raman spectra related to the molecular vibration of hydroxyl and hydrogen bonds (1000–3000 cm−1) under high-power laser were obviously detected. The emission spectra in the damaged and undamaged sites were compared. It was found that the intensity of the Raman scattering decreased, and an emission peak at 467 nm was detected after the damage. Moreover, stronger intensity of the stimulated Raman scattering corresponds to higher laser damage threshold. Based on these results, the generation of transient defects was discussed. The irradiation of the high-power laser provided sufficient energy for the intense vibration of hydroxyl and hydrogen bonds, thus breaking bonds and generating transient defects. Furthermore, the energy level of the defects corresponded to the emission peak centered at 467 nm, thereby becoming the precursor of laser damage. [ABSTRACT FROM AUTHOR]

• Accurate ε , σ , α of thickness controlled MoS 2 films are obtained experimentally. • The evolution of critical points with film thickness has been revealed. • The transitions of critical points were assigned into electronic band structure. • Excitonic binding energies were traced as a function of the number of layers. • The quantum confinement effect was largely weakened more than four layers. We systemically investigate the effects of quantum confinement on the excitonic property and electronic band structures of centimeter-scale MoS 2 films (number of layers: N = 1, 2, 4, and 18) through spectroscopic ellipsometry. The optical properties including optical conductivity, exciton binding energy and critical points (CPs) are traced as a function of layer number. We find that A and B excitons have the largest binding energies in monolayer MoS 2 compared with the values in multilayer MoS 2 because of the absence of interlayer coupling in former. Nevertheless, the peak positions of A and B excitons are almost the same, even when the layer number changes. This is because of the canceling out of differences between quasi-particle band gap and excitonic binding energy. Furthermore, the threshold energies of the eight CPs are calculated; using these values, the valence and conduction band alignments of the CPs are determined. It is noteworthy that the electronic band structures of MoS 2 become stable when the layer number is more than four, which can be attributed to the largely weakened quantum confinement effect in these cases. The results of our study help us better understand the effect of quantum confinement on photoelectronic and photovoltaic applications using MoS 2 films. [ABSTRACT FROM AUTHOR]