It is important to understand the damage process of optical coatings subjected to nanosecond laser ablation. However, investigating the high power laser interaction with optical coatings in a short time and space resolution is challenging. The dynamic evolution of materials ejection and layer peeling-off processes during damage of HfO2/SiO2-based anti-reflection coatings induced by 1064 nm pulsed laser were systematically examined by employing the time-resolved shadowgraph technique. Therefore, materials response imaging was performed by shadowgraphy to better understand the interaction between coatings and laser beam in air and vacuum con-ditions. The coatings damage in vacuum was not influenced by the plasma plume, which showed markedly different responses to the laser-coatings interaction. By comparing the form of damage crater and layer peeling -off through SEM analysis and step profiler, it was found that more laser energy dissipated into the target with the decrease in ambient air pressure. For the reverse damage process in air and vacuum, materials ejection by the continuous impact of the laser energy was observed and the forms of materials ejection and damaged craters were the same. Investigating the materials response under different air pressure conditions provided valuable insights into the damage mechanisms during the nanosecond laser-induced damage of optical coatings.

Ta2O5/SiO2 mixed film is a very promising material for the preparation of new optical and optoelectronic devices, but there are few reports on its etching characteristics. In this paper, Ta2O5/SiO2 mixed films with various proportions of Ta2O5 were prepared by ion-beam sputtering deposition. CHF3-based reactive ion etching (RIE) was used to etch Ta2O5/SiO2 mixed films. The etching profiles of Ta2O5/SiO2 mixed films were observed by using a field-emission scanning electron microscope (SEM). The RIE etch rates were investigated as a function of the Ta2O5/SiO2 mixture ratio, RIE power, chamber pressure and etching gas ratio. It is found that the etch rate of Ta2O5/SiO2 mixed films increase with an increase of RIE power and chamber pressure, and decrease with an increase of Ta2O5 composition in the Ta2O5/SiO2 mixed films. Moreover, it is also found that as the proportion of F-based gas increases, the etching rate of the Ta2O5/SiO2 mixed film first increases and then saturates. These results would be of importance for the fabrication of optical and optoelectronic devices based on Ta2O5/SiO2 mixed films.

High-repetition rate laser-induced damage of Ta2O5:SiO2 coatings was investigated at 355 nm wavelength and a repetition rate of 30 kHz. Laser-induced damage thresholds of coatings with different mixture ratios were measured. The relationships between laser-induced damage threshold and the material band gap and defect absorption were analyzed. Laser-induced damage threshold decreased with increase in number of laser pulses owing to enhancement of the absorption. Enhancement of absorption is attributed to the increase in density of mid-state defects induced by the picosecond laser pulses. The relationship between mid-state defects and the material mixture ratio was also analyzed.

Vacuum-air-shift causes trouble to conventional electron beam evaporation (EBE) coatings. This study compares the protection effect of ion assistance and the ALD (atomic layer deposition) Al2O3 capping layer. The vacuum-air-shift was reproduced on an EBE Ta2O5 single-layer film, a Ta2O5/SiO2 double-layer coating, and a high-reflectance mirror. Similar samples were prepared by EBE assisted with ion beam bombardment. Part of the as-deposited coatings were capped by ALD Al2O3 film with a thickness of about 100 nm. The vacuum-air-shift of the samples was tested with an in-situ spectrophotometer. The cross-section of the coatings was imaged by a scanning electron microscope. The ion assistance was found to reduce the vacuum-air-shift to a limit extent, while the ALD capping film was found to eliminate the vacuum-air-shift. The mechanism of the two protection techniques was analyzed, and their usage was compared and discussed. The ALD capping technique may be used in high precision EBE coatings with convenience and low cost.

Functionally graded layers (FGLs) with quasi-continuous interfaces are deposited by ion-beam sputtering (IBS). The laser-induced damage threshold (LIDT) of FGLs is more than twice that of film-substrate interface. Basic time-resolved microscope system is designed to capture the ultrafast dynamics process of nanosecond laserinduced damage in FGLs and film-substrate interface, respectively. Materials ejections and damages craters at the film-substrate interface are observed by focused ion beam (FIB) microscope. The primary sources leading to low LIDTs are the nano-precursors distributed among the subsurface. The nano-precursors formed by the metastable chemical structures (FeOx and CeSixOy) are agglomerated and grown during migration process because of sputtered atomic collision motion. High normalized electric field intensity enhancement in the subsurface region (about 275 nm) is considered to be an important factor that promotes absorption of the nanoprecursors. The experiment first provides a sufficient experimental observation of the laser-induced damage process inside films which deepens people's understanding of nano-precusors and lays a solid basis for solving the damage of film-substrate interface.

Laser damage threshold of optical components is an important indicator to measure the ability of components to resist laser damage. A low-absorption film is plated on the surface of the reaction sintered SiC substrate produced by ion beam sputtering method, and the fundamental frequency reflection efficiency is over 99.8%. A set of 1060 nm continuous laser damage threshold testing system has been established. After loading the SiC-based film sample with a continuous wave laser with a power density of 30 kW/cm2 for 30 s, it was found that the surface temperature rise of the SiC-based film was less than 2 K. the changes of temperature field and thermal stress on the surface of the SiC mirror when the continuous laser loading power and loading time by finite element method. The results are basically consistent with the experimental data. The experimental results verify that the thermal stress and thermal melting effect caused by high-power continuous laser loading are the mechanisms for the damage of mirrors, which provides an idea for improving the laser damage threshold of optical components.

Nanosecond pulse laser-induced damage is associated with nodular defects and nano-precursors in hafnium oxide (HfO2)/silica (SiO2) multilayer films. In this study, the dynamic evolution of material ejection and layer peelingoff in HfO2/SiO2 thin-film beam splitters used for third harmonic separation were examined by time-resolved shadowgraph technique under the fundamental frequency of 1064 nm (1 omega) and third harmonics 355 nm (3 omega) laser beam, respectively. The initial material ejection and subsequent peeling-off of layers were studied to clarify most thin films damage events caused by 1 omega and 3 omega lasers. The peeling-off of films under 1 omega laser was mainly caused by thermomechanical effect. In contrast, the peeling-off of films under 3 omega laser was mainly affected by laser-induced mechanical damage. The different transmission forms of layers peeled off from the films revealed the influence of mechanical strength and thermal strength on damage progression. The Taylor-Sedov theoretical model was used to analyze the propagation characteristic shock waves after nanosecond laser irradiation of films. In summary, identification of propagation forms and speed of peeling-off layers provides helpful insights into the damage mechanisms during nanosecond laser-induced damage of optical thin films.

A near-surface redeposition layer is formed in the chemical mechanical polishing process of silicate glasses. In this work, secondary ion mass spectroscopy analyzer and transmission electron microscope are used to investigate the effect of bulk and pad materials on the microstructure and contaminations of the redeposition layer. The results suggest that the polishing materials with higher chemical reactivity will generate a deeper redeposition layer with higher concentration of contaminant elements, which will improve the surface quality by mitigating the mechanical abrasion effect. Then, a more detailed chemical mechanism of the redeposition layer formation has been concluded according to the chemical reaction and arrhenius equation, which can explain the effect of bulk materials and polishing pad on the redeposition layer well. These findings are helpful to understand the chemical process of polishing and improve the lifetime and quality of optical components especially in UV or high-power laser systems.

Several series of HfO2/SiO2 mixture coatings with different mixture ratios were prepared via ion beam sputtering. The physical properties of the coatings were measured, and the damage characteristics induced by nano-precursors in each of HfO2/SiO2 mixture coatings were investigated. The number of microscale pits induced by nano-precursors decreased while passing from pure SiO2 towards the HfO2/SiO2 system, and melted regions became significant at HfO2 concentrations above 50%. Some damage microscale pits induced by nano-precursors exhibited cracks perpendicular to the laser polarization, and laser-induced periodic surface structures were formed under higher fluences and about 75% of HfO2. The damage morphology patterns revealed that the damage mechanisms were dominated by the nano-precursors in the subsurface layers and various thermal adsorption characteristics of the mixture coatings.

Restricting polishing induced subsurface damage and obtaining super smooth surfaces are important in high quality laser systems. Here, experiments and theoretical simulations are combined to investigate correlations among particle size distribution, subsurface damage distribution, and surface roughness evolution in the optical polishing process. This reveals that the fraction of observable subsurface damage increases rapidly with increased particle size, which results in greater and deeper subsurface damage. In addition, control of the tail end particle size distribution is also critical for controlling polishing-induced subsurface damage. In the high surface roughness period, the surface roughness increases linearly with increased subsurface damage. In the low surface roughness period, without any polishing induced subsurface damage, optimizing pad properties to reduce microscale surface undulation could further improve surface roughness. Making sure that no observable subsurface damage is generated is the precondition for obtaining a super smooth surface. Using nanosized particles could greatly reduce the particles' bear load and finally obtain a super smooth surface without any subsurface damages.

Atomic layer deposition has promising application in optical coatings because of the self-terminating feature. An ideally self-terminating ALD process is based on the saturate chemi-sorption and complete purging of the desorbed precursor molecules. The kinetics of adsorption and desorption are analyzed, providing instruction for the development of ALD process. The exposure length is related to the partial pressure and molecule mass, while the purging length is dependent on the physi-sorption potential energy and substrate temperature. The GPC versus pulse length of ALD Al2O3 and HfO2 are measured. With a set of properly selected parameters, film layers with distinctive self-terminating feature are obtained. A coating consisting of several nanolaminates is analyzed with TEM to study the ALD film structure. An anti-reflection coating is deposited, controlling the film thickness by counting the cycles. The laser resistance of the ALD Al2O3 film, HfO2 film and anti-reflection coating is studied. The results certify the analysis and indicate a promising application in developing a self-terminating ALD process for a new material on a new plant.

Ion beam etching through physical sputtering can also improve the laser-induced damage threshold of fused silica optics without introducing precipitation products or toxic fluoride solution, which makes ion beam etching an attractive alternative method for post-treatment. Researches indicated that ion beam etching could partially remove surface scratches and reduce the surface roughness of fused silica optics. In this study, the effects of ion beam etching on surface/subsurface structural defect evolution of fused silica optics were investigated. The results showed that chemically inert ion beam etching completely removes plastic subsurface structural defects and partially removes surface structural defects. Because of the lack of a sacrificial layer, ion beam etching has much lower removal efficiency for surface structural defects, especially deep structural defects, than for subsurface structural defects.

This paper investigated the laser-induced damage mechanism of amorphous and crystalline scandium oxide (Sc2O3) films prepared by ion beam sputtering (IBS) and annealed at different temperatures. A significant increased laser-induced damage threshold (LIDT) at 355 nm wavelength was obtained by amorphous film annealed slightly below the crystallization temperature, which was above 300% higher than those of crystalline films. Meanwhile, the damage morphologies of amorphous and crystalline films were totally different. Measurement of the absorption of films showed that higher absorption led to a large distinction between the LIDTs of films. Energy dispersive spectroscopy (EDS) patterns revealed very uniform distributions of elements without obvious aggregation phenomenon. Positron annihilation spectroscopy (PAS) indicated that vacancy defect increased the absorption and heavily reduced the resistance of films for 355 nm wavelength laser. The investigation in this study would promote the understanding of the laser-induced damage mechanism of amorphous and crystalline films and provide an effective method to increase LIDTs at 355 nm wavelength.

We present a method of using computer-generated hologram (CGH) to measure the radius of curvature of large aperture long-focal-length lens. In this method, a large aperture transmission CGH is used as a transmission sphere to generate the test and reference wavefronts by means of diffraction. To verify the feasiblity of this method, a 450 mm × 450 mm transmission CGH is designed and fabricated for measuring the radius of 440 mm × 440 mm spatial filter lens. Experimental results and error analysis show that the CGH test method features high accuracy and good repeatability.

Automatic measurement of single points schema by coordinate measuring machine(CMM) is used to measure the Ultra-Long curvature radius of spherical optical element. The removal quantity of each measuring point can be calculated through contrasting the measure value and the theoretical value. A removal model of spherical optical element polishing is established based on Preston equation, and the required machining parameters are predicted by removal simulation in MATLAB. A processing test on a fused silicon with an aperture of 440mm x440mm was perfouned and the result shows that the model is effective in Ultra-Long curvature radius control of spherical optical element during full aperture polishing.

结合自身实验条件采用电子束蒸发(EBE)、离子束溅射(IBS)和原子层沉积(ALD)三种工艺制备了HfO2薄膜,对其进行退火实验,采用1064 nm Nd:YAG激光测定了即时沉积和退火后各HfO2薄膜的抗激光损伤能力.研究发现,ALD HfO2薄膜的激光损伤阈值最高,EBE HfO2薄膜次之,IBS HfO2薄膜的损伤阈值最低;300℃退火对各工艺薄膜抗激光损伤能力的影响均为负面,500℃退火则会显著降低ALD HfO2薄膜的抗激光损伤能力.

Aiming at the improvement of edge effect in CNC polishing. A new polishing method based on the surface extension is proposed. The basic idea and workflow are presented. The availability of this method is verified by simulation. Experimental study was carried out on 420mm×420mm caliber fused quartz optical element. The experimental results show that this method can restrain the collapse and warped edge surface. PV less than λ/3，GRMS less than 7.7nm/cm and PSD1 less than 1.8nm can be obtained combining the small scale smoothing technology.

This article mainly take the research in controlling the parallelism of the Phi 200mm x 10mm sapphire window during the polishing fabrication. First, in the period of full aperture polishing ,by adjusting the polishing parameters ,the parallelism of the sapphire window conversed to the level of below 3",then we took the sub-aperture ion-beam polishing technique to make the further convergence of the parallelism, in this precise polishing stage,with the ion-beam figuring machine IBF600, the parallelism error was converted to the surface tilt error map ,through the proper choice of the removal function and dwell time calculation, the thin sapph ire window's parallelism converged to subsecond accuracy which satisfied the application requirement of this element.

For large-scale high-power laser devices, the transmitted wavefront gradient root mean square (GRMS) is one of the most important indexes for evaluating the low-frequency distortion of spherical lenses. In this paper, for the low-frequency error index requirement of large-diameter spatial filter lens, a conformed polishing method based on composite tool is proposed in the spherical CCOS polishing stage. Based on the detection results of the optical components, the GRMS distribution is separated by low-pass filtering, and the high value of GRMS is partitioned by K-means algorithm to determine the polishing path and dwelling time. A composite conformed polishing tool is designed and the simulation analysis of the polishing tool structure and polishing stress distribution are carried out to optimize the parameters, in order to obtain an ideal GRMS convergence removal function. After experiments and production verifications of several 440x440 sized spatial filter lenses, the results show that the GRMS can be quickly converged below 7nm/cm, and the convergence rate is improved by about 50% compared with the traditional CNC polishing.

This article mainly take the research in controlling the parameters in the full aperture fine grinding and polishing stage of the 350mm×300mm×10mm size sapphire window. In the period of full aperture fine grinding period ,by adjusting the grinding parameters, the whole aperter parallel error of the sapphire window conversed to the level of below 3".In the period of full aperture polishing period , by adjusting the polishing parameters including the vaccum adsorbing parameterm, with those measures the wavefront error conversed to the PV value of 2λ(λ=632.8nm), the whole aperture parallel error of the sapphire window conversed to the level of below 3", and the inside arbitrary Φ100mm aperture’s parallel error also conversed to the level of below 3", the roughness of the polishing face attained to the value Rq≤2nm.Through the technical research in the full aperter processing of the sapphire window , the wavefront error, the parallel error and the surface roughness are well controlled which provide the fine results import in the fine sub-aperture polishing period.