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Abstract: Broadband antireflection (AR) nanostructure arrays patterned directly into a bulk substrate, behaving as the expected performance of high laser induced damage threshold (LIDT), is proposed for the application of laser-transmitting optical elements. These regular periodic arrays known as “moth-eye” structure exhibit particularly noteworthy AR property over a wide spectrum and over a large field of view in addition to overcome efficiently the disadvantages of multilayer AR thin-film. Furthermore, the near-field distribution in nanostructure arrays with respect to the period, the groove depth and incident angle, respectively, was numerically simulated using a rigorous Fourier modal method (FMM). It is interesting that the maximum value of the normalized electric field intensity is obviously distributed inside the air layer upon the nanostructure for the periodicity of 100nm, which has significant potential to reach to ultra high LIDT for the application of short-pulse high-power laser system. Besides, the variation of the near-field distribution inside the nanostructure arrays exhibits critically dependent on the period of surface structure, but the effect caused by the discrepancy in groove depth and incident angle is unimportant. [Copyright &y& Elsevier]

Abstract: The damage probability and damage morphology of the multilayer dielectric films under two wavelengths simultaneous irradiation are investigated. The damage morphology result shows that both pit number and depth caused by simultaneous 1ω and 3ω irradiation increase sharply compared with 3ω irradiation alone. The damage probability results demonstrate that the damage probability magnification ratio of the coupled wavelengths is bigger than 1, especially when 1ω and 3ω all held at near LIDT, the magnification ratio of the damage probability is 7–8, and these results are similar to a recent muti-wavelength damage study about KDP crystal. [Copyright &y& Elsevier]

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

Abstract: The 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: Optical filters composed of Ag, , and ZnSe films were prepared on BK7 substrates by evaporation. By employing spectrophotometer, microscope, scanning electron microscope (SEM), and energy dispersive spectrum (EDS) analysis, the moisture-dependent stability of the samples was tested. The experimental results revealed that filter failure often occurs initially at defect sites. Small sputtering particles and pinhole are found to be two types of defects that induced the optical coating filter failure. The mechanisms of the defect-induced failure of the filters also are discussed in the article. [Copyright &y& Elsevier]

Abstract: ZnO/MgF2/ZnO sandwich structure films were fabricated. The effects of a buffer layer on structure and optical properties of ZnO films were investigated by X-ray diffraction, photoluminescence, optical transmittance and absorption measurements. Measurement results showed that the buffer layer had the effects of improving the quality of ZnO films and releasing the residual stresses in the films. The near-band edge emissions of ZnO films deposited on the MgF2 buffer layer were significantly enhanced compared with those deposited on bare substrate due to the smaller lattice mismatch between MgF2 and ZnO than that between fused silica and ZnO. [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: Some results of an investigation on the layer thickness uniformity of glancing angle deposition are presented. A zirconia monolayer has been deposited by glancing angle deposition to analyze the layer thickness uniformity. The experimental results indicate that the thickness variation over the substrate is less than 0.1%, which is considered as good uniformity. It is found that the non-uniformity of experimental results is larger than that of the theoretical results. [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]

• 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]

To analyze the mechanism of damage threshold enhancement after laser conditioning, the fluorescent and stimulated Raman scattering properties of unconditioned and laser-conditioned KD2PO4 crystals are compared in detail. It is revealed that the intensity of fluorescence decreases significantly, especially fluorescence <400 nm, after nanosecond laser conditioning, and the change of the stimulated Raman scattering peak at 921 cm − 1 is very weak. Moreover, the intensity of fluorescence further decreases after subnanosecond laser conditioning. A sharp decrease in the fluorescence intensity <400 nm reflects a change in energy levels of the electron defects in a crystal. The Raman scattering proves very weak change of the PO4 vibrational modes. Furthermore, a laser-conditioning mechanism is discussed in combination with electronic transition and thermal processes. [ABSTRACT FROM AUTHOR]

In the current solution for multiwavelength achromatic flat lenses, a one-to-one correspondence exists between the number of writing phase distributions and the number of achromatic wavelengths. Breaking this correspondence requires a complex phase design and parameter optimization. Here, we show that a dual-layer cascade liquid crystal Pancharatnam-Berry lens (CLCPBL) with two writing phase distributions and a specific coupled phase distribution between the layers can achieve three wavelength achromaticity without any parameter optimization process. Similarly, in a three-layer cascade, the number of achromatic wavelengths increases to seven through the permutations of the layers, with adjustable amplitude factors. We fabricate a three-layer CLCPBL with the design wavelengths of 396.8 nm, 1064 nm, and 1550 nm, which theoretically allows the light at 632.8, 532.8, 3383 and 450 nm to form a common focus, and test such structure. Our CLCPBL enables a wider range of applications than conventional achromatic flat lenses. Metalenses are lightweight and compact alternative to achromatic lens assemblies, but they usually fulfill the focusing requirements for a single wavelength. The authors design and fabricate a cascade liquid crystal Pancharatnam-Berry lens that enables a seven-wavelength achromatic focusing in a broad range of frequencies. [ABSTRACT FROM AUTHOR]

Mid‐infrared (MIR) pulsed lasers operating at 2–5 µm have important applications in communication, sensing, and medicine. However, the lack of robust MIR saturable absorbers (SAs) remains a major obstacle. Here, a semiconductor material cadmium oxide (CdO) film with high laser‐induced damage threshold (800 nm, 134 mJ cm−2) and broadband saturable absorption (2.0–3.9 µm) is investigated. The effective tuning of the nonlinear optical response of CdO is demonstrated by adjusting the carrier concentration via a tungsten (W)‐doping scheme. The saturable absorption is improved and carrier relaxation process is accelerated after increasing the W‐dopant level. Based on these findings, the robust CdO‐SAs with customizable parameters are realized and Q‐switched lasers with decreasing pulse width from 372 to 254.3 ns are obtained at 2 µm. The design flexibility provided by CdO opens up a large parameter space that enables the continuous improvement of compact and high‐performance MIR ultrafast lasers. [ABSTRACT FROM AUTHOR]

This paper presents a simple system capable of detecting wavefront information in the wavelength range of 488–1064 nm based on an interferometric system consisting of a ball lens and an aspheric collimator. The design is conducive to short-distance Gaussian beam expansion and collimation at multiple wavelengths. The design principles and performance of the system are described in detail; the measurement precision of the system is verified experimentally by measuring the surface profile of a piece of uncoated N-BK7 glass at various test wavelengths with the proposed setup and with a digital 4D FizCam 2000 interferometer. The highly consistent measurement results of the two methods reveal that the proposed system operates precisely and effectively at various wavelengths. Subsequently, the system is applied to measure the transmitted-wavefront error of a solar filter at a wavelength of 808.0 nm; the measurement results show superb repeatability. The proposed technique avoids the shortcomings of conventional single-working-wavelength interferometric systems, which can neither work in a wide spectrum with high precision nor measure the wavefront properties of many optical bandpass elements in one device; this technique also provides technical support for future applications of high-precision and low-cost wavelength-switchable laser interferometers. [ABSTRACT FROM AUTHOR]

The measurement of the spectral diffraction efficiencies of a diffraction grating is essential for improving the manufacturing technique and for assessing the grating’s function in practical applications. The drawback of the currently popular measurement technique is its slow speed due to the hundreds of repetitions of two kinds of time-consuming mechanical movements during the measuring process (i.e., the rotation of the mechanical arm to capture the light beam and the mechanical variation of the output wavelength of the grating monochromator). This limitation greatly restricts the usage of this technique in dynamic measurement. In this manuscript, we present a motionless and fast measurement technique for obtaining the spectral diffraction efficiencies of a plane grating, effectively eliminating the aforementioned two kinds of mechanical movements. Herein, the proposed solution for removing the first kind of mechanical movement is tested, and the experimental result shows that the proposed method can be successfully used to measure the plane transmission grating’s spectral diffraction efficiencies in the wavelength range of 550-750 nm. The method for eliminating the second kind of mechanical movement is not verified in this manuscript; however, we think that it is very straightforward and commercially available. We estimate that the spectral measurement can be achieved on a millisecond time scale by combining the two solutions. Our motionless and fast measuring technique will find broad applications in dynamic measurement environments and mass industrial testing. [ABSTRACT FROM AUTHOR]

We present a concept of surface decomposition extended from double Fourier series to nonnegative sinusoidal wave surfaces, on the basis of which linear ion sources apply to the ultra-precision fabrication of complex surfaces and diffractive optics. The modified Fourier series, or sinusoidal wave surfaces, build a relationship between the fabrication process of optical surfaces and the surface characterization based on power spectral density (PSD) analysis. Also, we demonstrate that the one-dimensional scanning of linear ion source is applicable to the removal of mid-spatial frequency (MSF) errors caused by small-tool polishing in raster scan mode as well as the fabrication of beam sampling grating of high diffractive uniformity without a post-processing procedure. The simulation results show that optical fabrication with linear ion source is feasible and even of higher output efficiency compared with the conventional approach. [ABSTRACT FROM AUTHOR]

The knowledge of the optical properties of coating materials at high temperatures is important for understanding the dynamic process of high-power laser-material interactions. In this paper, the variations of refractive index and physical thickness of single layer coatings were studied by ellipsometric spectroscopy at different temperatures. From 23 °C to 320 °C, a decrease and then an increase of the refractive index of SiO 2 , and HfO 2 single layer was observed, while the thickness of these layers increased first and then decreased. The inflection points of different coating materials occurred at different temperatures. Water evaporation processes, densification and hydrophilicity of films were used to explain the temperature dependent properties of the dielectric coatings. Results of the variation of refractive index and thickness of single layer coatings at different temperatures in the vacuum proved the mentioned theory. Moreover, HfO 2 single layer shows better resistance to both temperature change and vacuum change, indicating that it is promising for high-reflective coatings in photoelectric devices. Besides, the formation of transient defects during high power laser irradiation was interpreted considering the optical properties variation with temperature. Three confusing and debated issues concerning laser-coating interaction are interpreted and explained. • Change of coatings' optical constants with temperature were studied. • Mechanism relies on water evaporation, film densification and hydrophilicity. • Three confusing issues concerning laser-coating interaction are interpreted. [ABSTRACT FROM AUTHOR]

Single and 10-pulse laser-induced surface damage behaviors of fused silica were investigated using a linearly polarized 40-fs Ti: sapphire laser system operating at a central wavelength of 800 nm. After the sample was subjected to single-shot laser irradiation, it displayed a typically damaged crater, and two types of laser-induced periodic surface structures (LIPSS) on the surface of the damage crater were found under 10-pulse laser irradiation. By increasing the laser fluence, the LIPSS orientation rotated by 90°, and the period changed from 300 nm to 700 nm. Under near-threshold laser irradiation, an intermittent LIPSS, whose orientation was perpendicular to the laser beam polarization direction and average spatial period was around 300 nm, was found on the damaged area. Another type of LIPSS, which was parallel to the laser beam polarization and had a period of approximately 700 nm, was continuously formed at the bottom of the ablation crater when the laser fluence exceeded the damage threshold of material. A model based on the theory of interference between the incident laser and the surface scattered wave was adopted to explain the formation mechanism of the LIPSS. [ABSTRACT FROM AUTHOR]

• The performance degradation and compensation method of the beam-steering device based on liquid crystal polarization grating (LCPG) and liquid crystal adjustable half-wave plate (LCAHWP) is studied. • This beam-steering device can still work at a laser power density of 16 W/cm2 irradiation. • The laser tolerance of the device is higher than that of liquid crystal optical phased array (LCOPA) and liquid crystal micro-lens array (LCMLA). The effects of laser irradiation thermal deposition on the performance degradation of liquid crystal (LC) devices in high-power laser systems are extremely vital. In this study, the first-order beam-steering system (FBS) was developed using a passive liquid crystal polarization grating (LCPG) and liquid crystal adjustable wave-plate (LCAW). The LCPG was prepared by holographic exposure technology, and the LCAW was prepared using the standard LC cell preparation process. We investigated the influences of diffraction efficiency of FBS under a 1070-nm continuous-wave (CW) laser irradiation. The energy is concentrated in the −1st order at first. When the half-wave retardation was reached, all the energy is concentrated in the +1st order (∼97 %), and the beam is deflected. Once the phase retardation decreases below the half-wave retardation, the energy gradually reconcentrates in the −1st order. When the LCAW fails, the diffraction the energy is refocused to the −1st order by the LCPG. The results indicated that both thermal deposition and driving voltage reduce the phase retardation of the LCAW, generating a variation of energy between in ± 1 st orders. By reducing the driving voltage, this half-wave retardation can be recovered under a certain half-wave voltage and laser power density, and the diffraction efficiency of the +1st order can be compensated to ∼97 %. If the reduced phase retardation is not less than half-wave, the FBS can still be modulated in high-power continuous lasers. Our research provides a reference for the development of beam-steering technology based on LC materials in high-power laser systems. [ABSTRACT FROM AUTHOR]

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]

The laser-induced damage (LID) response of multilayer dielectric gratings (MDGs) to transverse magnetic (TM) and transverse electric polarization was investigated based on polarized-independent MDGs. It was found that TM-polarized MDGs have the superiority of a high LID threshold, low sensitivity to laser excitation strength, low response to damaged structure, and reduced LID growth speed and dynamics. These results provide a strong motive to preferentially develop and mount TM-polarized MDGs in the next generation of high-intensity picosecond-petawatt laser systems. [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]

• 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]

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: When femtosecond laser irradiates materials, plasma with high electronic temperature and low lattice temperature will form due to very high laser power density. This plasma with high electronic temperature cannot exist stably, and it has a trend to expand. If the plasma inclusion is initialized, it will be confined by outer layers when it expands. In this paper, the energy conservation rule was used to analyze the mechanical evolution of inclusion of plasma explosion. An inequality for judging whether the film can be damaged has been deduced. [ABSTRACT FROM AUTHOR]

It is well known that the location of guided-mode resonance (GMR) in grating waveguide structures closely tracks the leaky mode dispersion curves. In this paper, taking Bragg reflection due to periodicity and interaction between different modes into account, we first present a schematic diagram of the dispersion relations of leaky modes in multimode grating waveguide structures, both for s-polarized (TE mode) and p-polarized (TM mode) incident waves. Due to the perturbation of the grating layer, the interaction between different resonance modes (transverse standing waves) is inevitable. This transverse interference will result in the non-Bragg nature resonance band gaps in the dispersion curves. Exploiting the characteristics of leaky mode dispersions over the full range of the first Brillouin zone, we hoped we could gain some insight into the relationship among the mode interactions, band gaps, and their benefits to optical elements utilizing the GMR effect in grating waveguide structures. Finally, a specific structure is analyzed. [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: In experiments, we have found an abnormal relationship between probability of laser induced damage and number density of surface inclusion. From results of X-ray diffraction (XRD) and laser induced damage, we have drawn a conclusion that bulk inclusion plays a key role in damage process. Combining thermo-mechanical damage process and statistics of inclusion density distribution, we have deduced an equation which reflects the relationship between probability of laser induced damage, number density of inclusion, power density of laser pulse, and thickness of films. This model reveals that relationship between critical sizes of the dangerous inclusions (dangerous inclusions refer to the inclusions which can initialize film damage), embedded depth of inclusions, thermal diffusion length and tensile strength of films. This model develops the former work which is the statistics about surface inclusion. [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]

Roles of absorbing defects and structural defects in multilayer under laser radiation were investigated. The HfO2/SiO2 dielectric mirrors for 355 nm were prepared by conventional electron beam deposition. Two kinds of HfO2 with different purity were chosen as the high index material, and impurity content of the materials was accessed by glow discharge mass spectrometer (GDMS) and X-ray photoelectron spectroscopy (XPS). Laser damage testing was performed in both the “1-on-1” and “s-on-1” regime, using 355 nm pulsed laser at a pulse length of 8 ns. It was found that the single-shot laser-induced damage threshold (LIDT) is much higher than that of the multi-shot, and the absorbing defects hindered the improvement of laser damage resistivity greatly in the single-shot process, but in multi-shot mode the main factor influencing LIDT is accumulation of irreversible changes of structural defects. Optical microscopy and surface profiler were employed in mapping laser-induced damage morphology features after irradiation. [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]

Mentions how a Co/Sb multilayer shows the theoretical reflectance of 62% at a photoenergy of 528 eV and the grazing angle of 10.3°. How the measured reflectance is very low, which is considered to result from the low energy resolution of the incidence light; Investigation of the effect of the energy resolution of the incidence light on the measured reflectance; Reference to a new method how to calculate the reflectance of non-monochromatic light; Trend for the calculated data to show that the reflectance of Co/Sb multilayer is very sensitive to the effect of the energy resolution of the incidence light; Findings for it to be very low unless the energy resolution of the incidence light is high enough; Use of a method which gives the fitted result of the reflectance spectrum; Consistency of the fitted result with the measured reflectance spectrum.

Hydrophobic antireflective coating is fabricated by physical vapor deposition. The optical, contact angle and laser damage resistance properties are investigated, respectively. The transmittance of the antireflective coating with hydrophobic layer is 99.58% at 1064 nm with normal incidence. The contact angle with water is 115.6 ∘ . The laser damage threshold of the zero probability is 22 J/cm2 at 1064 nm with the 12 ns pulse width. This new hydrophobic antireflective coating can be applied in the areas of astronomical optics, laser medical equipment and solar energy, etc. [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]

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]

Abstract: ZnO films prepared by the thermal oxidation of the ZnS films through thermal evaporation are reported. The as-deposited ZnS films have transformed to ZnO films completely at 400°C. The 400–700°C annealed films with a preferential c-axis (002) orientation have a hexagonal wurtzite structure. The band gap of ZnO films shifts towards longer wavelength with the increase of the annealing temperature. The relationship between the band gap energy of ZnO films and the grain size is discussed. The shift of the band gap energy can be ascribed to the quantum confinement effect in nanocrystal ZnO films. The photoluminescence spectra of ZnO films show a dominant ultraviolet emission and no deep level or trap state defect emission in the green region. It confirms the absence of interstitial zinc or oxygen vacancies in ZnO films. These results indicate that ZnO film prepared by this simple thermal oxidation method is a promising candidate for optoelectronic devices and UV laser. [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]

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]

[Display omitted] • Femtosecond(fs) laser pretreatment notably increases polishing efficiency of RB-SiC. • The proposed pretreatment method has low requirements for substrate surface profile. • Pre-coated Si powder is oxidized and bonded to the RB-SiC with fs pretreatment. • A high-quality modified layer can be obtained by optimizing the oxidation depth. It is a great technical challenge to precisely and efficiently polish RB-SiC substrates due to their two-phase structure and extreme hardness, especially for large-optics fabrication. Here, a simple laser pretreatment process is demonstrated for improving the polishing efficiency using femtosecond laser to modify the RB-SiC surface pre-coated with silicon powder. Material characterization and finite-element analyses reveal that the pre-coated surface is oxidized under femtosecond laser irradiation. As oxidation gradually penetrates deeper into the interface, the modified layer forms a bonding with the RB-SiC substrate. By optimizing laser scanning parameters to adjust the oxidation depth, a high-quality modified layer with stronger adhesion strength can be obtained. The approach is capable of delivering a modified layer that is easier to polish and tightly bonded to the RB-SiC substrate with an adhesion strength of 55.46 N. Thanks to the femtosecond laser modification, the surface roughness of the pretreated RB-SiC can be reduced to Sq 4.5 nm in just a few hours of polishing, which increases polishing efficiency over 3 times compared with direct abrasive polishing. Low requirements for substrate surface profile and simple operation make this laser pretreatment approach possible to be applied to more complex RB-SiC surfaces and significantly improve polishing efficiency. [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]

Abstract Real-time detection of scattering intensity and the time-resolved imaging technique were combined to reveal the development sequence of laser damage. The real-time detection of scattering intensity can reveal when the damage occurs and grows rapidly, indicated by the increase of scattering intensity during the entire irradiation with picosecond time resolution. Furthermore, the time-resolved imaging technique was applied to observe detailed modifications of the specific moments when the scattering intensity exhibits a sudden increase. Three characteristic moments during a damage event induced by a nanosecond pulse at 355 nm in thick fused silica were captured by the real-time detection of scattering intensity. These three moments were located at the rising edge of the pulse, near the peak of the pulse, and near the end of the pulse. Combined with time-resolved images captured near these three moments, the results indicate that damage of the filamentary tail appeared at the rising edge of the pulse. Further, the head region of the filamentary damage developed near the peak of the pulse. The whole damaged area grew rapidly near the end of the pulse. The underlying physical mechanisms around the three characteristic moments are discussed to interpret the development sequence of laser damage. [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]

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]