This PDF file contains the front matter associated with SPIE Proceedings Volume 11063, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Quasi-CW laser damage process of indium tin oxide (ITO) thin film was investigated. The ITO film with thickness of 300 nm was deposited on fused silica substrate by magnetron sputtering. Experiments were conducted on quasi-CW laser with wavelength of 1064 nm, and the test was executed in single shot test with radiation time of 60 s. The damage morphologies were observed via optical microscope and scanning electron microscope (SEM). The apparent damage started with change in color which the morphologies were visible to the naked eyes. With the power density higher than the laser induced damage threshold (LIDT), there were cracks in the center of the damage site. The temperature distribution of the ITO thin film was investigated based on the heat equation.

This work is dedicated to the study of fatigue effects upon femtosecond laser-induced damage of Ta₂O₅/HfO₂/SiO₂ highreflective coatings irradiated by pulse train at 1Hz (65 fs, 800 nm). Upon on comparative measurements of different pulse numbers involving between 10 and 300 pulses, laser-induced damage threshold (LIDT) decreases and the multipulse LIDT decreased to the level of 70~75% of the single pulse LIDT. In addition, we found that the probability of damage performs an increasing trend with the number of pulse increases when the coating is irradiated with the same fluence. The evolution of LIDT and 100% damage probability threshold under multipulse irradiations revealed that fatigue effects were affected by both laser fluence and shot numbers. The deep defects play an important role in the multi-shot mode. A correlative theory model based on critical conduction band electron density is constructed to elucidate the experimental phenomena.

In order to analyze the mechanism of damage threshold enhancement after laser conditioning, the stimulated Raman scattering and fluorescent properties of un-conditioned and laser conditioned of DKDP crystals were compared in detail. It revealed that the intensity of Raman scattering peak 921cm^-1 were slightly lowered, and the intensity of fluorescence was much decreased, especially the fluorescence below 400nm, after nanosecond laser conditioning. Moreover, the intensity of fluorescence could be further decreased after sub-nanosecond laser conditioning. The slightly variation of Raman scattering proved the modification of the PO₄ vibrational modes. The sharply decrease of fluorescence intensity below 400 nm reflected the density reduction of electron defects in these crystals. On the basis of the above analysis, laser conditioning mechanism in DKDP crystals was discussed.

Laboratory air is one most popular transparent medium for high power laser beam propagation. Its threshold of laser induced breakdown is one of the key characters for the high power laser system. The thresholds of laser induced air breakdown under laboratory condition were measured using 1064, 532, 355, 266 and 248nm short pulse laser. The focal spot varies from 50μ m to 150μ m which achieved using a lens with 117mm focal length. The measured breakdown thresholds range from 3.2×10¹⁰W/cm² to 5.1×10¹¹W/cm², depending on the wavelength. It is confirmed that the KrF laser induced air breakdown threshold should be 3.2×10¹⁰W/cm², which is almost 1 order of magnitude higher than the reported value of 2.7 ×10⁹W/cm² .The measurements indicate multi-photon ionization is the dominant mechanism since the air breakdown thresholds at 1064, 532, 355, 266 and 248nm seemed well-agreed with the scale law of λ².

As a kind of typical material for mechanical structure, stainless steel is often adopted in the high-power laser facility. Iron elements in stainless steel may play an important role in resisting the effect of laser ablation. Laser ablation of stainless steel or aluminium alloy can also cause metal particle contamination in high-power laser facility. The ablation processes on iron surface under laser irradiation are investigated with molecular dynamics (MD) simulation combined with two-temperature model. The trajectories of atoms in each region of single crystal iron under laser irradiation are analyzed in terms of the interaction between laser and iron. The simulation results show that atoms absorbing different energy show the macroscopic characteristics of different phases of single crystal iron. Studies have also shown that single atom and clusters of atoms may have a backlash effect on the material and cause stress waves. The propagation of stress waves is also analyzed. It is shown that the velocity of the stress wave is about 6.094 km/s. Ablation threshold of single crystal iron is determined by the movement of surface atoms under different laser energy densities and the simulation results show that ablation threshold of single crystal iron under femtosecond laser is 0.18 J/cm². Meanwhile, it is also found that the instantaneous loading of laser energy has a greater effect on material ablation. This study can underpin for investigating the damage and contamination of precision mechanical component with stainless steel under the effects of laser irradiation.

The exceptional power scalability of Yb lasers has enabled the development of pulsed optical parametric amplifiers (OPA’s) operating at the short-wave edge of the mid-IR (MIR) with average powers beyond 10 W simultaneously providing peak powers in excess of 1 GW. Further wavelength extension into the longer-wave MIR is enabled by novel wide-bandgap non-oxide nonlinear crystals that can be pumped directly at 1 μm without detrimental one- and twophoton absorption of pump radiation. Eliminating the usual difference frequency generation step in producing MIR pulses above 5 μm could potentially increase the conversion efficiency of parametric down-conversion devices and enable a significant boost in the attainable average and peak power. Despite their utmost importance, material properties related to ultrafast laser-induced damage in nonlinear crystals are rarely investigated in the corresponding laser parameter range. In order to help unravel the complicated interplay of photorefractive effects, thermal lensing, and selffocusing/ defocusing affecting the beam quality and catastrophic breakdown threshold in MIR OPA’s, we present the nonlinear index of refraction at 1 μm of KTiOAsO₄, LiGaS₂, and BaGa₄S₇. The reported data provide crucial design parameters for the development of high-average-power MIR OPA’s. As examples, (i) a 100-kHz, 1.55/3.1 μm dual-beam OPA delivering multi-GW peak power in each beam and a total average power of 55 W and (ii) a 100-kHz, sub-100-fs, 1-μm-pumped OPA tunable in the 5.7-10.5-μm range are briefly presented.

By eliminating one prismatic face and adding four second pyramid faces, the horizontally oriented DKDP crystal can improve the cutting efficiency for tripler in ICF. To optimize the flow conditions for the growth of the horizontally oriented DKDP crystal, a stirring paddle is add above the crystal in the growth tank. With different rotation direction, position and size of the stirring paddle, the distributions of shear force on the crystal surface are compared by using numerical simulations. But the shear stress at center of the up face of the crystal is too small to ensure high quality crystal. However, the numerical simulation results do provide the understanding and guidance for the growth of large size DKDP crystals that can increase cutting efficiency of tripler. Currently, a cuboid DKDP crystal without a pyramidal sector was rapidly grown in SIOM. The higher the cuboid DKDP crystal, the cutting yield is more efficient for the tripler. And the aperture of the biggest triplers is approximately equal to the cross-section of the cuboid DKDP crystal. The fluence corresponding to 50% laser-induced damage (LID) probability of the cuboid DKDP crystal was 13.4 J/cm². The crystal grown using this method establishes the possibility of growing large cuboid DKDP crystals. Currently, rapid growth of cuboid DKDP crystals of more than 40 cm is underway.

Laser damage resistance is a key factor for the operation and the improvement of high power laser systems. Up today laser damage performance of optical components is mainly a defect related material characteristic. Metrology procedures have been developed to realize repeatable and accurate measurements of surface damage density due to nanosecond pulses. These measurement techniques were used to guide the improvement of surface damage resistance. Fractures must be eliminated from surfaces, in order not to suffer a damage growth phenomenon, whose exponential character will reduce the optical lifetime. High intensity hot spots due to beam modulations, spatial and/or temporal modulations, can also cause surface damage. Specific set-ups and experiments were carried out that allowed us to analyze and explain these phenomena: damage initiation mechanisms, damage growth and beam propagation inside the optical components. The presentation aims to highlight relevant progress on these topics (1) initiation mechanisms due to defects show two phases: a first incubation phase followed by the expansion one of the damage site ; it appears also that damage diameters are well correlated with the expansion fluence, (2) a refined bulk observation coupled to a fractal analysis allow the quantification of bulk damage and therefore to explain the laser damage growth and its dependence on beam parameters like pulse length and fluence (3) non-linear amplification of phase and amplitude modulations lead to the amplification of the spatial pre-existing small scale modulations that increase the laser energy density locally and finally the number of damage sites. The whole of results, damage initiation, damage growth and beam propagation, is discussed to the light of the laser damage observed on LMJ optics.

Laser induced damage in the final optics assembly (FOA) is one of the bottleneck problems in high power laser systems for the inertial confinement fusion. In the online experiment, a correlation between the transport mirror defects and the optics damage in the final optics assembly has been found. A physical model is built to analyze the influence of defect size and modulation depth on the light intensification in the FOA. Basically, small size defect on the mirror has a tiny influence on the downstream modulation in the FOA. Optical propagation simulation is also carried out with the real defect phase information got from the interferometer. Results show that there could be strong light intensification caused by the upstream mirror defect. So the local high enough intensity is the main reason for the optics damage. The abnormal intensification is mainly caused by the irregular defect contour, which is produced in the laser induced damage process on the mirror. It is best to eliminate this kind of coating defect on the transport mirrors. When this kind of damaged defect on the transport mirror is inevitable, a mitigation strategy for the optics damage in the FOA is proposed. An inverse design of the best distance between the transport mirror and the FOA can be used to reduce the influence of the transport mirror defects on the downstream FOA. The study can provide some reference for the improvement of the damage resistance of final optics assembly in the high power laser facility.

Efficient removal of SiO₂ contaminated particles from sol-gel SiO₂ filmed fused silica surface was achieved by single shot dry laser cleaning and airflow displacement system assisted laser cleaning using a Q switched Nd:YAG pulse laser at 355 nm in wavelength. The experiment result shows that for single-shot laser dry cleaning of sol-gel film fused silica samples under the condition of satisfying the theoretical cleaning threshold, the optimal laser energy density was 2.28 J/cm², which is different from the process parameters of uncoated fused silica. In the optimal process parameters, single shot laser cleaning had obvious cleaning effect on SiO₂ particles with particle diameter larger than 1 μm, and the removal ratio was 64.81%. When the density of particle was too high, the cleaning effect was weakened and the damage to the substrate was caused. The re-attachment of crushed particles also leaded to making the cleaning effect worse. The airflow displacement system assisted laser cleaning method further enhanced the effect of removing the optical surface contaminated particles and the decontamination efficiency was improved to 80.53% at 1.71 J/cm². Our results demonstrated that airflow displacement system will be useful for single shot dry laser cleaning of SiO₂ particles on an optical surface of fused silica.

Fused silica is used as windows or lens in high power laser system. Slight laser absorption in it may results in huge damage caused by thermal effects. In order to reduce the bulk optical absorption in fused silica, mechanism of laser absorption in fused silica was studied from the perspective of structural defects. Ultra-purity fused silica was synthesized by high frequency plasma chemical vapor deposition (PCVD) process. Characteristics of structural defects includes hydroxyl, metal impurities, oxygen vacancy, bubbles and invisible stripe were studied by transmission spectrum, infrared reflection spectrum, stress birefringence, confocal microscope and impurity analyses. Formation mechanism of structural defects in fused silica was analyzed according to deposition process and vitrifying mechanism of silica. And influence of structural defects on bulk optical absorption was analyzed. By controlling structural defects, ultra-low laser absorption fused silica was synthesized by PCVD process.

Multiple-pulse laser-induced damage is an important topic for many applications of optical coatings. In this work, we study the performance of multiple and single pulse laser-induced damage of anti-reflection (AR) coatings with ns-pulsed laser irradiation at a wavelength of 355 nm. LIDT of AR coatings changes little under multiple and single pulse irradiation, around 15 J/cm². The damage probability curve of multiple pulse is extremely steep. The defect density in the irradiated area is quite high, a large amount of pin-point or cone-shaped pits are observed. The absorption coefficient and defect density increase a lot under multiple pulse irradiation. Material modification of the precursor under multiple pulse is thought as the main reason of high absorption coefficient. Once damage occurs, the damage increases fast and soon grows catastrophic damage. The initial damage morphologies are similar, pin-point or cone-shaped pits, which indicates the initial precursor or defect of multiple and single pulse are the same.

Many optical properties can be obtained from those propagation modes of optical micro/nano fiber, such as single-mode or hybrid-mode operation, power density distribution, strong confinement, large evanescent field and transmission loss. Here, the TE and TM polarization fundamental modes of straight and circularly bent optical micro/nano fibers are simulated respectively using the beam propagation method in 3D model of the commercial Rsoft software. The curves of launch power versus propagation distance at different bending radii and optical wavelengths are then obtained, which indicates the 90° loss and even the longer propagation distance loss are so small that can be ignored when the bending radius is large enough to some extent. And also the transmission loss reduced with the decrease of optical wavelength is revealed. These modeling results might give a valuable insight for understanding the evaluation and application of optical micro/nano fiber, especially in the integrated optical fiber sensing area..

Low dispersive with broad bandwidth mirrors serve as indispensable elements in ultrafast laser systems. We report on three coatings, quarter-wave high reflection mirror, metal-dielectric mirror and ternary composite mirror, which are suitable for broad bandwidth high reflection (BBHR) with 800nm center wavelength. Mirrors based on quarterwave Ta₂O₅/SiO₂ layers are designed and fabricated. By depositing the quarter-wave HfO₂/SiO₂ layers on the metallic material, we have achieved the mirror with lager low-dispersive bandwidth, this design takes advantage of broad high reflection bandwidth of metal and high laser induced damage threshold (LIDT) of HfO₂. Moreover, we have deposited HfO₂/SiO₂ layers on Ta₂O₅/SiO₂ layers, since HfO₂ demonstrates higher damage threshold than Ta₂O₅, such combination reach an ideal trade-off between the low-dispersive bandwidth and high LIDT comparing with traditional quarter-wave Ta₂O₅/SiO₂ layers. Our BBHR mirrors are produced by means of dual-ion-beam sputtering technique. The designs afford low group delay dispersion (GDD) for reflected light over the broad bandwidth in order to minimize temporal broadening of the fs pulses. The design’s GDD behaves in a smooth way, and its electric field intensities show promise for high LIDTs. Reflectivity and GDD measurements indicate good performance of the BBHR design. LIDTs of the produced BBHR mirrors are also tested and compared.

Linear rolling guide have widely used in precision machinery today, with significant advantages such as high precision, low traction and low wear. Research on the dynamic characteristics of precision linear rolling guide became very important for space applications due to the continuous improvement of the manufacturing level of high-precision equipment. The THK's RSR small precision guide is studied in this research. The model of guide joint is established by optimized tandem damping element with the finite element method to simulate the dynamic stiffness and ball mass of the guide joint. The analytical formula based on Hertzian contact theory is adopted in this research to obtain the dynamic parameters of the guide joint. Accomplishing the the dynamic simulation analysis of the precision guide based on the finite element method by MSC.Patran & Nastran software.

In this paper, a new type of focusing mechanism for space telescope is designed to compensate defocusing caused by alteration of space condition in orbit. The focusing mechanism is driven by a stepping motor and a worm gear reducer, transmitted by a ball screw and output by a flexible hinge. It has advantages of low mass, small overall size and especially high accuracy that is better than 1 micrometer. As one of main parts of focusing mechanism, the flexible hinge is mounted in the focusing shaft and connected to the nuts of ball screw kinematic pair which has mechanical end stops. The focusing shaft is guided by two couples of thin film boards to ensure the precise displacement along optical axis direction. The secondary mirror frame is connected to the shaft to complete focusing. Firstly, the focusing mechanism is designed, and the design scheme is illustrated in this paper. Then a modal analysis with finite element method for the mechanism is completed. The results show that the dynamic stiffness is high enough and meets the requirement.

It has very important application value to investigate the damage mechanism of CaF₂ windows irradiated by ultraviolet excimer laser. As significant optical materials, CaF₂ windows have been widely used in the ultraviolet photoelectrical field. Because the ultraviolet excimer laser presents favorable characteristics such as short wavelength and high photon energy, the high power excimer lasers are expected to be widely applied in precision laser machining and military field. In this paper, the experiment on damage in CaF₂ windows irradiated by 248nm ultraviolet excimer laser was carried out. The damage characteristics of irradiated spots under different experiment conditions were detected by optical microscope. The laser induced damage thresholds of CaF₂ windows were calculated by the zero damage probability through linear fitting. The damage mechanism of CaF₂ windows were discussed based on the surface characteristics of damage spots. The experimental results indicated that the damage thresholds of zero probability for the 248nm excimer laser to CaF₂ windows were 5.6J/cm² of the incident surface, and 1.1J/cm² of the exit surface respectively. When CaF₂ windows was irradiated by 248nm excimer laser, its damage first occurred to its exit surface, the damage threshold of exit surface was smaller than that of incident surface. As the laser fluence increased gradually, the damage of exit surface was shown to grow exponential and its degree was significantly higher than that of incident surface. This work is helpful to further improve damage resistance of CaF₂ windows in high power laser facility. It can provide the necessary references for selection of ultraviolet optical materials and optimization of application.

In order to improve the laser-induced damage threshold (LIDT) of thin film optical elements in laser systems, the thermal damage and thermal stress damage processes in thin films induced by laser are analyzed. Based on the theoretical knowledge of heat conduction, material mechanics and thermoelasticity, the mathematical model of multilayer optical thin films irradiated by single-pulse Gauss laser is established. The active heat conduction equations and thermoelastic equilibrium differential equations under the model are established. The analytical solutions of temperature and thermal stress in multilayer optical thin films induced by laser are derived and calculated. Through software calculation and simulation, the distributions of temperature field and thermal stress field are obtained. By discussing and analyzing the simulation results, the influencing factors and distribution rules of temperature rise and thermal stress are obtained, which provide theoretical basis for preparing thin films with high laser-induced damage threshold.

The issues of laser-induced damage of transparent dielectric optics severely limit the development of large laser systems. In order to explore the mechanism of nanosecond laser damage on KDP surface, a multi-physics coupling dynamics model and a time resolved detection system were developed to obtain the transient dynamic behaviors of laser damage. The behaviors of laser energy transmission, thermal field distribution and damage morphology during nanosecond laser irradiation on KDP surface were simulated. It is found that the enhancement of light intensity caused by surface defect plays an important role in the initial energy deposition and damage initiation of the laser irradiation area. The evolution of the temperature field and fluid flow during subsequent laser irradiation contributes to the laser damage process. The simulated evolution of heat absorption source is verified by the transient images of local defect-induced laser damage captured by the ultra-fast experimental detection system. This work provides further insights in explaining the laserinduced damage by surface defects on KDP crystals.

A lidar based on UV laser is developed to observe air quality in Beijing. The initial laser wavelength is 1064 nm, and an emission wavelength of 355 nm is obtained after the second-harmonic generation and third-harmonic generation. The output energy is 30 mJ/pulse, and the pulse width is 7 ns. Echo signals are collected by a 304.8 mm diameter Newtonian telescope. With high-power ultraviolet laser excitation, the intensity of atmospheric pollutants is studied by the laserinduced fluorescence (LIF). The Mie scattering is detected simultaneously and both signals are detected by the photomultiplier tubes (PMT). The system is calibrated by a series of experiments. The aerosol extinction coefficient retrieved by Mie signal from this system agrees well with that from another lidar with a laser wavelength of 532 nm. The fluorescence efficiency of atmospheric pollutants are obtained by calculating the fluorescence-to-Mie ratio (FMR). The time and spatial resolution of the system are 5 s and 7.5 m, respectively. The continuous change of air quality over a period of time is studied by the mean value of FMR. Many observations are carried out under different air quality conditions, and the experimental results are in good agreement with the results of the ground observation station. In summary, this method based on UV laser is feasible in the field of atmospheric remote sensing and have potential applications in the field of air quality monitoring.

In the current research of solving the energy problem, the Inertial Confinement Fusion (ICF) has been studied for many years, which drives the occurrence of nuclear reaction in a multi-beam laser focusing system. And in this system, multiple laser beams in different directions are focused at the same surface to produce sufficient light energy. Generally, if the stray light reflected by the focusing surface returns back toward one of the laser systems and then is focused into ghosts with high energy, the optical components near the ghosts will be influenced or damaged. For each laser in the multi-beam laser focusing system, the influence of internal stray light and the effect of stray light generated by other laser need to be considered. Based on the study of the National Ignition Facility (NIF), analysis of stray light reflected from multi-beam laser focusing surface was proposed in this paper. Modeling and simulation based on the law of light propagation and Monte Carlo analysis were demonstrated. Ray tracing and the analysis of stray light were carried out in the focusing system. The distribution of stray light on the observation sphere and the optimization rules of array structure were obtained. Finally, we got the optimal structure with d = 2 mm and R = 3 mm, which can better meet the requirements of uniformity and back-to-hole energy.

In this paper, the laser-induced fluorescence (LIF) technology is utilized for rapid assessment of the purity of quartz glass, especially for the screening of high-purity quartz glass. A 355 nm laser was applied as excitation source to induce the fluorescence signal of the quartz glass samples. The fluorescence signal is then transmitted to the spectrometer through an optical fiber for spectral acquisition. Because only the impurities in quartz glass induce fluorescence, purity quartz glasses does not have a distinct fluorescence signals or fluorescence peaks. The purity evaluation of high-purity quartz glass can be achieved by analyzing the obtained signals. The standard deviation and the ratio of the maximum to minimum values of the signals were calculated to indicate the intensity of the fluorescent peak of the signal. The thresholds were then set to distinguish between high-purity and low-purity quartz glasses. The method has the advantages of high speed, high precision and high reliability, and is of great significance for the rapid screening of quartz glass with high purity requirements.

We have designed and demonstrated an all-fiber laser which can switch the operation mode between the pulsed mode and the continuous mode. Under the pulsed operation mode, the maximum output pulse energy is measured to be 120 μJ with a pulse width of 400 ns. The pulse width is continuously adjustable between 100 ns and 600 ns. Under continuous operation mode, the maximum output power is 2 W. Switching between these two operation modes can be done with simple instructions within several milliseconds. Large-mode-area (LMA) fiber amplifiers are adopted to support the high peak power. The LMA fiber amplifiers are coiled in a circle with a diameter of 25 cm and the high order transverse mode are suppressed by the bending loss. The M squared factors of the designed laser are 1.204 on x-axis and 1.293 on y-axis. This laser is optimized for coherent Doppler lidar system that can detect at both the near (within several tens of meters) and far distance (more than a dozen kilometers).

Laser-induced damage is still the key issue to restrict the development of high power laser system for inertial confinement fusion (ICF). Based on a high power laser prototype, laser-induced damage behaviors and performance of large aperture final optics were experimentally studied. And, the damage inducement and morphology were comprehensively analyzed. Probability density functions (PDF) for laser fluence of near field with different resolution were obtained to analyze the influence of optical field distribution on the optical damage. High fluence of the near field was revealed in PDF with higher resolution, and the missing strong modulation fractions in the measured near field was most probably damage the optical elements. The surface damage morphology was observed and the main damage mechanism was discussed. Several kinds of surface damage morphologies with individual characteristics were sorted. The ratio of width and depth and the main contributors of laser damage were discussed.

In high power laser system, the 3ω laser fluence can up to 6J/cm² with triple frequency conversion efficiency up to 75%. Two high fluence laser experiments have been done for proving high efficiency output and damage resistance of KDP crystal. The KDP crystals have different performance in these two experiments due to their characteristics nuances. For the third harmonic crystal in first experiments, centimeter damage occurred on this crystal after about 50 number laser shots, and more than ten thousands micrometer damage points occurred on this crystal. For the second KDP crystal after about 60 number laser shots, most damage size are micrometer, including bulk damage and damage on back surface, micrometer damage doesn’t exist because of its good quality. We classify these damages of crystals to different kinds, observe characteristics of these damages. Observation of laser damage on third-harmonic converter crystals have been done in this paper.

In high-power laser systems, the optics suffers from different degrees of damage due to high-power laser irradiation. Studying the laser-induced damage generation and growth law of the optics is greatly benefited by the ability to accurately predict how damage sites evolve with laser exposure. In this work, the laser-induced damage growth model in optics under high-power laser irradiation is described based on the Weibull distribution model. A parameter method for solving Weibull distribution model by using the least-square method is proposed. In addition, a Monte-Carlo analysis method is used to numerically simulate the growth law of laser-induced damage in optics based on the statistical theory. Furthermore, we have also predict the laser-induced damage growth trend for 20 shots in high-power laser systems.

Guideway of the measuring system can affect the measuring accuracy. In order to provide a high-precision motion reference for the coordinate measuring system, this paper proposes the use of ultra -low expansion glass as the material of the measuring platform guideway, and optical processing is introduced to improve the surface accuracy. Meanwhile, guideway edge is easy to produce edge effect and the high-precision measurement is difficult, the combined processing method of magnetorheological finishing, CCOS large disc by circle motion and linear motion of rectangular plate is proposed, and the guideway is measured by sub-aperture stitching method. The results show that the Peak-Valley value of the 1000×240mm² glass guideway surface is 0.347μm and the Root-Mean-Square value is 0.033wave1wave=0.6328μm). Moreover, the edge effect is controlled in the process. Ultimately, the accuracy of the one meters long glass guideway is reached at deep sub-micron level, and the combined processing technology is verified to be feasible.

The fused silica glass is widely used in the photoelectricity and semiconductor industry, and needed to be cut or made small holes and micro grooves on it. Recent reports indicate that laser processing is one of important means for fused silica glass. First of all, the laser processing characteristics of fused silica glass was discussed in this paper. Besides, 532nm wavelength and CO₂ laser were used to process or cut fused silica glass, and different results were found. 532nm laser is more suitable for processing holes and micro grooves on thin fused silica glass. Then CO₂ laser can be used to cut thick fused silica plate or marked on the glass surface. In addition, the two laser machined surface was observed with 3D microscope, and it displays huge surface differences. The first one is rough, and another is smooth.

In this paper, the method of Radial basis function(RBF) to Electronic Speckle Pattern Interferometry (ESPI)information extraction is studied, mainly including: the filtering method based on radial basis function for ESPI fringe patterns with wide density; introducing the radial basis function to interpolate the number of fringe in the fringe skeleton method. Thermal deformation phase measurement of Al₂O₃ ceramic substrate at the circumstance of thermal load was estimated based on the ESPI. In the experiment, four ESPI fringe patterns at different moment at the beginning of the experiment were captured. The RBF filtering method and the fringe skeleton method with RBF interpolating were used to estimating the thermal deformation phase measurement. The acquiring out-of-plane displacements by our method were in good agreement with the real deformation under the stepped-up thermal load gradually. This measurement can provide assistance for studying the performance of ceramic substrate in the process of laser processing.

In this paper, we designed the broadband all-dielectric reflection phase shifting mirror to convert the linear polarization incident light to circularly polarization reflected light in the design wavelength range (750nm~850nm) for ultra-high intensity laser application. The 48 multilayer coated mirror used Ta2O5 and SiO2 as high and low refractive index materials. The theoretical design results indicated that at the incident angle 45 degree, the reflectivity of s- polarization light exceeded 99.9% and p- polarization light exceeded 99.5%, and phase shift values between s- and p- polarization lights were -90±5 degrees in the design wavelength range. The all-dielectric broadband reflection phase shifting mirror was fabricated with an ion beam sputtering system. The measurement results indicated that the reflectivity of s-polarization light exceeded 99.9% and p- polarization light exceeded 99.3%, and phase shift values between s- and p-polarization lights were -95~-77 degrees. The reflectivity of s- polarization light and p- polarization light conform well to theoretical design values. However, the phase shift values slightly deviated from theoretical design results in part of the wavelength range. With features of high reflectivity and invertible linear to circular polarization conversion, the all-dielectric broadband reflection phase shifting mirror can be a good replacement for quarter wave plate in high intensity laser region, and offers a further step in developing polarization and phase manipulation devices.

When Potassium Dihydrogen Phosphate (KDP) crystal is irradiated by nanosecond laser with fluences exceeding its damage threshold, laser-induced damage occurs in the bulk or on the surfaces of crystal components. Such damage process is a multi-physical coupling process which is composed of energy deposition stage, temperature/pressure rising stage and subsequent micro explosion stage. So far, great efforts have been made in modeling the energy deposition and temperature/pressure rising stages of the damage process, but little attention has been paid on the subsequent micro explosion event. As a result, it is still impossible to reproduce the laser damage phenomena such as damage crater formation and shockwave propagation with the existing damage models. To address this concern, equivalent explosion simulation model for studying the laser-induced damage process of KDP crystals has been constructed by finite element method (FEM). According to the model, explosion energy leading to damage, formation of damage craters and propagation of shockwave can be obtained. Moreover, laser damage experiments combined with time-resolved techniques have been utilized to investigate the impact of laser fluences on the shockwave speed. Experiment results agree well with the simulated phenomenon, which has proved the validity of the simulation model.

High-voltage and ultra-high-voltage power grids are important physical transmission grids for long-distance and largescale electric power transmission in electric systems. Transmission lines exposed to natural environment are often entangled by non-metallic foreign bodies, which are liable to cause major power supply accidents, so foreign bodies must be removed. Because the high-voltage line is far from the ground and the environment is complex, it is difficult to remove foreign bodies. Traditionally, electricians or robots remove foreign bodies from high-voltage lines after power failure, foreign bodies in high-voltage lines are removed by equipotential method in live operation. These methods require more manpower and physical resources, and the operation procedures are complex and time-consuming, the work intensity is high, and the safety is low. Laser has many advantages, such as good directionality, fast speed, high energy density, flexibility and accuracy, it has a good application prospect in the field of removing foreign bodies from transmission grids. In order to remove foreign bodies from high voltage transmission lines safely and quickly, the ablative mechanism of polymer plastics by CW laser is analyzed and an experimental device for laser ablation of polymer plastics is set up. In this article, experiments were carried out to study the ablation of polymer plastics wound on high voltage transmission lines by CW lasers with different power at different distances. The experimental results show that the laser power for ablating polymer plastics will increase greatly with the increase of distance. When the laser power is 50W, the maximum distance of ablating polymer plastics is 35m.With a similar situation, when the power is 100W, the maximum distance is 80m. And when the power is 150W, the maximum distance is 100m. The maximum distance is 150 m when the power is 300W.

Measurement of the low damage threshold defects in a large aperture fused silica glass is of great significance. Currently, the popular characterization method for detecting the low damage threshold defects is via measuring the optical absorption of a fused silica glass using the surface thermal lensing technology. However the detecting area of a single shot in this method is too small, typically around 10×10 microns, so if a large aperture fused silica glass in the size of 400×400 mm is to be measured, it would take approximate 100000 hours to complete the measurement, which is obviously not acceptable. Here, we report a fast measurement technique for obtaining the low damage threshold defects in a large aperture fused silica glass according to its fingerprint spectrum, for the fused silica optical glass in the size of 400×400 mm, measurement of the low damage threshold defects in the whole surface in several hours is achievable.

High repetition rate picosecond laser induced damage properties of Ta₂O₅/SiO₂ dielectric reflective optical coatings were investigated. The laser induced damage was attributed to the increase of the free electron density and temperature enhancement during the irradiation of high repetition rate picosecond laser. The correlation of laser induced damage threshold with pulse numbers was researched. At higher repetition rate, the laser induced damage threshold was reduced more with the increasing of pulsed number. We found that the defects absorption played an important role to the laser induced damage properties of dielectric reflective optical coatings. The damage morphology showed that the evolution of damage site was significantly influenced by the accumulation of laser energy. In order to enhance the resistance capacity, the dielectric reflective optical coatings were annealed with temperature of 260°C. The defect absorption was reduced after the annealing process. For the annealed coating, the laser induced damage threshold under high repetition rate picosecond laser was enhanced as a result of the suppression of defects in the coating.

Interest in the YAG (Y3Al5O12) transparent ceramics for laser systems has been increasing. As the laser gain medium in laser systems, especially in high power laser systems, the laser damage resistant of YAG ceramics are required to be evaluated. The laser damage characteristics of four ceramics with the dimensions of 30mm×15mm×3mm were investigated. It is found that the bulk laser induced damage thresholds (LIDTs) of the YAG ceramics are lower than their surface LIDTs. The bulk LIDTs are related with the transmissions of the YAG ceramics. The surface damage morphologies should be induced by the opens pores on the ceramic surface, which are left by surface manufacturing.

Laser induced damage on dielectric mirrors and its rapid growth with successive shots have been and continue to be an important barrier to high power laser systems. Here the morphology of mitigation pit is optimized theoretically, and an ultrashort laser is utilized to totally remove damage on both high-reflective (HR) and anti-reflective (AR) coating. At the same time, the substrate is handled carefully and free of laser ablation, which lower the scattering loss and the amount of debris during laser machining process. Then, using R-on-1 test procedure, several mitigated sites with size of 1mm× 1mm are investigated by a Nd:YAG laser system with a flat-top spatial distribution of fully covering the mitigated site. The experimental results show even at the average fluence of 18J/cm²@6ns, there’s no damage initiation on AR coatings and no damage growth on HR coatings. It demonstrates that ultrashort laser machining is an effective and robust way to mitigate laser damage and a promising way to improve dielectric mirror performance of high power laser system in volume production.

For avoiding the defect of introducing contamination for doped phosphate glass in conventional polishing technology, this paper proposes the machining method of Ion Beam Figuring(IBF). Material removal mechanism is also presented from a microscopic view. Surface roughness was analyzed by changing the incidence angle of normally and 20°. The results show that both surface roughness RMS are increased a little, and the PSD(power spectral density) of surface roughness RMS is shown, too.

It is an important factor for affecting camouflage effects, but copying background color with empirical color matching has poor accuracy. This paper chose cadmium red, cadmium yellow and other colors basing on the performance requirements of same-color same-spectrum; prepared pastes and swatches with different grinding times particle sizes, were to measure their spectral reflection characteristics; then selected cadmium red, cadmium yellow and cobalt blue as the base pigments, which are roughly the same as the natural background-green in the infrared band spectral reflectance curve. Carried out a large number of experiments to prepare several green color samples from pale green, light green, medium green to blackish green and recorded the basic color ratio to construct a basic green pigment formula library according to the color reduction principle of color mixing. Respectively establish a mathematical model of the chromaticity values and the mass ratio of the yellow and blue base pigments, verify the model by using multiple nonlinear regression methods in SPSS, and verify the regression significant effect of the model built. Using the color-difference calculation formula, a nonlinear function model is established, and the minimum point of the function is found by MATLAB neural network genetic algorithm, and the mass ratio of the base pigment of the simulated background color is obtained. The results show that the spectral curve satisfies the requirement of the same-color same-spectrum compared to the background, which can meet the needs of camouflage color matching and provide a scheme for camouflage color matching automation and intelligent.

The exciton complexes in two-dimensional materials have long fascinated scientists and researchers for their mechanisms in fundamental photo-physics. And it is well established that the evolution of defect bound excitons in twodimensional semiconducting TMDs brings largely unexplored opportunities for tailoring their optoelectronic properties. Yet thus far, the properties of defect bound excitons of TMDs have been rarely investigated. In this work, the intrinsic properties of defect bound excitons in aged CVD-grown monolayer WS2 are experimentally studied by the steady-state photoluminescence measurement. Specifically, the photoluminescence mapping experiment is conducted to demonstrate the spatial distribution of the defect bound excitons, whose spectral feature is located ~0.2 eV below the neutral free Aexcitons. Additionally, the power-dependent photoluminescence experiment is applied to investigate the behavior of the defect-state photoluminescence and a significant nonlinear dependence of defect bound excitons on excitation power is revealed. Furthermore, we directly observed the disappearance of defect-state photoluminescence by exposing sample to high laser power irradiation, which can be explained by the enhanced desorption process of molecules physiosorbed on surfaces under laser irradiation. The results of our work provide a comprehensive understanding for the defect bound excitons in monolayer tungsten disulfide, which is essential in promoting the development of defect engineering about two-dimensional semiconducting TMDs and may pave the way for tailoring the performance of the optoelectronic device.

Through the analysis of the various landing modes of the current UAVs, based on the full use of the passive characteristics of visual information, a full visual information guided landing method based on visual sequence images is proposed, and a new color guiding function is designed. Multi-graphic cooperation goal, using the method of air-ground cooperative visual matching, through the selection of cooperative target and the construction process of coordinate system, the specific calculation process of flight attitude information of UAV is described, and the real-time performance of visual information processing during UAV landing process is guaranteed. Under the premise of accuracy and accuracy, the recognition and processing of cooperation targets are completed by means of grayscale transformation, HSV color transformation and HU constant distance matching. The landing mode study provides a valuable reference for the UAV's full visual autonomous landing.

The application of fused silica in the field of High power laser requires that the formation of sub-surface damage be reduced in the process of grinding and polishing. Subsurface damage is unavoidable in traditional processing methods. Laser smoothing, as a non-contact polishing method, has attracted more and more attention in the surface treatment of fused silica. Laser smoothing is capable of producing smooth surface without incurring serious mechanical defects. Thus it is employed to polish fused silica in the hope of reducing mechanical defects on the optical components. In this paper, aiming at the ground surface of fused silica, the characteristics of mid-far infrared laser treatment and modification are studied. The surface smoothness under different laser power are studied, and the optimal laser power and action time for laser smoothing are obtained. This technology can reduce the ground surface roughness from above 100 nanometer to nanometer.

In high power solid-state laser facilities, stray lights may do great damage to optical glass and metal structure and affect the transmission of the main laser and the environment cleanliness inside the facility. On the other hand, the stray may also form noise signal of the main laser pulse and affect the output quality. There are mature solutions for the controlling and absorption of parallel and divergent stray light^[2]. However there are no reliable solution for the absorption of the converging stray light near its focal spot. An absorber design are proposed using multiple materials and small angle light cone. And this design can realize effective absorption of the stray light focal spot with the peak fluence up to 40J/cm2.

All-solid-state (ASS) ultraviolet (UV) laser is an organic combination of ASS laser technique and nonlinear frequency conversion technique. By using different kinds of nonlinear optical crystals and optimizing the system structure, the conversion efficiency and output power of fifth-harmonic-generation (5HG) of ASS lasers has been constantly updated. And the expected UV laser with high beam quality and stability was obtained through reasonable system design. In this paper, the research status of 5HG for ~1 μm near-infrared ASS lasers were briefly reviewed, different approaches for producing 5HG were compared, and the advantages and disadvantages of the corresponding approaches are analyzed.

Photoacoustic imaging is a promising technique that complements ultrasound and is able to distinguish benign from malignant tumors. Higher laser energy results in higher signal-to-noise ratio. Unfortunately, the higher laser energy is more costly and the maximum laser energy is also limited by the maximum permissible exposure imposed by the American National Standards Institute for human skin. The study of interaction of laser with tumorembedded uterine tissue is of great theoretical and practical significance for the laser diagnosis and treatment of endometrial cancer in medicine. In this paper, a 2D tumor-embedded uterine model, which was established by the histological structure of uterus, has been developed incorporating light propagation and heat transfer in soft tissues using a commercial FE simulation package, COMSOL Multiphysics. The light propagation were implemented through the tissues using the diffusion equation. Bioheat transfer in tissues was simulated using Pennes equation for temperature change, and the damage of the tissues was simulated by employing Arrhenius equation. The simulation results show that a cylindrical diffuser can illuminate almost the whole uterus at the same time. The light absorptions of the tumor and the normal tissue are big difference which could result in a high signal-to-noise ratio. Furthermore, the damage of the left side of the tumor is getting worse and irreversible after the laser irradiation. The conclusions are helpful to optimize the laser source and to improve the imaging depth in a photoacoustic imaging system, providing some significance for the further study of the early diagnosis of endometrial cancer.

The damage threshold of CCD’s black and white screen has been effectively measured in this paper. The visible array CCD is a type of photoelectric detector used at the visible wavelengths. The black and white screen of visible array CCD had been observed when it was irradiated by 532nm pulsed laser with low repetition frequency and high energy from a distance of 30m. The measurement method was proposed for the damage threshold of laser power density at the photosensitive surface when the black and white screen came into being. The gain of optical system was firstly designed to measure as 4.4×10³ by changing the repetition frequency of incident laser and adding the right attenuation slices in light path, and finally the damage threshold of CCD’s black and white screen was calculated as 4.5W/cm². The research fruit can provide the theoretical basis and data reference for carrying out the jamming and blinding photoelectric detector of high power laser.

Laser ablation of aluminum alloy and stainless steel were investigated experimentally with a picosecond laser (1053 nm, 8.6 ps, 1Hz). We analyzed and compared the damage threshold and morphology of stainless steel and aluminum alloy. The single-pulse ablation threshold of stainless steel is higher than that of aluminum alloy. The ablation morphology are quite different under multi-pulse irradiation, and the micro-scale periodic surface structures are formed on the stainless steel surface but not on the aluminum alloy sample. The influence of metal thermodynamic properties on laser ablation characteristics is analyzed.

In this paper one novel conjugated enzothiazole derivative doped Polymethyl methacrylate C₁₈H₁₅N₃SFe with D-π-A structures were synthesized to realize reverse saturable absorption (RSA) under femtosecond laser excitation resulting from two-photon absorption (TPA) and TPA-induced excited-state absorption (TPA−ESA). we describe the linear and nonlinear optical (NLO) properties of enzothiazole derivative doped Polymethyl methacrylate C₁₈H₁₅N₃SFe. The nonlinear absorption of Polymethyl methacrylate can be enhanced by enzothiazole derivative doped. The Z-scan results revealed that C₁₈H₁₅N₃SFe/PMMA showed RSA on the femtosecond time regions (532 nm). All the results indicate show that C₁₈H₁₅N₃SFe /PMMA are promising candidates for future optoelectronic and RSA applications.

This paper aims at reducing iron loss of oriented silicon steel and improving its electromagnetic properties. The laser ablation was carried out with different scribe spacing by 532nm picosecond laser. The characteristics of ablation morphology and ablation mechanism were analyzed and discussed using 3D confocal microscope, SEM and EDS. Key magnetic parameters of oriented silicon steel such as relative permeability, dynamic hysteresis loop, and iron loss were measured using iron loss meter. The results show a regular and defect-free ablation morphology obtained by 532nm ultrafast laser, which has the characteristics of force effect damage. The performance improvement effect of silicon steel with the scribe spacing 3.5mm has been shown to be the best. The P_1.5/50 and P_1.7/50 decreased by 11.5% and 13.8% respectively, the peak of relative permeability increased by 13.6%, and the coercivity and loop area decreased by 12.3% and 11.9% respectively. The improvement of magnetic properties of silicon steel mainly depends on the domain structure and residual stress distribution.

In order to analyze the thermal damage process under high energy laser irradiation, this paper focused on the high temperature condition and designed experimental device for coatings heating at different temperature. Ellipsometer was applied to measure the ellipsometric parameter (Ψ, ▵) of SiO₂, HfO₂ and Al₂O₃ single layer (prepared by electron beam (EB) evaporation on BK7 glass) at different temperatures, so the variation of optical constants with temperatures was obtained by inversion calculation. With the increase of temperature, the refractive index (n) of SiO₂, HfO₂ and Al₂O₃ single layer first decreased and then increased, the thickness (d) of these layers first increase and then decreased. However, the inflection point occurred at different temperature, and the amount of change was different for the layer with different material. The physical processes of thermal expansion and water evaporation were applied to explain the temperature dependent properties of the dielectric coatings.

The change of surface roughness of modified silicon carbide during ion beam polishing is introduced in this paper. Silicon carbide has been gradually applied to laxer mirrors due to its excellent physical properties. Ion beam polishing is a high precision and high certainty processing method, but it is not suitable to directly process silicon carbide body due to material reasons. First, the silicon carbide substrate material was modified by ion beam assisted deposition of silicon, and then the relationship between the depth of ion beam removal and the surface roughness evolution experiment was carried out. The experiment was divided into two stages. The first stage was to verify the quality of the modified layer, after a large number of processing and removal, to detect the change of the modified layer; the second stage was to find the change rule of the roughness, by adjusting the ion beam addition. In order to control the trend of roughness the basis of experiments, a Ф600mm modified silicon carbide plane mirror was fabricated by ion beam polishing. After two iterations, the processing results show that the surface roughness of the sample can be controlled within 2 nanometers(Sq value)by adjusting the processing strength and removal depth.

Optical film damage threshold is an important basis for measuring the ability of film to resist laser damage, and laser parameters are the key factors affecting its accurate measurement. The single-factor control variable method was used to establish the the numerical model of laser energy error, the focused spot size error and the damage threshold error, and the M ² factor and the damage threshold. The theoretical analysis and computer simulation of the energy error, the focused spot size error and the beam quality on the film damage threshold influences. A method based on the Shack-Hartman wave-front detection method is proposed to measure the pulsed laser beam parameters. The working principle is described in detail, and the Shack-Hartman beam shape parameter measurement system is designed. The actual output energy of the laser and the size of the focused spot were measured experimentally, and the uncertainty of the film damage threshold was evaluated according to the statistical principle. The results shows that the energy error and the focused spot error are directly proportional to the damage threshold error, and M ² is inversely related to the damage threshold. From the thin film sample analysis, the relative uncertainty of the damage threshold measurement is 18.78%. Therefore, studying the influence of laser parameters on the damage threshold provides a direction for obtaining accurate film damage threshold test results.

Subsurface micro-cracks will be generated during the grinding and polishing processes of optical components. Microcracks have a modulation effect on the laser, thereby reducing the laser damage threshold. The FDTD method is used to simulate the light intensity distribution modulated by micro-crack. By comparing the simulation results of radial crack, parabolic crack and elliptic crack, the modulation mechanism of micro-crack is revealed. The results show that for the crack with the same width and depth, light intensity enhancement factor (LIEF) modulated by radial crack on the rear surface and parabolic crack on the front surface is the largest; LIEF modulated by elliptical crack on the rear surface and radial crack on the front surface is the smallest. In addition, when the crack width-depth ratio is the same, the larger the depth, the higher the LIEF. As the width-depth ratio increases, the LIEF value increases firstly, then decreases, and finally approaches a stable value.

The accumulation effects in high-reflectivity (HR) HfO₂/SiO₂ coatings under laser irradiation at different laser wavelengths are investigated respectively. It was found that the multi-shot laser induced damage thresholds (LIDTs) were always lower than that under single-shot at 1064 nm and 532 nm because of "fatigue effect". And the evolution of LIDTs versus shot number, namely the optic lifetime was acquired. The previous analysis verified the accumulation damage mechanism was mainly due to the influence of newly created defects, namely, the laser-induced defects or intrinsic defects with irreversible changes under multiple pulse irradiations. Thus, a correlative theory model based on critical conduction band electron density is constructed to elucidate the experimental phenomena in nanosecond at different wavelengths with a 5Hz repetition rate. In particular, shallow trap (defect state) of varying absorption crosssection with irradiated shot numbers is used to simulate the material modification process under multiple pulse irradiations. It’s found that the absorption cross-section of the defect state at 532 nm is about one order of magnitude higher than that at 1064 nm, and defects at 532 nm need much less shot numbers to reach saturation with a higher growth factor.

Publisher’s Note: This paper, originally published on 8 July 2019, was replaced with a corrected/revised version on 13 August 2019. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.