Laser-induced damage on large-aperture fused silica gratings

Two sets of laser-damage experiments on large-aperture fused silica optics have been carried out in a high-power laser facility. Severe damage has been found on the grating which presented dense craters on the front surface. This phenomenon is quite different from other fused silica optics, which are damaged on the rear surface. The damage possibility due to the redeposition layer was ruled out by acid-etching the grating＇s front surface. The remarkable stimulated Brillouin scattering （SBS） effect was observed in grating and the reason for the front surface damage is thought to be the backward SBS.

Characteristics of Laser-Induced Surface and Bulk Damage of Large-Aperture Deuterated Potassium Dihydrogen Phosphate at 351 nm

Deuterated potassium dihydrogen phosphate damage performance at 351 nm is studied on a large-aperture laser system. Bulk and rear-surface damage are initiated under the 3ω fluences of 6.T J/cm2 and 33/cm2, and show different growth characteristics under multiple laser irradiations with the fluence of 6 J/cm2. The size and number of bulk damage keep unchanged once initiated. However, surface damage size also does not grow, while surface damage number increases linearly with laser shots. Different damage thresholds and growth behaviors suggest different formations of bulk and surface damage precursors. The cause of surface damage is supposed to be near-surface absorbing particles buried under the sol-gel coating.

Subsurface defect characterization and laser-induced damage performance of fused silica optics polished with colloidal silica and ceria

This paper mainly focuses on the influence of colloidal silica polishing on the damage performance of fused silica optics. In this paper, nanometer sized colloidal silica and micron sized ceria are used to polish fused silica optics. The colloidal silica polished samples and ceria polished samples exhibit that the root-mean-squared （RMS） average surface roughness values are 0.7 nm and 1.0 rim, respectively. The subsurface defects and damage performance of the polished optics are analyzed and discussed. It is revealed that colloidal silica polishing will introduce much fewer absorptive con- taminant elements and subsurface damages especially no trailing indentation fracture. The 355-nm laser damage test reveals that each of the fused silica samples polished with colloidal silica has a much higher damage threshold and lower damage density than ceria polished samples. Colloidal silica polishing is potential in manufacturing high power laser optics.

Laser-induced damage threshold in HfO_2/SiO_2 multilayer films irradiated by β-ray

Post-processing can effectively improve the resistance to laser damage in multilayer films used in a high power laser system. In this work, HfO_2/SiO_2 multilayer films are prepared by e-beam evaporation and then β-ray irradiation is employed as the post-processing method. The particle irradiation affects the laser induced damage threshold(LIDT),which includes defects, surface roughness, packing density and residual stress. The residual stress that is relaxed during irradiation changes from compressive stress into tensile stress. Our results indicate that appropriate tensile stress can improve LIDT remarkably. In view of the fact that LIDT rises from 8 J/cm^2 to 12 J/cm^2, i.e., 50% increase, after the film has been irradiated by 2.2×10^(13)/cm^2 β-ray, the particle irradiation can be used as a controllable and desirable postprocessing method to improve the resistance to laser induced damage.

Microstructure and 355 nm Laser-Induced Damage Characteristics of Al₂O₃Films Irradiated with Oxygen Plasma under Different Energy

Al2O3 films were prepared using electron beam evaporation at room temperature. The samples were irradiated with oxygen plasma under different energy. The variations in average surface defect density and root mean square (RMS) surface roughness were characterized using an optical microscope and an atomic force microscope. Surface average defect density increased after plasma treatment. The RMS surface roughness of the samples decreased from 1.92 nm to 1.26 nm because of surface atom restructuring after oxygen plasma conditioning. A 355 nm laser-induced damage experiment indicated that the as-grown sample with the lowest defect density exhibited a higher laser-induced damage threshold (1.12 J/cm2) than the other treated samples. Laser-induced damage images revealed that defect is one of the key factors that affect laser-induced damage on Al2O3 films.

Effect of EGb761 on light-damaged retinal pigment epithelial cells

AIM: To investigate the protective mechanism of Gingko Biloba extract(EGb761) on the ability of retinal pigment epithelial(RPE) cells to resist light-induced damage in a comparative proteomics study. · METHODS: Human RPE cells(ARPE-19) were randomly distributed to one of three groups: normal control(NC group) and light-damaged model without or with EGb761 group(M and ME groups,respectively). The light-damaged model was formed by exposing to white light(2 200 ±300)lx for 6h. The RPE cells in ME group were conducted with EGb761(100μg/mL) before light exposure. The soluble cellular proteins extracting from each groups were separated by two-dimensional electrophoresis and stained by silver staining. Different proteins in the profiles of the gels were analyzed by Image Master Software. Two-fold expressing protein spots were identified by Matrix-assisted laser desorption/ ionization tandem time-of-flight(MALDI-TOF/TOF) mass spectrometry. ·RESULTS: NC,M and ME groups displayed 1 892±71,2 145 ±23 and 2 216 ±85 protein spots,respectively. We identified 33 proteins with different expression levels between the NC and M groups,25 proteins between the M and ME groups,and 11 proteins between the NC and ME groups. MALDI-TOF/TOF mass spectrometry successfully identified 16 proteins,including metabolic enzymes,cytoskeletal proteins,anti-oxidation proteins,and others. ·CONCLUSION: Differences in some important proteins,such as cathepsin B,heat shock protein,and cytochrome C reductase,indicated that multiple pathways may be induced in light-damaged RPE cells and the protective effect of EGb761.

Correlation of polishing-induced shallow subsurface damages with laser-induced gray haze damages in fused silica optics

Laser-induced damage in fused silica optics greatly restricts the performances of laser facilities. Gray haze damage,which is always initiated on ceria polished optics, is one of the most important damage morphologies in fused silica optics.In this paper, the laser-induced gray haze damages of four fused silica samples polished with CeO2, Al2O3, ZrO2, and colloidal silica slurries are investigated. Four samples all present gray haze damages with much different damage densities.Then, the polishing-induced contaminant and subsurface damages in four samples are analyzed. The results reveal that the gray haze damages could be initiated on the samples without Ce contaminant and are inclined to show a tight correlation with the shallow subsurface damages.

The effect of laser beam size on laser-induced damage performance

The influence of laser beam size on laser-induced damage performance, especially damage probability and the laser-induced damage threshold （LIDT）, is investigated. It is found that damage probability is dependent on beam size when various damage precursors with different potential behaviors are involved. This causes the damage probability and the LIDT to be different between cases under a large-apertnre beam and a small-aperture beam. Moreover, the fluenee fluctuation of the large-aperture laser beam brings out hot spots, which move randomly across the beam from shot to shot. Thus this leads the most probable maximum fluenee after many shots at any location on the optical component to be several times the average beam fluence, These two effects result in the difference in the damage performance of the optical component between the cases under a large-aperture and small-aperture laser.

Vitreous hemorrhage and fibrovascular proliferation after laser-induced chorioretinal venous anastomosis

·AIM:To describe a case in which vitrectomy was required for vitreous hemorrhage and fibrovascular proliferation after laser-induced chorioretinal venous anastomosis (LCVA) for non-ischemic central retinal vein occlusion (CRVO).·METHODS:Observational case report.·RESULTS:A 72-year-old man complained of central scotoma in the left eye,and was diagnosed as suffering from non-ischemic CRVO.LCVA was performed in another hospital.Although favorable visual function was briefly maintained postoperatively,severe vitreous hemorrhage developed in his left eye,necessitating vitrectomy.·CONCLUSION:Considering that LCVA carries a risk of serious complications,we must apply this treatment with caution,especially in ethnic groups,such as the Japanese,in whom pigmentation reacts to photocoagulation excessively.·

Editor's Choice——Retinal ganglion cell damage and regeneration

Retinal ganglion cell apoptosis is considered to be the main cause of loss of vision in glaucoma patients. Microglia cells are phagocytic cells present in the retina. In the retina of glaucoma rat models, microglia cells become activated, which suggests a role for microglia in the pathogenesis of optic nerve injury in glaucoma patients. The retinal ganglion cell is the only cell that can produce action potential in the retina,

Laser-induced Damage of 355 nm High-reflective Mirror Caused by Nanoscale Defect

Al2O3/SiO2 multilayer high-reflective（HR） mirrors at 355 nm were prepared by electron beam evaporation, and post-irradiated with Ar/O mixture plasma. The surface defect density, reflective spectra, and laser-induced damage characteristics were measured using optical microscopy, spectrophotometry, a damage testing system, and scanning electron microscopy（SEM）, respectively. The results indicated that moderate-time of irradiation enhanced the laser-induced damage threshold（LIDT） of the mirror, but prolonged irradiation produced surface defects, resulting in LIDT degradation. LIDT of the mirrors initially increased and subsequently decreased with the plasma processing time. SEM damage morphologies of the mirrors revealed that nanoscale absorbing defects in sub-layers was one of the key factors limiting the improvement of LIDT in 355 nm HR mirror.

Non-blind super-resolution reconstruction for laser-induced damage dark-field imaging of optical elements

The laser-induced damage detection images used in high-power laser facilities have a dark background,few textures with sparse and small-sized damage sites,and slight degradation caused by slight defocus and optical diffraction,which make the image superresolution(SR)reconstruction challenging.We propose a non-blind SR reconstruction method by using an exquisite mixing of high-,intermediate-,and low-frequency information at each stage of pixel reconstruction based on UNet.We simplify the channel attention mechanism and activation function to focus on the useful channels and keep the global information in the features.We pay more attention on the damage area in the loss function of our end-toend deep neural network.For constructing a high-low resolution image pairs data set,we precisely measure the point spread function(PSF)of a low-resolution imaging system by using a Bernoulli calibration pattern;the influence of different distance and lateral position on PSFs is also considered.A high-resolution camera is used to acquire the ground-truth images,which is used to create a low-resolution image pairs data set by convolving with the measured PSFs.Trained on the data set,our network has achieved better results,which proves the effectiveness of our method.

Continuous gradient fusion class activation mapping: segmentation of laser-induced damage on large-aperture optics in dark-field images

Segmenting dark-field images of laser-induced damage on large-aperture optics in high-power laser facilities is challenged by complicated damage morphology, uneven illumination and stray light interference. Fully supervised semantic segmentation algorithms have achieved state-of-the-art performance but rely on a large number of pixel-level labels, which are time-consuming and labor-consuming to produce. LayerCAM, an advanced weakly supervised semantic segmentation algorithm, can generate pixel-accurate results using only image-level labels, but its scattered and partially underactivated class activation regions degrade segmentation performance. In this paper, we propose a weakly supervised semantic segmentation method, continuous gradient class activation mapping(CAM) and its nonlinear multiscale fusion(continuous gradient fusion CAM). The method redesigns backpropagating gradients and nonlinearly activates multiscale fused heatmaps to generate more fine-grained class activation maps with an appropriate activation degree for different damage site sizes. Experiments on our dataset show that the proposed method can achieve segmentation performance comparable to that of fully supervised algorithms.

The compatibly large nonlinear optical effect and high laser-induced damage threshold in a thiophosphate CsInP_(2)S_(7)constructed with[P_(2)S_(7)]^(4-)and[InS_(6)]^(9-)

It is challenging to cooperatively improve the nonlinear optical(NLO)efficiency and the laser-induced damage threshold(LIDT).This work reports a novel IR NLO materials CsInP_(2)S_(7)(CIPS)designed by combination the strategies of alkali metals substitution and microscopic NLO units PS4 introduction based on AgGaS_(2).CIPS was composed of strongly distorted[InS_(6)]^(9-)octahedra and[P_(2)S_(7)]4-dimers constructed by corner-sharing[PS_(4)]^(3-),which increase the NLO efficiency and decrease thermal expansion anisotropy simultaneously.Compared with AgGaS_(2),CIPS exhibited strong phase matchable NLO response ca.1.1×AGS@2.1μm,high LIDT ca.20.8×AgGaS_(2),and IR transparency up to 15.3μm.Structural analysis and theoretical investigation confirmed that large SHG effect and ultrahigh LIDT of CIPS originated from the synergistic contribution of[InS_(6)]^(9-)octahedra and[P_(2)S_(7)]4-dimers.These results indicate that CIPS is a promising NLO candidate in the mid-IR region,and this study provides a new approach for developing potential NLO-LIDT compatible materials.

Incident laser modulation of a repaired damage site with a rim in fused silica rear subsurface

Local CO2 laser treatment has proved to be an effective method to prevent the 351-nm laser-induced damage sites in a fused silica surface from exponentially growing, which is responsible for limiting the lifetime of optics in high fluence laser systems. However, the CO2 laser induced ablation crater is often surrounded by a raised rim at the edge, which can also result in the intensification of transmitted ultraviolet light that may damage the downstream optics. In this work, the three-dimensional finite-difference time-domain method is developed to simulate the distribution of electrical field intensity in the vicinity of the CO2 laser mitigated damage site located in the exit subsurface of fused silica. The simulated results show that the repaired damage sites with raised rims cause more notable modulation to the incident laser than those without rims.Speeifically,we present a theoretical model of using dimpled patterning to control the rim structure around the edge of repaired damage sites to avoid damage to downstream optics. The calculated results accord well with previous experimental results and the underlying physical mechanism is analysed in detail

Numerical simulation of the modulation to incident laser by the repaired damage site in a fused silica subsurface

One of the main factors of laser induced damage is the modulation to incident laser which is caused by the defect in the subsurface of the fused silica. In this work, the repaired damage site irradiated by CO2 laser is simplified to a Gaussian rotation according to the corresponding experimental results. Then, the three-dimensional finite-difference time-domain method is employed to simulate the electric field intensity distribution in the vicinity of this kind of defect in fused silica front subsurface. The simulated results show that the modulation is notable, the Emax is about 2.6 times the irradiated electric field intensity in the fused silica with the damage site （the width is 1.5 μm and depth is 2.3 μm） though the damage site is repaired by CO2 laser. The phenomenon and the theoretical result of the annular laser enhancement existed on the rear surface are first verified effectively, which agrees well with the corresponding experimental results. The relations between the maximal electric field intensity in fused silica with defect depth and width are given respectively. Meanwhile, the corresponding physical mechanism is analysed theoretically in detail.

Time-dependent photothermal characterization on damage of fused silica induced by pulsed 355-nm laser with high repetition rate

Time-dependent damage to fused silica induced by high frequency ultraviolet laser is investigated.Photothermal spectroscopy(PTS) and optical microscopy(OM) are utilized to characterize the evolution of damage pits with irradiation time.Experimental results describe that in the pre-damage stage of fused silica sample irradiated by 355-nm laser,the photothermal spectrum signal undergoes a process from scratch to metamorphism due to the absorption of laser energy by defects.During the visible damage stage of fused siliea sample,the photothermal spectrum signal decreases gradually from the maximum value because of the aggravation of the damage and the splashing of the material.This method can be used to estimate the operation lifetime of optical elements in engineering.

Characteristics of Optic Nerve Damage Induced by Chronic Intraocular Hypertension in Rat

Purpose:To set up the Sharma’s chronic intraocular hypertension model and investigate the intraocular pressure (IOP) as well as the optic nerve damage of this model in rat. Methods:The operations of the chronic intraocular hypertension model were performed as described by Sharma in 60 male Lewis albino rats. IOP was measured using the Tono-Pen XL immediately after surgery and then at 5 day, 2 week or 4 week intervals. Cresyl violet staining of whole-mounted retinas was used to label retinal ganglion cells (RGCs), then RGCs were counted. Paraphenylenediamine (PPD) staining was performed in the semi-thin cross sections of optic nerve of rat, in order to know whether the axons of optic nerve were degenerated or not. Results:There were 47 rats with higher IOP after the episcleral veins cauterized in 60 rats. The ratio of elevated IOP was 78.3%. The IOPs were stable in 4 weeks. After cresyl violet staining, the RGCs loss was 11.0% and 11.3% was found in the central and peripheral retina respectively after 2 weeks of increased IOP. After 4 weeks of increased IOP, the loss of RGCs was 17% for the central retina and 24.6% for the peripheral retina. In the retinas without higher IOP, there was no loss of RGCs. PPD staining showed that optic nerve of rat with about 5.3% damage of axons located at the superior temporal region. Region of affected optic nerve 1 mm posterior to the globe by light microscope showed evidence of damaged axons with axonal swelling and myelin debris. Conclusion:Sharma’s chronic intraocular hypertension model is a reproducible and effective glaucoma model, which mimics human glaucoma with chronically elevation IOP and induced RGCs loss and damage of optic nerve. Eye Science 2004;20:25-29.

Damage threshold influenced by polishing imperfection distribution under 355-nm laser irradiation

A systematic interpretation of laser-induced damage in the nanosecond regime is realized with a defect distribution buried inside the redeposited layer arising from a polishing process. Under the 355-nm laser irradiation, the size dependence of the defect embedded in the fused silica can be illustrated through the thermal conduction model. Considering CeO2 as the major initiator, the size distribution with the power law model is determined from the damage probability statistics. To verify the accuracy of the size distribution, the ion output scaling with depth for the inclusion element is obtained with the secondary ion mass spectrometer. For CeO2 particulates in size of the depth interval with ion output satisfied in the negative exponential form, the corresponding density is consistent with that of the identical size in the calculated size distribution. This coincidence implies an alternative method for the density analysis of photoactive imperfections within optical components at the semi-quantitative level based on the laser damage tests.

Experimental model of photo-oxidative damage

Background:Retinal degeneration is a common feature of several retinal diseases,such as retinitis pigmentosa and age-related macular degeneration(AMD).In this respect,experimental models of photo-oxidative damage reproduce faithfully photoreceptor loss and many pathophysiological events involved in the activation of retinal cell degeneration.Therefore,such models represent a useful tool to study the mechanisms related to cell death.Their advantage consists in the possibility of modulating the severity of damage according to the needs of the experimenter.Indeed,bright light exposure could be regulated in both time and intensity to trigger a burst of apoptosis in photoreceptors,allowing the study of degenerative mechanisms in a controlled fashion,compared to the progressive and slower rate of death in other genetic models of photoreceptor degeneration.Methods:Here,an exemplificative protocol of bright light exposure in albino rat is described,as well as the main outcomes in retinal function,photoreceptor death,oxidative stress,and inflammation,which characterize this model and reproduce the main features of retinal degeneration diseases.Discussion:Models of photo-oxidative damage represent a useful tool to study the mechanisms responsible for photoreceptor degeneration.In this respect,it is important to adapt the exposure paradigm to the experimental needs,and the wide range of variables and limitations influencing the final outcomes should be considered to achieve proper results.Trial Registration:None.