- 标题
- 摘要
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- 实验方案
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Effect of temperature fields on optical properties of La <sub/>2</sub> Ti <sub/>2</sub> O <sub/>7</sub> thin films
摘要： In order to study the effect of temperature ?elds on the microstructure, optical properties and response to laser damage of La2Ti2O7 ?lms, a group of ?lms were prepared by electron beam evaporation using the same parameters on Si and fused silica substrates. Then, rapid thermal annealing at different temperatures was applied to simulate the application of a temperature ?eld. The structure, optical constants and response to laser damage of La2Ti2O7 ?lms were investigated by XPS, XRD, ellipsometry and laser damage testing. The results showed that Ti4+ is gradually converted to Ti3+ with increasing temperature resulting in a higher refractive index, larger extinction coef?cient and more serious absorption. When the temperature was higher than 800 °C, the loss of oxygen was more pronounced. The density of annealed ?lms ?rst increased and then decreased when the temperature rises from 600 to 1000 °C, and reached its maximum at 800 °C. And the crystallization, oxygen loss and densi?cation were found to be related to the laser damage threshold of La2Ti2O7 ?lm. The laser damage threshold of the ?lm decreased sharply when the temperature is above 900 °C.
关键词： temperature ?eld,optical properties,La2Ti2O7 ?lm,laser-induced damage
更新于2025-09-23 15:21:21
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[Lecture Notes in Computer Science] Pattern Recognition and Computer Vision Volume 11256 (First Chinese Conference, PRCV 2018, Guangzhou, China, November 23-26, 2018, Proceedings, Part I) || Damage Online Inspection in Large-Aperture Final Optics
摘要： Under the condition of inhomogeneous total internal reflection illumination, a novel approach based on machine learning is proposed to solve the problem of damage online inspection in large-aperture final optics. The damage online inspection mainly includes three problems: automatic classification of true and false laser-induced damage (LID), automatic classification of input and exit surface LID and size measurement of the LID. We first use the local area signal-to-noise ratio (LASNR) algorithm to segment all the candidate sites in the image, then use kernel-based extreme learning machine (K-ELM) to distinguish the true and false damage sites from the candidate sites, propose autoencoder-based extreme learning machine (A-ELM) to distinguish the input and exit surface damage sites from the true damage sites, and finally propose hierarchical kernel extreme learning machine (HK-ELM) to predict the damage size. The experimental results show that the method proposed in this paper has a better performance than traditional methods. The accuracy rate is 97.46% in the classification of true and false damage; the accuracy rate is 97.66% in the classification of input and exit surface damage; the mean relative error of the predicted size is within 10%. So the proposed method meets the technical requirements for the damage online inspection.
关键词： Size measurement,Damage online inspection,Classification,Laser-induced damage,Machine learning
更新于2025-09-23 15:21:01
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Different material modifications in laser-induced damage of optical films in air and vacuum environments
摘要： A combination study of material modifications for the catastrophic laser-induced damage by 12 ns, 1064 nm laser pulse irradiation was investigated in air and vacuum environments. The samples were observed by optical microscope, scanning electron microscopy, laser micro-Raman spectroscopy, photoluminescence spectrum; moreover 2D numerical calculations were performed. According to our results, vacuum pumping induced higher laser field intensities, accompanying with more absorption of laser energy in the laser-induced damage process. All of these resulted in the material melting and subsequent re-solidification in the laser-damaged core in vacuum. While, in the air conditions, plasma expanding due to material heating and associated thermal expansion induced a large stress field, which caused the material deformation and formation of delamination and crack in the laser-damage region.
关键词： Vacuum,Photoluminescence spectrum,Laser-induced damage,Laser micro-Raman spectroscopy
更新于2025-09-23 15:21:01
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Development of a defect recognition algorithm for visual laser-induced damage detection
摘要： Laser-induced damage is defined as a permanent detrimental change in the characteristics of an optical element caused by a laser beam. This change can be observed by many different inspection techniques, of which optical and phase imaging microscopic techniques have superior sensitivity. However, such examinations conducted by human operators are relatively slow and subjective—so they cannot be used for online damage monitoring purposes, whereas automatic inspection systems have advantages in terms of sensitivity, reliability, and speed. In this paper we introduce a new method for the computer-aided recognition of damaged sites based on visual images taken from the sample surface by a CCD camera. The evaluation procedure is performed by a computer algorithm, which consists of exact, statistically established steps. It includes noise reduction by considering the statistical behavior of photon noise. Besides, it takes into account the spatial extent of a damage spot by nonlinear image filtering to separate damage-indicating intensity changes from random noise. This mimics the ability of the human eye to distinguish features from their surroundings. The evaluation algorithm is built of computationally less demanding mathematical operations to enable fast execution which is vital for monitoring at high repetition rates. The proposed method was tested on a sizeable dataset of images yielding 98.8% of damage detection efficiency. It was also compared to a generally used visual laser damage detection procedure, which has a success rate of 88.6%. This yields one order of magnitude reduction in the number of undetected damaged sites.
关键词： image filter,Chebyshev’s theorem,laser-induced damage,machine vision,poisson noise
更新于2025-09-23 15:21:01
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Optical characteristics of the undamaged and laser damaged K9 glass in terahertz band
摘要： K9 glass is an important optical element of the high energy laser system. In an attempt to investigate the variation of optical properties of K9 glass before and after laser induced damage, based on the transmission terahertz time-domain spectral system, the undamaged and the damaged K9 glasses induced by laser were tested to obtain the terahertz time-domain and frequency-domain spectra and the refractive index and absorption coef?cient of the samples were calculated in terahertz band for further analysis. Results show that with the increase of laser energy, from the undamaged to the damaged K9 glasses to different extent, the peak to peak value in time domain and the amplitude value in frequency domain present a decreasing trend in varying degrees, and in the 0.4～0.5 THz band, the absorption coef?cient increases continuously with a slight change of refractive index, which indicates that K9 glass not only appears the melting and fracture in the macroscopic morphology after laser-induced damage, but also forms non-bridged oxygen atoms in its microstructure with more ion bonds and free electrons and the change of ion polarization. In this regard, this paper provides a technical basis for exploring the micro characteristics of K9 glass after laser-induced damage, and lays a good foundation for the application of terahertz time-domain spectroscopy to laser-induced damage analysis.
关键词： terahertz time-domain spectrum,K9 glass,laser-induced damage,refractive index,absorption coef?cient
更新于2025-09-23 15:21:01
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Study of Thermal Effect in the Interaction of Nanosecond Capillary Discharge Extreme Ultraviolet Laser with Copper
摘要： Interaction of Extreme Ultraviolet (EUV) laser with matters is an attractive subject since novel phenomena always occur under the e?ect of high energy photons. In this paper, the thermal e?ect involved in the interaction of a capillary discharge 46.9 nm laser with copper was studied theoretically and experimentally. The temperature variation of the laser-irradiated region of copper was calculated. According to the results, the copper surface was ablated obviously and presented the trace of melting, evaporation, and resolidi?cation, which suggested the thermal e?ect occurred on the surface during the laser irradiation.
关键词： laser-induced damage,thermal e?ect,copper,46.9 nm laser
更新于2025-09-23 15:19:57
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Difference in laser-induced damage behavior between back and front surfaces
摘要： When nanosecond-pulsed laser induces transmission element damage, the coupling effect of plasma and laser affects the damage process of the back and front surfaces, thereby determining the final damage morphology. This study presents the effects on the suppression and enhancement of plasma on particle ejection, the intensity of laser absorption and obstruction, and the surface morphology and drilling efficiency of multi-pulse laser processing. The difference between the back and front surface damage was compared, and the causes and function process were analyzed. Experiments are helpful to understand the role of plasma and the difference in damage between the back and front surfaces so that the thermal mechanism damage is clarified.
关键词： plasma,back and front surface,laser-induced damage,particle ejection
更新于2025-09-23 15:19:57
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Dynamic behavior modeling of laser-induced damage initiated by surface defects on KDP crystals under nanosecond laser irradiation
摘要： the issue of laser-induced damage of transparent dielectric optics has severely limited the development of high-power laser systems. exploring the transient dynamic behaviors of laser damage on KDp surface by developing multi-physics coupling dynamics model is an important way to reveal the mechanism of nanosecond laser damage. In this work, KDP crystals are taken as an example to explore the mechanism of laser-induced surface damage. Based on the theories of electromagnetic field, heat conduction and fluid dynamics, a multi-physics coupling dynamics model is established for describing the evolution of nanosecond damage processes. The dynamics of laser energy transmission, thermal field distribution and damage morphology during nanosecond laser irradiation are simulated with this model. 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 temperature field and crater morphology during subsequent laser irradiation is helpful to understand the laser damage process. The feasibility of this model is verified by the morphology information of typical defect-induced laser damage. this work provides further insights in explaining the laser-induced damage by surface defects on KDp crystals. the model can be also applied to investigate the laser damage mechanisms of other transparent dielectric optics.
关键词： laser-induced damage,multi-physics coupling model,nanosecond laser irradiation,KDP crystals,surface defects
更新于2025-09-19 17:13:59
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Nanosecond laser-induced surface damage and its mechanism of CaF2 optical window at 248a??nm KrF excimer laser
摘要： Calcium fluoride (CaF2) crystals is a kind of important optical material for ultraviolet (UV) and deep-ultraviolet (DUV) lithography and high-power laser-related applications. However, its laser-induced damage threshold (LIDT) directly affects the laser power, so that the above-mentioned applications could be limited. Therefore, the research on the damage characteristics and laser damage resistance of caf2 crystals is urgent. A 3D Finite-Difference Time-Domain (FDTD) method with Maxwell spinor equation is used, and the results show that the electric field intensity of rear surface is larger than that of front surface, which causes a lower threshold and is consistent with the experimental observations. And a thermo-mechanical coupled finite element model (FEM) of CaF2 with ce2o3 impurities, which are introduced by polishing process, has semiquantitatively described the damage mechanism of CaF2 by 248 nm-excimer laser.
关键词： laser-induced damage,FDTD,CaF2,FEM,ultraviolet excimer laser
更新于2025-09-19 17:13:59
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High-repetition-rate laser-induced damage of indium tin oxide films and polyimide films at a 1064 nm wavelength
摘要： Experiments and thermal modeling of indium tin oxide transparent conductive thin film and polyimide alignment thin film coated on fused silica substrates damaged with a 1064 nm high-repetition-rate laser are described. High-repetition-rate laser irradiation results in damaged morphologies of the bulge at low laser power density and formation of a pit in the center of the bulge at higher laser power density. The damage process that is consistent with the observations as a function of laser power density and irradiation time is related to thermal effect. Simulation of the temperature-rise by exposure to high-repetition-rate laser describes the thermal effect with different pulse oscillation.
关键词： high-repetition-rate laser,polyimide,laser-induced damage,thermal modeling,indium tin oxide
更新于2025-09-19 17:13:59