Laser Damage Experiments Research Articles

Nanosecond-level second-order characteristics in dynamic calibration of thin film thermocouples by short-pulse laser

In this study, we explore the dynamic response of thin-film thermocouples (TFTCs) to transient temperature changes, emphasizing their nanosecond response capabilities. Traditionally, TFTCs are modeled as first-order systems. By employing magnetron sputtering, we have prepared NiCr/NiSi TFTCs with a novel integrated lead method. A 7.6 ns short-pulse laser served as the heat source, capturing the TFTCs’ transient response with a high-speed collector at 200 M/s. Unexpectedly, the TFTCs’ response curves exhibited oscillations at high acquisition rates. Through frequency response analysis, we have established a pulse response model for the TFTCs that is highly consistent with experimental results. For the first time, we confirmed the TFTCs’ second-order dynamic characteristics. Furthermore, our findings that various substrate materials and lead methods impact the damping characteristics of TFTCs led us to conduct pulsed laser damage experiments. These experiments revealed a correlation between damping properties and the extent of damage.

Dazzling Evaluation of the Impact of a High-Repetition-Rate CO2 Pulsed Laser on Infrared Imaging Systems.

This article utilizes the Canny edge extraction algorithm based on contour curvature and the cross-correlation template matching algorithm to extensively study the impact of a high-repetition-rate CO2 pulsed laser on the target extraction and tracking performance of an infrared imaging detector. It establishes a quantified dazzling pattern for lasers on infrared imaging systems. By conducting laser dazzling and damage experiments, a detailed analysis of the normalized correlation between the target and the dazzling images is performed to quantitatively describe the laser dazzling effects. Simultaneously, an evaluation system, including target distance and laser power evaluation factors, is established to determine the dazzling level and whether the target is recognizable. The research results reveal that the laser power and target position are crucial factors affecting the detection performance of infrared imaging detector systems under laser dazzling. Different laser powers are required to successfully interfere with the recognition algorithm of the infrared imaging detector at different distances. And laser dazzling produces a considerable quantity of false edge information, which seriously affects the performance of the pattern recognition algorithm. In laser damage experiments, the detector experienced functional damage, with a quarter of the image displaying as completely black. The energy density threshold required for the functional damage of the detector is approximately 3 J/cm2. The dazzling assessment conclusions also apply to the evaluation of the damage results. Finally, the proposed evaluation formula aligns with the experimental results, objectively reflecting the actual impact of laser dazzling on the target extraction and the tracking performance of infrared imaging systems. This study provides an in-depth and accurate analysis for understanding the influence of lasers on the performance of infrared imaging detectors.

Estimation of laser-induced damage depth from surface image features.

In laser damage experiments, damage initiation and growth are typically monitored by imaging the surface of the tested fused silica sample, ignoring their bulk morphology. The depth of a damage site in fused silica optics is considered to be proportional to its equivalent diameter. However, some damage sites experience phases with no diameter changes but growth in the bulk independently from their surface. A proportionality relationship with the damage diameter does not accurately describe the growth of such sites. In the following, an accurate estimator for damage depth is proposed, which is based on the hypothesis that the light intensity scattered by a damage site is proportional to its volume. Such an estimator, using the pixel intensity, describes the change of damage depth through successive laser irradiations, including phases in which depth and diameter variations are uncorrelated.

Laser damage evolution by defects on diamond fly-cutting KDP surfaces

The unavoidable surface defects on the practical processed potassium dihydrogen phosphate (KDP) crystals, especially the most common protuberance defects, which are prone to damage under intense laser irradiation, seriously limit the application of KDP optics in laser fusion facilities. In this work, a defect-induced laser damage explosion model that couples the electromagnetic field and stress field was constructed to reproduce the dynamic damage process and reveal the laser-induced damage mechanisms innovatively. First, the near-field optical modulation to incident lasers was considered to describe the effect of structural parameters of surface defects on the optical transmission performance. A multi-physics field coupled failure model was then established for the first time to explore the laser damage mechanism through the dynamic behaviors of laser damage that reproduced by this model. It was proved that the protuberance defects on KDP crystal surface would lead to severe laser damage with the characteristics of large transverse spalling and longitudinal cracks due to the Rayleigh and stress waves, which well agrees with the results of laser damage experiments. The established damage model is capable of revealing the hazards of protuberance defects, and providing effective guidance for the suppression of surface defects introduced in the optical ultra-precision machining processes.

KrF excimer laser induced damage and its mechanism of CaF2 single crystal with (1 1 1), (1 1 0) and (1 0 0) planes

CaF2 crystal generally has a fluorite-type crystal structure, in which the cleavage plane is {111} and the slip system is {100} 〈110〉. The mechanical properties of different crystal planes are obviously different. In this investigation, 248 nm KrF excimer laser damage experiments were carried out on three different crystal planes (100), (110) and (111) of CaF2 crystals. The laser induced damage threshold was obtained, and the relationship between crystal plane and damage characteristics was analyzed. Our work highlights were that by analyzing the relationship among crystal plane, cleavage plane and slip plane, the formation mechanism of surface morphology of (111), (110) and (100) crystal planes were summarized.

Damage technology of carbon fiber composites by high-power laser

Based on the layer characteristics of the carbon fiber and resin composites, the damage mechanism of high power laser beam on the carbon fiber target are investigated. Analyzing the laser ablation target, the layer ablation mechanism is introduced, which is composed of an ablation layer, a pyrolysis layer and an original layer. The finite element model of the laser ablation the carbon fiber composites was established, in which a Gaussian laser beam irradiated perpendicularly on the target. Because of the advantages of finite element gridding in spatial domain and finite difference gridding in time domain, the “birth and death element” method was used to accurately simulate the temperature distribution field of the laser damage target, and those elements were sequentially stripped, i.e. “killed”, exceeding the vaporization temperature “point” of the carbon fiber composites during the laser heating until the laser is shut off. Moreover, the laser damage experiment on the carbon fiber composites was carried out, the temperature distribution field of the laser irradiated target was measured, and the burn-through time of the carbon fiber target was recorded. It is found show that the birth and death element method with the sequent stripping way can be used accurately to simulate the three-dimensional temperature distribution field of the target and evaluate the laser damage efficiency to the targets.

Simulation of the nanosecond-pulse laser damage of KDP surface by the smoothed particle hydrodynamics method.

We present a simulation method to reproduce the damage crater formation and particle ejection phenomena observed in the laser-induced surface damage process of potassium dihydrogen phosphate (KDP) crystals. Based on the smoothed particle hydrodynamics method, which is commonly used for solving shock and blast problems, equivalent explosion simulation models of the laser-induced damage process have been established. Moreover, laser damage experiments combined with time-resolved techniques are performed on KDP surfaces to investigate the impact of laser fluences on the shockwave propagation and the particle ejection speed. We find that the simulation models can predict the laser-induced damage behaviors of the KDP crystal, which verifies the validity of the proposed method.

Investigation of the laser-induced surface damage of KDP crystal by explosion simulation.

Under nanosecond pulse irradiation, laser-induced damage of Potassium Dihydrogen Phosphate (KDP) crystal is a multi-physical coupling process which mainly includes energy absorption by precursor defects, temperature and pressure rise in the absorption center, and subsequent micro-explosion event. Till now, related research work mainly focuses on modeling the energy absorption stage and determining the temperature or pressure in the absorption center, but knowledge about the explosion stage is rather limited. In this paper, laser-induced damage of KDP crystal has been investigated through explosion simulation. According to the laser damage test results and morphologies of the damage craters, typical precursor defects inducing KDP surface damage have been determined. Based on the knowledge, equivalent explosion simulation models of the laser damage process have been established to reproduce damage crater formation and shockwave propagation. Finally, laser damage experiments, combined with time resolved techniques, have been utilized to investigate the variation of damage crater size and shockwave speed with laser fluences. Simulation results given by single core explosion models agree well with the experimental results at fluences lower than 60 J/cm2, while a multicore explosion model is needed to reliably simulate damage crater formation at higher fluences.

Study on the Method of Evaluating the Interference Effect of Laser on CCD Detector Based On Image

Along with laser countermeasure technology is widely used in the field of photoelectric detector, how the interference and damage degree of laser to detector, when the damage threshold is reached and how to make objective evaluation is a very concern of the people. And therefore, it has important significance to carry out the laser interference and damage experiment of photoelectric detector and propose an objective and reasonable evaluation of Ajamming effect. Combined with typical image evaluation methods such as structural similarity, correlation measurement, feature point analysis and cross entropy, this paper systematically studies the interference effect evaluation technology of laser interfered CCD detector, and finally summarizes the development trend of the interference effect evaluation technology of laser interfered CCD detector.

Effect of non-linear amplification of phase and amplitude modulations on laser-induced damage of thick fused silica optics with large beams at 351 nm

Nonlinear propagation of high power, large aperture laser beams leads to the amplification of the spatial pre-existing small scale modulations, and therefore locally increases the laser energy density as the beam propagates through the optical component. The measurement of the energy density distribution on the exit face of the tested component is therefore more challenging, as the impact of the propagation must be taken into account. It is for this reason that the damage densities of thick fused silica components have never been precisely measured. To this end, a dedicated imaging setup has been developed to accurately measure the energy density distribution on the exit face of 34-mm thick fused silica optical components during laser damage experiments with a centimeter-scale laser beam. The impact of nonlinear propagation on the beam spatial profile has been studied experimentally and confronted to numerical simulations that solve the nonlinear Schrödinger equation for the experimental spatial and phase profiles. The results clearly indicate that the imaging setup can accurately measure the amplification of the beam spatial modulations. The beam energy density on the exit face is therefore correctly measured and, for the first time, the damage density of thick optics can be accurately determined.

Using a cover layer to improve the damage resistance of gold-coated gratings induced by a picosecond pulsed laser

The chirped pulse amplification (CPA) technology is the main approach to achieve high-intensity short-pulse laser. Diffraction gratings are good candidates for stretching and compressing laser pulses in CPA. In this paper, a kind of gold-coated grating has been prepared and its laser damage experiment has been performed. The results reflect that the gratings laser damage was dominated by thermal ablation due to gold films or inclusions absorption and involved the deformation or eruption of the gold film. Based on these damage phenomena, a method of using a cover layer to prevent gold films from deforming and erupting has been adopted to improve the gold-coated gratings laser damage threshold. Since the addition of a cover layer changes the gratings diffraction efficiency, the gratings structure has been re-optimized. Furthermore, according to the calculated thermal stress distributions in gratings with optimized structures, the cover layer was demonstrated to be helpful for improving the gratings laser damage resistance if it is thick enough.

Femtosecond laser induced damage of pulse compression gratings

Laser induced damage of Au-coated gratings (ACG) and metal multilayer dielectric gratings (MMDG) for pulse compression were measured using 800±35nm femto-laser with pulse width of 30.2fs. The -1st order diffraction efficiency of the ACG is over 90% in wavelength range from 700 to 1000nm. The MMDG has a 148nm bandwidth (750–897nm) with -1st order diffraction efficiency greater than 90%. The laser damage experiment on grating samples was performed in air for single-shot damage. The single-shot damage threshold of the ACG and MMDG was determined to be 0.32±0.02J/cm2 and 0.31±0.02J/cm2, respectively. The damage morphologies of the ACG revealed that the damage was attributed to the pinholes at the base of the grating pillars and theweak adhesion between metal layer and photoresist gratings layer. The damage feature combined with near field distribution of MMDG indicated that the damage was due to the nonlinear ionization process of the valence electrons in HfO2 film. According to analysis results, the laser damage resistance of the ACG can be enhanced through avoiding the appearance of pinholes and increasing adhesion between metal layer and photoresist layer. And for the MMDG, good performance of HfO2 film, low near field enhancement and single HfO2 grating structures may increase its laser damage resistance.

Varied laser induced damage phenomena of gold coated gratings for pulse compression

In this paper, gold-coated gratings for pulse compression have been prepared and their laser damage experiments have been performed. Varied laser damage morphologies have been observed: when a 60fs-pulsed laser with energy density slightly higher than the damage threshold was used, damage morphology with a characteristic of discrete distribution of small pits was appeared. These damage pits are linearly distributed at the junction of ridges and grooves. If the laser energy density is much higher than the damage threshold, the gold films was overall ablated and the grating structure disappeared. Besides, if the gold film has poor adhesion, it was peeled off. When a 450ps-pulsed laser with energy density slightly higher than the damage threshold was used, part of grating ridges will be ablated and an obvious line exists between the ablated area and the unchanged area. In theory, the laser induced temperature field and stress field in gold-coated gratings were calculated based on the electromagnetic field using the finite element method. It is demonstrated that the temperature and thermal stress distribution characteristics are affected by the laser heating rate and the heat diffusion time (the calculated diffusion time ranges from 6fs to 450ps), which determines the laser damage characteristics. The possible damage drivers have electron hydrodynamic pressure, thermal ablation and thermal stress.

Optical and electrical properties of indium tin oxide films near their laser damage threshold

In this study, we investigated whether the optical and electrical properties of indium tin oxide (ITO) films are degraded under laser irradiation below their laser ablation threshold. While performing multi-pulse laser damage experiments on a single ITO film (4.7 ns, 1064 nm, 10 Hz), we examined the optical and electrical properties in situ. A decrease in reflectance was observed prior to laser damage initiation. However, under sub-damage threshold irradiation, conductivity and reflectance of the film were maintained without measurable degradation. This indicates that ITO films in optoelectronic devices may be operated below their lifetime laser damage threshold without noticeable performance degradation.

Correlation between laser-induced damage densities of fused silica and average incubation fluences at 1064 nm in the nanosecond regime

The chronology of the physical processes involved in the nanosecond laser damage of fused silica is investigated at 1064 nm. From experiments realized with multiple longitudinal mode pulses, the correspondence between ring pattern damage morphology and the corresponding intensity profile allows the distinction of two damage phases: an incubation phase followed by a damage expansion phase that leads to the final damage diameter. It allows us to determine both the incubation and the expansion fluences. These results are compared to damage density measurements for different laser configurations, different optics, and different environments. It was found that damage densities were as high as incubation fluences were low. This approach shows a deterministic part of laser damage in nanosecond regime and contributes to reinforce the statistical results by reducing their random nature and is more able to guide the physical interpretations of laser damage experiments.

Research on laser-induced damage resistance of fused silica optics by the fluid jet polishing method.

Laser-induced damage threshold (LIDT) is one important evaluation index for optical glasses applied in large laser instruments which are exposed to high light irradiation flux. As a new kind of precise polishing technology, fluid jet polishing (FJP) has been widely used in generating planar, spherical, and aspherical optics with high-accuracy surfaces. Laser damage resistances of fused silica optics by the FJP process are studied in this paper. Fused silica samples with various FJP parameters are prepared, and laser damage experiments are performed with 351 nm wavelength and a 5.5 ns pulse width laser. Experimental results demonstrate that the LIDT of the samples treated with FJP processes did not increase, compared to their original state. The surface quality of the samples is one factor for the decrease of LIDT. For ceria solution polished samples, the cerium element remaining is another factor of the lower LIDT.

Handling beam propagation in air for nearly 10-fs laser damage experiments

We present the design and operation in air of a laser test-bench able to measure the laser-induced damage threshold of optical materials and components with ultrashort pulses down to nearly 10fs pulse duration. Working in air environment brings the advantage of convenience and rapid diagnostics, provided that the laser beam is properly handled. As a preliminary step, a careful analysis of the spatial, spectral and temporal properties of the ultrashort laser beam is performed to characterize its propagation till the focal plane where the target is located. The results allow us to determine an upper limit of the incident energy below which the beam propagation is not affected by nonlinear effects, like Kerr effect or air ionization, which could skew the determination of laser-induced damage threshold. Finally, we demonstrate the capability of the laser test-bench by measuring the damage threshold of fused silica irradiated by single ultrashort pulses of nearly 10fs pulse duration.

Generic incubation law for laser damage and ablation thresholds

In multi-pulse laser damage and ablation experiments, the laser-induced damage threshold (LIDT) usually changes with the number of pulses in the train, a phenomenon known as incubation. We introduce a general incubation model based on two physical mechanisms—pulse induced change of (i) absorption and (ii) critical energy that must be deposited to cause ablation. The model is applicable to a broad class of materials and we apply it to fit data for dielectrics and metals. It also explains observed changes of the LIDT as a function of the laser repetition rate. We discuss under which conditions the crater-size method to determine LIDTs can be applied in multi-pulse experiments.

Nanosecond UV laser-induced fatigue effects in the bulk of synthetic fused silica: a multi-parameter study.

Multiple-pulse S-on-1 laser damage experiments were carried out in the bulk of synthetic fused silica at 355 nm and 266 nm. Two beam sizes were used for each wavelength and the pulse duration was 8 ns. The results showed a fatigue effect that is due to cumulative material modifications. The modifications have a long lifetime and the fatigue dynamics are independent of the used beam sizes but differ for the two wavelengths. Based on the fact that, in the context of material-modification induced damage, the damage thresholds for smaller beams are higher than for larger beams, we discuss possible mechanisms of damage initiation.

Fiber laser heating and penetration of aluminum in shear flow

Laser damage experiments were performed on painted and unpainted aluminum coupons using a 1.07-μm fiber laser at irradiances ranging from 0.2 to 1.4 kW/cm2 in a wind tunnel operating at Mach 0.1 to 0.9. Coupon penetration times of ∼0.5 to 10 s were measured using a silicon photodiode viewing a Lambertian scatter plate placed behind the target. Despite the thin, 0.81 to 0.95 mm, samples and large laser spot diameters, 2 to 3 cm, the effects of radial heat conduction dominate for irradiances of <1 kW/cm2. The fluence required to melt the back surface scales linearly with paint absorbance and the effects of paint aging have been observed. Penetration times for gray-painted aluminum at 287 W/cm2 decrease by 45% as the airflow speed increases from M=0.1 to M=0.2, but remains constant for flow speeds up to M=0.7.