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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]

Laser damage of fused silica is a critical problem that limits the fluence increase of high-power laser systems. The reaction of plasma processing of fused silica was analyzed. The redeposited layer was removed and scratches of the fused silica were passivated by plasma to increase the laser-induced damage threshold (LIDT). It was found that the deposition generated during the etching process adheres to the surface of fused silica to limit the further increase in the LIDT. The LIDT of fused silica tends to increase and then decrease as fused silica is processed by atmospheric pressure plasma. Accordingly, a competitive evolution for etching and deposition affecting the LIDT of fused silica was established. The etching and deposition relationship analyzed by the model can effectively increase the LIDT of fused silica without deteriorating the original surface of fused silica by choosing an appropriate dwell time. [ABSTRACT FROM AUTHOR]

Low dispersion mirrors are important because of their potential use in petawatt (PW) laser systems. The following two methods are known to increase the laser-induced damage threshold of low dispersion optical components: use of a wide-bandgap-material protective layer and control of electric field distribution. By controlling the electric field distribution of composite low-dispersion mirrors (CLDM), we shift the electric field peaks from the material interface into the wide-bandgap material. However, the damage threshold of modified-electric-field composite low dispersion mirror (E-CLDM) does not increase. Damage morphology shows that the initial damaged layer is Ta2O5. An immediate cause is the enhancement of the electric field in internal layers caused by surface electric field regulation. Theoretical calculations show that the damage threshold of CLDM or E-CLDM is determined by the competition results of bandgap and the electric field of layer materials. The CLDM with different materials or different protective layer periods can be optimally designed according to the electric field competition effect in the future. [ABSTRACT FROM AUTHOR]

Rapid growth processing of KDP crystals was improved by employing continuous filtration to eliminate bulk defects. The performances of the KDP crystals, including scattering defects, laser damage resistance and transmittance, were measured and analyzed. Compared with rapid-grown KDP without continuous filtration, the transmittance in the near-infrared was increased by at least 2%, almost all of ‘micron size’ defects were eliminated and ‘sub-micron size’ defects were decreased by approximately 90%. Laser damage testing revealed that the laser-induced damage thresholds (LIDTs), as well as the consistency of the LIDTs from sample to sample, were improved greatly. Moreover, it identified that ‘micron size’ defects were the precursors which initiated laser damage at relative lower laser fluence (4–6 J cm−2), and there was a lower correlation between smaller size scattering defects and laser damage initiation. The improved consistency in the LIDTs, attributed to elimination of ‘micron size’ defects, and LIDT enhancement originated from the decreased absorption of the KDP crystals. [ABSTRACT FROM AUTHOR]

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

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

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

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]

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]

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

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

As important part of components for 193 nm lithography, AlF 3 coatings deposited by resistive heating method acquire advantages like lower optical loss and higher laser damage threshold, but they also possess some disadvantages like worse stability, which is what aging effect focuses on. AlF 3 single-layer coatings were deposited; optical property, surface morphology and roughness, and composition were characterized in different periods. Owing to aging effect, refractive index and extinction coefficient increased; larger and larger roughness caused more and more scattering loss, which was in the same order with absorption at 193.4 nm and part of optical loss; from composition analysis, proportional substitution of AlF 3 by alumina may account for changes in refractive index as well as absorption. [ABSTRACT FROM AUTHOR]

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

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

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

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]

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]

The laser-induced damage characteristics and adsorption effects of organic contamination molecules of two high reflectors (HR) prepared by electron beam evaporation (EB) and ion beam sputtering (IBS) method at 1064 nm is investigated in vacuum. It is found that EB films show the performance degradation of laser induced damages in vacuum while for IBS film, seems to have no this effect, in comparison with air environment. In addition, EB coatings also have the strong affinity with organic contamination molecules, in contrast of IBS films. The results reveal that ion beam sputtering (IBS) method seem to be one of the favorite film deposition techniques of the optical films used in vacuum and space environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multi-pulse LIDTs of GCPG at different high repetition rates are presented. • A new incubation expression is proposed to analyze the LIDT results. • The expression suits various materials in the field of laser-matter interaction. • Two different types of surface damage morphologies are characterized and compared. • Two types of damage are related to interfacial pyrolysis and adhesion strength. The gold-coated photoresist grating (GCPG) compressor is a core module of the high-repetition-rate superintense ultrafast lasers. Understanding how pulse trains with different repetition rates lead to laser-induced damage of GCPG is critical for future high-power laser applications. In this paper, we present the results of a multi-pulse laser-induced damage threshold (LIDT) investigation of GCPGs at different high repetition rates for the first time. The upper and lower endurance limits of S-on-1 beam-normal LIDT at 50–1000 Hz (800 nm, 35 fs) are ∼0.40 J/cm2 and 0.01 J/cm2, respectively, and the multi-pulse LIDT at 100 kHz is ∼0.02 J/cm2 corresponding to the peak intensity ∼64 GW/cm2 (1030 nm, 320 fs). The typical damage morphologies at 50–1000 Hz that the gold coating strips from the photoresist grating mask differ from those initiated from the expansion of the mask at 100 kHz. Focused ion beam scanning electron microscopy measurements show that the corners and small adhesion strength of interfaces are structural weaknesses. Moreover, theoretical modeling indicates that the differences mainly arise from pyrolysis and low heat-conduction of the mask. Overall, these results are highly practical and lay the foundation for the safe construction of high-repetition-rate ultra-high-power lasers based on the GCPG compressor. [ABSTRACT FROM AUTHOR]

Fig.1. (a) SEM images of the fabricated low-oscillation dispersion mirrors (LODM). The surface GLAD SiO 2 layer has an ultra-low refractive index of 1.09, which is used to reduce the partial reflection of the surface layer, thereby reducing the dispersion oscillation of the entire mirror. (b) electric field intensity(EFI) distribution of three mirrors. (c) multi-wavelength Dynamic EFI distribution of LODM. In Brief. The dispersion oscillation and damage threshold of a dispersion mirror (DM) are the key influencing factors for high-quality pulses and outputting high power density. The sculptured structure film prepared by the glance-angle deposition(GLAD) technique has a porous structure, and its shape and porosity can be adjusted. In this study, we fabricated a low-oscillation DM (LODM) with a high damage threshold through a sculptured structure layer. Although the static electric field intensity (EFI) inside the LODM is 8.5 times that of the Bragg mirror, their thresholds are still close. As laser damage is a dynamic process, EFI is redistributed in time. A new EFI analysis model, which combines the influence of action time and different frequency components is employed. As a result, the EFI transfer to deep due to sculptured layer is the root cause of high damage threshold. In the depth of the film, there is a time difference in the formation of EFI peaks of different frequencies, which causes the EFI in the depth of the film to cancel out. The dynamic effect of few-cycle laser pulses or attosecond pulses damage will be more common. It can elucidate the ultrafast laser damage behavior of film components. [Display omitted] • A low-oscillation dispersion mirror (LODM) with a high damage threshold is fabricated through a sculptured structure layer; • A new electric field analysis model including time component is established to analyze ultrafast laser damage; • Introducing the standing wave field peak of the multilayer into the depth of the film may be a good way to increase the damage threshold. The dispersion oscillation and damage threshold of a dispersive mirror (DM) are the key influencing factors for high-quality pulses and outputting high power density. Here, we studied the femtosecond damage behavior of low-oscillation DMs(LODM) with SiO 2 sculptured layer. The monochromatic standing wave field(SWF) distribution widely used in ultrafast laser damage analysis is sufficient in Bragg mirror. In more complex systems, the actual electric field intensity(typically smaller) will dynamically change due to the broad bandwidth and the time difference of pulse propagation. Time-domain dynamic electric field intensity displays that the spatio-temporal evolution of the pulse within the stacks averages the electric field intensity, especially the electric field in the deeper layers. The dynamic effect of few-cycle pulses or attosecond pulses damage will be more meaningful. The time-domain dynamic electric field model can elucidate the ultrafast laser damage behavior. Introducing the time-domain dynamic electric model into the merit function can help us design optical coatings with high damage thresholds. [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]

• Three-dimensional spatially and temporally resolved method for accurate defect damage thresholds of optical films. • Defects on substrate are significant sources of splitter film damages. • Defect damage threshold of 532 nm laser decreases continuously with 1064 nm laser fluence increases. In this paper, we propose a three-dimensional spatially and temporally resolved method for measuring laser-induced damage fluence by identifying the time onset of defect damage and the damage location in the three-dimensional coordinate system of a Gaussian beam. When considering a second-harmonic beam splitter as an example, the defect fluence of fundamental wave (1064 nm) and second harmonic wave (532 nm) simultaneous irradiation is captured accurately by the proposed method. The defect damage threshold of a second-harmonic beam splitter and the coupling effect between multi-wavelength lasers during defect damage initiation are investigated. Our test method can not only identify complex multi-wavelength laser coupling damage mechanisms that traditional test methods cannot observe, but also provides a new method for obtaining accurate defect information for optical films, which is helpful for improving the laser resistance ability of optical films. [ABSTRACT FROM AUTHOR]

The gold pulse compression gratings (PCG) used in the Bidirectional Grating Compressor (BGC) suffers a nano- and femtosecond dual pulses irradiation. In the case that the ns pre-pulse comes 10 nanoseconds early before the fs pulse, experiments were conducted to investigate damage behaviors under the dual pulse irradiation. 1-on-1 laser induced damage threshold (LIDT) of the ns–fs dual pulses and fs single pulse were tested and compared. Scanning Electron Microscope (SEM) was employed to capture damage onset and exam the damage macro- and micro-morphologies. The mono-shot method, comparison between the damage zone and spatial distribution of laser pulses, was employed to analyze the difference of the damage onset fluences for the two cases thoroughly. It was found that there is no degradation of laser damage resistance due to the ns pre-pulse. Instead, a slightly increase (∼ 10%) of fs LIDT caused by the ns pre-pulse was found. [ABSTRACT FROM AUTHOR]