This PDF file contains the front matter associated with SPIE Proceedings Volume 12982, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

The pulse compressor has evolved to be a core module of 100 Petawatt (PW) or Exawatt laser facilities; however, the diffraction efficiency bandwidth, laser-induced damage threshold (LIDT), and aperture of its currently deployed gratings strongly restrict the ultra-intense and ultrashort pulse compression. Maximizing the energy-loading capability of gratings is a worldwide challenge in the high-peak-power laser field. Here, for 10’s femtosecond-PW pulse compression, an ultra-broadband gold grating was developed to dramatically broaden the high diffraction efficiency bandwidth from 100–200 nm to 400 nm. Moreover, a core mechanism was elucidated whereby the high diffraction efficiency combined with the deep penetration effect of electrons under high-energy laser irradiation can tap the LIDT potential of metal grating. Accordingly, the mixed metal grating was invented and demonstrated experimentally with superior performance in terms of diffraction efficiency bandwidth and LIDT compared with normal gold gratings. In addition, for picosecond-PW pulse compression, a multilayer dielectric grating (MDG) design paradigm was proposed. Importantly, TM-polarized MDGs had the superiority of a high LIDT owing to the low electric field intensity. Furthermore, a novel grating with a LIDT 3.5 times higher than the conventional gratings installed in NIF-ARC and SG-II was obtained by taking advantage of TM polarization and a small incident angle. These results make a pioneering technical reserve to facilitate future 100 PW-class ultrafast laser systems.

Multilayer Dielectric Gratings (MLDGs) are the core optics of the picosecond-petawatt laser systems based on Chirped Pulse Amplification (CPA). The MLDGs encounter nanosecond- and picosecond-laser irradiation during the broadening and recompression of the laser pulse in CPA. Therefore, a comprehensive evaluation of the laser-induced damage performance of MLDG in the nanosecond (ns) and picosecond (ps) regimes is required. Herein, we examined the laser damage characteristics of MLDGs induced by the 8-ns and 8.6-ps laser pulses. In the two tested laser pulse widths, the damage of the MLDG was dominated by the nano absorbing defects and nodular defects, but the damage mechanism has changed. When the laser pulse width is shortened from ns to ps, the damage sites caused by the absorbing defects transfer from the interface to the grating pillars, where there is the maximum electric field. And the nodular ejection pit changes from a complete eruption to a local damage corresponding to the electric field enhancement region. For the nodular defects, ns-laser conditioning was introduced for removing them and achieved a maximum enhancement of 40% in the ps laser-induced damage threshold.

For the contaminated large-aperture vacuum separator coated with SiO2 sol-gel antireflection film in the facility, a Nd: YAG pulsed laser with a wavelength of 355 nm was performed in laser cleaning experiment. The experiment adopted a single-shot laser dry cleaning and a laser cleaning system assisted by an airflow replacement system. The experimental results suggest that there is an optimal process window for laser in-situ cleaning of optics. The optimal laser energy density for dry laser cleaning is 1.71 J/cm², and the total particle removal rate is 57.67%. After using the airflow assisted laser cleaning process, the total particle removal rate is increased to 82.21%, which is improved by 24.54%, and it can effectively achieve complete removal of particles over 5 μm in diameter. Additionally, the optical microscope analysis results show that adding an airflow displacement system will not affect the substrate laser damage threshold. The result indicates that the airflow displacement assisted laser cleaning can effectively improve its cleaning effect and reduce the particle re-adhesion.

The deleterious effects of organic contaminants on optical components are a major obstacle to high-energy laser systems, and laser ablation is an important means of removing contaminants. Nevertheless, irregularities or flaws created during the manufacturing process of optical element surfaces affect the absorption of organic contaminants while placing higher demands on laser ablation. Hence, it is imperative to comprehend the intricate interplay among surface roughness, contaminant absorption, and ablation in order to effectively confront the challenge of laser-induced damage. In this study, the three-dimensional morphology of the fused silica surface was simulated numerically employing the Weierstrass-Mandelbrot fractal function. On this basis, we developed a theoretical model through molecular dynamics simulations to gain insight into the adsorption process of dodecane organic molecules on fused silica surfaces. Building upon the obtained outcomes, the effect of surface roughness on the laser removal of the adsorbed model is comprehensively analyzed. The findings reveal that dodecane molecules tend to aggregate within enclosed crevices and irregular regions, resulting in heightened localized density. Additionally, an augmented substrate surface roughness diminishes van der Waals energy and pressure, thereby facilitating the elimination of contaminants. These findings are indispensable for deepening our understanding of the dynamic interactions involving lasers, fused silica, and organic contaminants, as well as providing valuable insights into effectively addressing the challenging issue of laser-induced damage.

Fused silica is an important optical material used in scientific research, industry and medical fields. In order to explore the mechanism of femtosecond laser damage in fused silica, a multi-physics coupling dynamics model was developed to obtain the transient dynamic behaviors of laser damage. It is found that the thermal wave and mechanical wave caused by initial energy deposition plays an important role in the crack formation near the laser irradiation area. The simulated evolution of laser damage is verified by the early transient images captured by the ultra-fast experimental detection system. This work provides further insights in explaining the laser-induced damage in fused silica.

Particle contaminant-induced laser damage of optical components limits the outpower of high-power laser facility. Fused silica particles from damaged fused silica optical components can cause laser damage to optical elements. In this article, the influence of fused silica particles on fused silica surfaces is investigated. The Maxwell equation and free electron production rate equation are coupled. The results show that although the particles create an electric field-enhancing effect inside the component, the particles are still the first to be damaged because their free electron density is greater than the free electron density of the substrate. When the laser is incident forward, the peak of the free electron density curve of the particle and the substrate is proportional to the particle size. On the contrary, When the laser is incident from the back, as the particle size increases, the peak value of the free electron density curve first increases and then decreases. The shortening of the separation distance between particles significantly increases the free electron density inside the substrate.

Increases in the laser damage threshold of fused silica have been driven by the successive elimination of near-surface damage precursors such as polishing residue, fractures, and metal ions. In this work, we show that trace impurities used to process fused silica optics may be responsible for the formation of carbonaceous deposits. Firstly we use surrogate materials such as sugar, potassium hydrogen phthalate, medical Vaseline to show that organic compounds precipitated onto fused silica surfaces form discrete damage precursors. Secondly, we test the impact of these organic compounds on the damage threshold and conduct cleaning and removal experiments on these organic compounds. By cleaning, etching, and other treatment processes, the suppression of most organic pollutants is achieved. Finally, the control effect of organic pollutants is verified through damage testing.

In high-power laser systems, hot image is a phenomenon of drastic intensification on the downstream light field due to nonlinear Kerr self-focusing, which poses a threat to the safety of optical components. It is traditionally believed that a single defect will trigger a hot image, which appears at the downstream conjugate position of the defect relative to the nonlinear medium. Our previous study has shown that a phase defect can cause double-peak hot images when considering the defect edge steepness. When the number of defects increases, the downstream modulation becomes more complex. Here the evolution of the hot-image is analyzed when there are two symmetrical distributed super-Gaussian defects around the beam center for example. The results show that double defects will form five modulation peaks. The second and fourth peaks are the results of two single defects. Another three peaks are in the center of the beam, which do not appear in the case of single defect. The linear modulation peak is generated by the interaction of diffraction fringes from double defects and finally forms the first peak. The second and third strong peaks are caused by the interference between the second and fourth peaks, respectively. The characteristics of these three peaks are affected by the center spacing and size. The existence of these new strong modulation regions will pose a potential damage threat to the optical components at this position, so they need to be avoided when designing the arrangement of the components.

Time-resolved pump-probe technology is an effective method to study the dynamic damage process of optics. In this paper, the dynamic damage process of HfO₂/SiO₂ anti-reflection coating, for the cases that the coating located on the laser incidence (forward process) and exit (reverse process) surface, irradiated by a 1064nm nanosecond laser was studied based on the time-resolved pump-probe technology of intensified charge-coupled device (ICCD). Under the irradiation of the same fluence (52J/cm²), pits without and with the layer peeling existed in both forward and reverse processes. However, the lateral size and depth of the small pits generated by the reverse process are larger than those of the forward process. The finite element analysis shows that the electric field intensity (EFI) on the substrate-coating interface for the forward and reverse processes is similar, which is not enough to form the difference in damage morphology. These results indicate the develop process of the plasma after its formation under the subsequent laser pulse irradiation determines the damage difference in the above two cases. The time-resolved study of anti-reflective coating damage is of great significance for its damage mechanism analysis and practical application.

Fused silica optics are widely used in high-power laser systems and ultraviolet optical systems because of their excellent properties. Laser-induced damage threshold (LIDT) of fused silica is a key problem that limits the improvement of optical systems. Atmospheric pressure plasma processing (APPP) has great promise for improving LIDT because it involves lowcost, non-contact, and high-efficiency material removal based on its pure chemical etching mechanism. However, the deteriorated surface morphology after atmospheric plasma etching limits the further improvement of LIDT of fused silica. This study analyzes the exposure and passivation processes of subsurface scratches during atmospheric pressure plasma processing. The evolution process of interfacial contours related to the etching and deposition process is described. At the end, a series of etching experiments under different dwell times are carried out and a flexible medium polishing processing is used to improve the deteriorated surface quality. The results indicate that the LIDT of fused silica is significantly increased from 8.1 J/cm² to 30.8 J/cm² by APPP and flexible medium polishing processing. APPP is expected to be effective in improving the LIDT of fused silica.

Plasma has been widely used in the in situ removal of organic contaminants on the surface of large aperture optical components by physical bombardment and chemical reaction. Since the plasma is usually generated by ionizing gas through the electric field, the charged reactive species are accelerated to bombard the surface when passing through the surface sheath. After the organic contaminants on the surface of the optical components are completely removed, the surface film of the optical components may be eroded by long-time plasma irradiation. Therefore, the surface damage characteristics induced by plasma cleaning on optical components were studied to apply the technology of plasma in situ cleaning in the inertial confinement fusion facilities. Firstly, the effect of the amount of organic contaminants on the performance of optical components was investigated. Then, the influence of plasma cleaning time on the transmittance and wavelength peak of fused quartz optical components coated with sol-gel anti-reflection film was analyzed. The plasma cleaning experiments illustrated that the film thickness had a damage accumulation effect after the long plasma irradiation, and the surface pores gradually increased. The surface damage mechanism of plasma action was discussed. Finally, the research on the surface damage mechanism of sol-gel anti-reflective film during plasma cleaning lays a foundation for the realization of nondestructive in situ cleaning of optical components.

Plating metal grids on the surface of infrared optical materials can effectively enhance its electromagnetic shielding performance. In this research, fused silica optics were plated with different configurations design (with a duty cycle of 5.5%) of Au-based metal grids, and the light-field distribution and light transmittance of fused silica were simulated as well as the temperature testing was carried out. The results show that the metal grids configuration has marginal effect on the light field intensity, since the Au-based grids with the duty cycle of 5.5% make Light Intensification Factor (LIF) remain constant at 2.95 regardless of its linewidth and period. But the occurrence probability of maximum electric/light field is increased when increasing the linewidth of metal grid, indicating that wider grid has no benefit the light modulation substrates. The metal grids in 6 μm linewidth deteriorates the infrared window transmittance by 3.48%. When exposure upon continuous infrared laser, the temperature of sample increases with illumination time. And the most significant temperature rise was observed for the metal grid configuration with a linewidth of 10 μm and a period of 359 μm, reaching as high as 390.75 K when irradiated for 60 s.

Polyimide films have high strength, low density, excellent thermal stability, good insulating properties, excellent UV stability and infrared transmittance, and are widely used in thermal control structures on spacecraft, solar arrays and other components, as well as solar sails and other inflatable deployment structures, and the commonly used films include aluminized polyimide films, antistatic aluminized polyimide films, germanium plating polyimide films, and carburized black polyimide films, etc. Due to long-term exposure to the various space environments, their properties will be seriously degraded, such as thermo-optical properties, electrical properties, and mechanical properties. In this paper, for the application of polyimide film in spacecraft, we analyze the application performance requirements, introduce the influence of space environment on film materials. For these above materials, the results of the study of the degradation of the performance of these polyimide films under the action of space particle radiation, solar ultraviolet radiation, atomic oxygen and other environments were presented.

With the continuous development of optoelectronics science, the widespread and intensive application of transparent optical elements has become an indispensable condition for the development of information technology in society. Transparent optical elements under the action of strong laser light are prone to produce plasma and even then cause damage to the elements. Therefore, it is important to study the process of interaction between transparent optical elements and strong laser light and its results. In this paper, a theoretical research and simulation study is conducted to investigate the characteristics of pulsed laser induced plasma generation in transparent optical elements represented by fused silica. It is demonstrated that the plasma propagation velocity and the temperature of each part increase with the increase of laser energy density during the interaction between the pulsed laser and the transparent optical elements. The plasma propagation velocity tends to increase and then decrease with the increasing of laser action time, and the temperature continues to increase near the threshold value. The plasma propagation velocity increases with the increasing of laser pulse width, and the velocity variation pattern is similar in all pulse widths. The temperature increases with the increasing of laser pulse width and approaches the temperature threshold that can be reached by the combustion wave generated by the interaction between the pulsed laser and fused silica. Finally, the kinetic characteristics and temperature rise phenomenon of the plasma propagation generated during the interaction between the pulsed laser and the transparent optical element are explained.

Traditional potassium dideuterium phosphate (DKDP) polishing techniques, such as single-point diamond flycutting (SPDF), magnetorheological polishing (MRF), and ion beam computation (IBF), are prone to edge collapse, subsurface damage, and small removal rates. In the study, the mechanism of crystal deliquescence is investigated based on the nature of DKDP crystal that are susceptible to deliquescence, and a method of water dissolution ultra-precision continuous polishing of DKDP crystal is proposed, with the corresponding water-in-oil solution configured as a polishing solution. The polishing solution proposed in the paper includes nonylphenol polyoxyethylene ether as a surfactant, glycerol monooleate as an oil phase, n-octanol as a cosurfactant, and pure water as an aqueous phase. The water nucleus in the polishing solution is squeezed, rubbed, and then deformed and ruptured by the action of the polishing pad and the rough peaks on the surface of the DKDP crystal, and the water molecules inside the ruptured water nucleus flow out and dissolve the surface of the crystal, resulting in the polishing of the DKDP crystal. The experimental results show that the water dissolution ultra-precision continuous polishing method can well alleviate the problems of subsurface damage and small removal rate of DKDP crystal brought by the conventional processing. DKDP crystal have surface roughness (Ra) of less than 12 nm and face shape accuracy (RMS) of less than 15 nm.

Reflective Volume Bragg Grating (RBG) recorded in photo-thermo-refractive glass offers notable advantages, including high efficiency, narrow bandwidth, and multiplexing capabilities, making them ideal for applications in dense wavelength division multiplexing (DWDM) and demultiplexing. However, the side lobes caused by sudden changes in coupling strength at both ends of the grating always lead to interchannel interference, which evidently affects the effectiveness of multiplexing and demultiplexing. In this work, a theoretical model of the apodization for RBG, which based on Kogelnik's coupled wave theory and F-matrix theory. It is simulated and analyzed the effects of three apodization functions including cosine, gaussian, and hyperbolic secant functions is established. The simulation results indicate that the side lobes of the RBG with apodization is significantly reduced and the peak efficiency is determined by the total refractive index modulation. This work provides a theoretical design basis and parameters optimizing method for the development of apodized RBG.

Aluminum (Al)-based metal-dielectric composite coatings play a crucial role in the production of vacuum ultraviolet (VUV) optical components and laser systems. In the short-wavelength range of the VUV region, there is a high demand for practical Al-based coatings with high reflectivity, which imposes strict requirements on the preparation process. Key parameters of the preparation process, such as deposition rate, film thickness, and deposition temperature, significantly influence the growth and short-wavelength VUV optical properties of the coatings. In this study, we utilized electron-beam evaporation technology to prepare magnesium fluoride (MgF₂) protected Al coatings for short-wavelength VUV reflection. We explored the impact of the aforementioned key process factors on the coatings’ properties and improved the reflectivity of the coatings in the short-wavelength VUV range, achieving reflectivity above 85% at the wavelength of 121.6 nm.

In view of the application requirements of optical elements with some incident angle in laser-related products, laser damage measurement were carried out on 1064nm anti-reflection films with an incident angle of 45° deposited with the commonly used film materials combination HfO₂-SiO₂ and film materials combination ZrO₂-MgF₂, and the resistance of laser induced damage of the two samples was compared. Two groups of experiments prepared with different film materials were carried out in evaporation coating equipment equipped vacuum pump without oil. Then we designed the film structure, formulated the process plan and got the sample respectively. LIDT of two samples were measured, and the results were analyzed and compared. The results show that the film deposited by the film materials combination ZrO₂-MgF₂ performed well when the process conditions were suitable for the materials. And the resistance of laser induced damage performed similar to the film materials combination HfO₂-SiO₂ under similar process conditions. The research about material ZrO₂-MgF₂ may be strengthened in the future.

The research investigated the light modulation of Hertzian microcracks on K9 optical glass with SiO2 thin film by simulations. The simulations considered parameters such as crack degree, crack opening width, and crack depth. It was observed that the internal light intensity is positively correlated with the crack degree of the microcrack. At a crack degree of 55°, the peak of light intensity occurs at the thin film, indicating that the film layer may be damaged earlier by the laser. Laser damage may first occur in the thin film with a small opening width (<0.6 μm), and as the opening width increases, damage may occur inside the substrate of the optical element. Peak points of light intensity appeared inside the thin film and substrate at a crack depth of 1 μm, and as the depth increased, the substrate became more susceptible to laser damage.

In reverse Hartmann measurement, the display often undergoes thermal deformation due to self-heating, which can cause drift of pixels on the screen and cause errors in the measurement results. A multilayer LCD model was established based on a linear elastic material model, and the influence of thermal deformation of the display on measurement results was analyzed under different backlighting modes. The results show that when uniformly heated, the PV value increases by 40 nm for each degree of temperature increase in the display, and the main surface errors are tilt and astigmatism under different temperature fields.

Vanadium dioxide is one of the reversible phase transition materials, which can be induced by temperature, electric field, laser, stress, etc. This characteristic makes thin films have great potential applications in fields of various optoelectronic devices. For electro-optical switch applications, a high extinction ratio and low threshold voltage are required, which are closely related to the VO₂ film thickness. In this paper, VO₂ thin films with different thicknesses were deposited on ITO substrates by pulsed magnetron sputtering. Microstructure, optical and electrical properties, and phase transition performance of the samples are investigated. The research results have a high reference value for the design of high-performance VO₂-based electro-optic switches.

Meter-scale optical films have become core components in large-size optical systems. Improving film thickness uniformity is a crucial issue to ensure optical properties. Ag films are commonly used as high-reflection mirrors for optical systems. Here a meter-scale magnetron sputtering equipment has been independently developed for coating Ag films. Two strategies were performed to correct the film thickness uniformity in the horizontal direction and vertical directions respectively. Specifically, the film thickness uniformity at the horizontal position was guaranteed by scanning the target parallel to the horizontal direction. Meanwhile, a mask was designed to optimize vertical film thickness uniformity. The film thickness, fitted by X-ray reflectometry (XRR), non-uniformity is less than 3% both in the 1800 mm range of the horizontal direction and the 1100 mm range of the vertical direction. This study has brought new insight into the development of meter-scale thin film optics.

With the increasing scope of applications of laser, it is crucial to study the pollution of optical components for regulating beams in intricate environments. In resonance ionization spectroscopy instruments, the optics may suffer from contamination caused by both the analyzed sample and environmental impurities, which can cause detrimental effects on their optical properties, potentially leading to their degradation or destruction. The paper analyses the spectral performance of two categories of reflective mirrors that have been exposed to four kinds of contamination (Nd, Nd-oxide, Fe, and C) for comparison of reflectance degradation process variations. It is found that the impact of multiple contaminant components on the spectral performance of reflective mirrors is directly linked to their light transmission characteristics, with metal contamination in particular causing the most severe degradation.

Some key issues in the process of simulating millisecond laser damage to K₉ glass based on Multiphysics field simulation are analyzed through several aspects such as the establishment and meshing of the millisecond laser damage K₉ glass finite element model, loading of the pulsed laser, setting the initial conditions and boundary conditions. The finite element model of K₉ glass damaged by millisecond laser was established, and the temperature and stress distribution of K₉ glass irradiated by millisecond laser were numerically analyzed. The calculation results show that the spot radius and pulse frequency have a greater influence on the damage effect, the higher the frequency, the greater the thermal stress generated, and the stronger the damage effect; the larger the laser spot radius, the smaller the thermal stress generated, and the weaker the damage effect. Therefore, the laser damage threshold will be the spot radius, the pulse frequency of the regular change, that is, with the pulse frequency and spot radius increases, the damage threshold decreases.

Polyimide film can be used in spacecraft thermal control multilayer and large-scale deployment structure, and its mechanical properties will be degraded by space radiation environments such as electron and proton. In this paper, the mechanical properties of polyimide film under the synergistic effect of electron and proton was studied using the space integrated irradiation test facility in Beijing Institute of Spacecraft Environment Engineering. It is found that the combined irradiation of electron and proton damages the polyimide film more than the single environment of electron or proton. The synergistic effect of electron and proton causes the exponentially decrease of rupture elongation and the tensile strength of the polyimide film with. With the increase of the electron and proton irradiation fluence until its properties reaches a steady state.

Bulk water is one of the important transparent medium for laser applications. Its laser-induced breakdown threshold (LIBT) is of special value for the understanding of laser propagation and laser-induced damage. And it is also very important for laser applications such as laser-induced plasma spectroscopy. To further research the influence of water quality on the breakdown threshold, the breakdown of water and salt solution by nanosecond laser pulse irradiation was investigated in this work. It was found that the LIBT of solution decreased significantly with the increase of zinc acetate concentration, while the LIBT of pure water remained 1.705×10¹² W/cm². There is a linear correlation between zinc ion concentration and laser breakdown threshold. The difference between water and salt solution may suggest that impurities play an important role in laser damage in transparent media. The result provides a guidance for the understanding of the mechanism of laser damage for optically transparent media and LIBS application to detect metal ion in solution.

Polyimide film had been widely used on the spacecraft as thermal control material or structural materials. During in mission, polyimide film will be damaged by space radiation environments such as energetic charged particles and solar electromagnetic radiation, especially electron, proton and ultraviolet, which will lead to the degradation of its mechanical properties or structural rupture. In this paper, the mechanical properties of polyimide film under the synergistic effect of electron, proton and near ultraviolet was tested by the space integrated irradiation test facility in Beijing Institute of Spacecraft Environment Engineering, and the tensile strength and rupture elongation of it was studied. Under the synergistic effect of ultraviolet, electron and proton, the mechanical properties decrease in the early stage of irradiation larger than in the electron and proton irradiation, but less than in the degradation of mechanical properties caused by electrons and protons in the later stage of irradiation. During the initial stage of synergistic irradiation of electron, proton and near ultraviolet, the degradation law of mechanical properties of polyimide films is basically consistent with that under electron or proton irradiation. But its tensile strength and rupture elongation will exponentially increase with space combined radiation until tend to stable.

The laser damage characteristics of the thin-film polarizers for the wavelength of 532 nm and AOI of 56° were investigated using a Nd:YAG laser system with a wavelength of 532 nm and a pulse width of 9 ns. The results showed that the damage morphologies induced by nodular defects in the witnesses is significantly different compared to 1064 nm polarizers. The nodular seeds are incompletely ejected after on-shot laser and butterfly-like damage pits are formed, which gradually develop into the typical nodular ejection pits as laser irradiation. Analysis of the internal structure showed that single or two adjacent SiO₂ particles formed the nodular seeds, which were mainly located in bottom layers and were tightly bound to the surrounding layers. In addition, the simulated electric field intensity (EFI) distributions and damage morphologies of nodular defects with different structures were compared, and it was found that the formation of the nodular damage is closely related with the EFI distributions in the thin films.

13.5nm femtosecond laser induced damage behaviors of Mo/Si multilayer were investigated. In this repo rt, we designed and prepared the Mo/Si mirrors for high reflectivity at 20 degrees. The laser damage test for EUV femtosecond pulses was executed at domestic soft x-ray free-electron laser facility in Shanghai. The EUV central wavelength is 13.5 nm and pulse duration is 300 fs. To understand the influence of absorption distribution in the Mo/Si multilayers, the sample was irradiated at normal incident angle for no reflection status. The damage morphologies were characterized by SEM and TEM. It is found that the most severe absorption area appears bubble-like damage, in which the first ten pairs of Mo/Si bilayer merged thoroughly and the bubble under the multilayers is located at the interface close to the substrate. The absorption distribution in the multilayers was simulated by Monto Carlo method, and that was compared with the electric field distribution simulation. We can conclude from the simulation that the damage locations are consistent with the high absorption layers in the coating stacks.

Laser continuous/dispersed quenching techniques were used for surface hardening Cr8 cold work die steel, and its metallographic microstructures and mechanical properties are investigated in this work. Typical mixed structure which composed of carbides in different morphologies and acicular martensite can be obtained by laser quenching. The excellent wear resistance and surface hardness of Cr8 die steel are attributed to the synergistic effect of solid solution strengthening, grain refinement and high dislocation density. Meanwhile, the phase change hardening layer structure and residual tensile stress induced by full area coverage scanning (LCQ) are the main factors to deteriorate the impact toughness and bending performance after laser quenching. The soft substrate-hardened unit structure with laterally spaced distribution (LDQ) obtained by graphical scanning reduces the heat accumulation effect on the surface, which reduces concentration of deformation near the hardened layer. The bending property and fracture mechanism are studied. Compared with the forging die material treated by LCQ, the impact energy and bending resistances of forging die materials treated by LDQ are enhanced significantly. Consequently, Cr8 die steel takes into account the same wear resistance, and scanning strategy should be controlled to retain more interval distribution hardening units in layer structure for superior impact toughness and bending properties.

Progress report is made on the development of a multimodal inspection technique for surface/sub-surface defect characterizations of large-aperture optics. A high-speed laser scattering imaging with a sensitivity at 200-nm scale is used for defect discovery of large-aperture optics. The defect discovery provides statistical results of defects of the optics. After that, a multifunctional microscopic method is used for local defect review. A photothermal scanning microscopy is used for specific characterization of absorption defects, and a confocal microscopy is used for characterization of sub-surface defects. The defect review provides information for defect classification. Based on this multimodal technique, an inspection system is also developed and used for defect characterizations of large optics. Data analysis of the output of the system offers insight into the quality control process. In addition, a absorption distribution curve method is also proposed, which provides a new vision for evaluating the quality of large-aperture optics.

Tm³+/Yb³+ co-doped germanate-tellurite glasses were prepared by high temperature melting with components of 50GeO₂-20TeO₂-25Na₂O-3Ga₂O₃-2Nb₂O₅-2Yb₂O₃-xTm₂O₃ (x = 0.25, 0.5, 1, 1.5, 2 mol%). According to the absorption spectrum and J-O theory, the spectral line intensity parameters (Ω2, Ω4 and Ω6) of Tm³+ ions and the spectral parameters of each excitation energy level transition were calculated. Under the excitation of 980 nm LD, the up-conversion and down-conversion emission spectrum of glasses at different concentrations of Tm³+ ions were measured with the emission wavelengths at 478, 651, 808 ,1484, and 1937nm respectively, and the concentration quenching of each luminescence was found, the up-conversion emission intensity was maximum at the doping concentration of 0.1mol%, and the concentration quenching of Tm³+ ions was analyzed. Furthermore, the optical temperature sensing properties was investigated based on the ³F₂ and ³H₄ levels of Tm³+ ions.