The result shows that the thermal effect during the laser irradiation leads to the degradation of mechanical properties of Nomex honeycomb sandwich panel. High temperature rise rate in the specimen is another main reason for the shear stiffness degeneration. This research provides a reference for the degradation of mechanical properties of composite materials in laser irradiation and proposes a new method for the study of laser interaction with matter.
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The laser radiation induced thermal effects on the interactions between the tangential airflow and aluminum alloy are investigated numerically in this paper. A two dimensional model is developed for analysis of the evolutions of the temperature, stress and displacement of the flow and the aluminum alloy sheet at different flow speed through finite element method FEM.
Furthermore, in the situation of a thin aluminum alloy sheet irradiated by a large laser spot, the laser-induced thermal stress plays a leading role in the rupture of the sheet below the melting temperature. The airflow-induced shear stress and the pressure difference between the front and the rear surfaces of the sheet are minor effects compared to the thermal stress mentioned above.
In addition, the bulge of the sheet induced by the laser heating would interact with the tangential airflow and lead to the formation of the downwind vortices, which may lead to a stronger shear stress. A vortex-induced oscillation appears when the Reynolds number of the airflow changes caused by the increase of the bulge height. And this vortex-induced oscillation would contribute to the damage of the aluminum sheet. The laser-induced damage of fused silica optics significantly restricts the output ability of large laser systems.
Hydrofluoric HF -based etching is an effective processing to eliminate impurities and mitigate subsurface defects. Traditional polished fused silica samples were etched for different time in a HF-based etchant 2. The laser-induced damage thresholds LIDT were measured by R-on-1 method, and fourier transform infrared absorption spectras of the samples were obtained. The more surface materials were removed, the higher LIDT was obtained. The analysis of the infrared spectra illustrated that structural densification materials were removed during the etching, and thus the LIDT can be improved.
Time-resolved surface temperature of single crystal silicon was measured by an infrared radiation pyrometer. The silicon sample was irradiated by two pulsed Nd:YAG lasers with pulse duration of 1ms superposed by 7ns pulses, referred to as combined pulse laser CPL. The change of the damage radius with the millisecond ms laser energy density was studied, and then compared with that of single ms laser irradiation. An axisymmetric numerical model was established for calculation of the temperature field distribution while silicon was irradiated by single ms laser and CPL, respectively.
Compared with experimental results, the CPL-silicon damage mechanism was discussed. The present work reports the investigation of the thermal and mechanical behaviour of aluminium alloys under the combined action of tensile loading and laser irradiations.
The two types of aluminium alloys Al and Al are used for the experiments. The continuous wave Ytterbium fibre laser wavelength nm was employed as irradiation source, while tensile loading was provided by tensile testing machine.
The effects of various pre-loading and laser power densities on the failure time, temperature distribution and on deformation behaviour of aluminium alloys are analysed. The experimental results represents the significant reduction in failure time and temperature for higher laser powers and for high load values, which implies that preloading may contribute a significant role in the failure of the material at elevated temperature.
The reason and characterization of material failure by tensile and laser loading are explored in detail. A comparative behaviour of under tested materials is also investigated. This work suggests that, studies considering only combined loading are not enough to fully understand the mechanical behaviour of under tested materials.
For complete characterization, one must consider the effect of heating as well as loading rate. The objective of the work reported is to study experimentally on the removal of corrosion layer from the ancient coins using laser beam as the conservation tool. With the use of Q-switched Nd:YAG laser radiation at nm, dry laser cleaning, steam laser cleaning and chemical-assisted laser cleaning were used to find out a more suitable and efficient laser treatment for corrosion removal.
Cleaning tests were performed on ancient Chinese coins. Experimental results shows that the dry laser cleaning was not successful at removing all types of corrosion crust. It was possible to remove the outer thicker layer of the corrosion products typically known as patina , but failed on the thinner layer of cuprite. The steam laser cleaning could decrease the initial removal threshold and improve the removal efficiency especially for the oxidation with powdery structure.
As for chemical-assisted laser treatment, the cleaning results demonstrate that the combination of laser and chemical reagent could provide a considerable improvement in corrosion removal compared with the conventional laser treatments. Most of the corrosion contaminant was stripped, even the cuprite layer. Moreover, no secondary pollution was formed on the cleaned surface.
X-ray fluorescence was applied to determine the variation of composition of surface layer and bulk metal before and after the coins cleaned. Fused silica optics were treated by dynamic etching using buffered hydrofluoric acid BHF with different etching depths. Surface qualities of fused silica were characterized in terms of surface roughness, surface profile and photoluminescence PL spectra. The results show that dynamic etching has a slight impact on surface RMS roughness.
PL defects gradually reduces by dynamic etching, and laser damage resistance of fused silica continuously increases with etching depth extending. However, surface profile continuously deteriorates with etching depth increasing. Appropriate etching amount is very important for improving damage resistance and mitigating surface profile deteriorating of fused silica during etching process simultaneously. The study is expected to contribute to the practical application of dynamic etching for mitigating laser induced degradation of fused silica optics under UV laser irradiation. Besides the excessive saturation effect, a new mechanism of temporary black screen of CCD camera induced by laser is found.
The final output of CCD camera is the difference between the signals in effective pixels and optical black pixels. As the effective pixels of CCD camera are being irradiated by intense laser, many carriers induced by photo overflow from effective pixels into the optical black pixels. As a result, both the effective and optical black pixels will reach saturation, which makes the final output of CCD become zero. This effect has the same black screen phenomenon as the excessive saturation, and is named as pseudo-excessive saturation effect in this article.
In the paper, the performance of Si devices with change of carrier lifetime was reported with finite volume method. In the two-dimensional axisymmetric semiconductor model, based on Si p-n junction structure, direct recombination, auger recombination and the SRH Shockley-Ready-Hall recombination were taken into consideration.
Fourth International Symposium on Laser Interaction with Matter | () | Publications | Spie
Both cathode and anode was made via ohmic contact. Numerical simulation had been studied under different bias voltage and carrier lifetime. Compared with the results, it was found that the device performance was affected by the minority carrier lifetime obviously. It also inferred that performance of Si devices was degenerated by laser indirectly. Considered the pyrolysis and the internal gas convection, a three-dimensional mathematical model based on the conservation of energy, had been developed for predicting the pyrolysis behavior of composite subjected to laser.
The numerical results agree well with the experimental results on the whole.
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The results reveal that as the irradiation time continues, the thermal ablation rate begins to decrease gradually and then tends to be steady after a rapid increase. The oxidation can be effectively restrained due to a nitrogen protection. A mesoscopic method is developed to analyze the temperature field of composite materials under laser radiation based on their meso-structures.
Laser energy coupling to fibers and matrix are characterized by different absorption coefficients, and multi-phase heat transfer process in composites is solved by the lattice Boltzmann method LBM. In this paper, we demonstrate the laser simulation adequacy both by theoretical analysis and experiments. We first explain the basic theory and physical mechanisms of laser simulation of transient radiation effect of semiconductor. Based on a simplified semiconductor structure, we describe the reflection, optical absorption and transmission of laser beam.
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Considering two cases of single-photon absorption when laser intensity is relatively low and two-photon absorption with higher laser intensity, we derive the laser simulation equivalent dose rate model. Then with 2 types of BJT transistors, laser simulation experiments and gamma ray radiation experiments are conducted. We found good linear relationship between laser simulation and gammy ray which depict the reliability of laser simulation. Cai; Y.
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