Carbon fiber composite has been widely used in structural engineering applications, and research on the mechanical properties under various conditions is attractive. The study experimentally investigated the damage effect of CW laser ( λ=1064nm ) on carbon fiber composite strip under preloading. The effects of laser power and preloading on fracture morphology, temperature of the center of the irradiation area and fracture time were investigated. The experimental results show that when the preloading was lower than the fracture threshold, the laser irradiating could cause matrix damaging, fracturing with fluffy wire drawing and burning through for laser power density of 236.17W/cm2, 407.39W/cm2, 634.39W/cm2, respectively. The maximum temperature of the spot center increased with the increase of laser power, with rising and falling edges varying in a stepwise way. Under the laser irradiation with the same power density, the higher value of preloading corresponded to the less fracture time. However, when the preloading was 20% over the fracture threshold, the influence of the laser power density was significantly reduced. Similarly, when the laser power density was 634.39W/cm2, the fracture time was less influenced by the value of
To study the influence of laser intensity and temperature on the performance of laser power converters (LPCs), a two-dimensional model of an In0.3Ga0.7As LPC by the finite element method was established. The validity of the model was verified by comparing the theoretical value with the experimental results. The factors that influence the performance of LPCs were analyzed from the perspective of recombination. Results indicate that the existence of grids at the front surface improves the collection of carriers efficiently, and the influence of temperature and laser intensity on carriers recombination is quite different at 0 and Vm (voltage at maximum power point) bias voltages. The research of this paper provides a reference for the optimization of LPCs.
A microphone was used to study the characteristics of acoustic emission for millisecond laser-induced damage of BK7 glass. Different temporal and spectral distributions were obtained for the front and rear surface damage processes. The front surface damage was associated with the strong thermal melting process, and the size of the conical molten pit was strongly linked to the intense oscillating period of the acoustic signal. The effects of the detection distance and angle on the spectrum below 5 kHz, which were induced during the front surface damage process, were found to be associated with the distribution of the ejection expelled out of the molten pit. The results indicate that the detection of acoustic emission can be used as a real-time online method to obtain information on the millisecond laser-induced damage.
In this paper, a millisecond laser combined with a nanosecond laser (CPL) was used to interact with the BK7 glass. The influence of the laser fluence and the delay time on the rear surface damage feature was studied. Results show that the damage on the rear surface of BK7 glass was generated by the stress due to the CPL irradiation. Two types of damage morphologies called small damage points (SDP, on the order of hundreds of micrometers) and large damage points (LDP, on the order of several millimeters to centimeters), respectively, were observed. The SDP can be generated by the CPL with low millisecond laser fluence or high delay time, while the LDP showed the opposite feature. The averaged size of the damage point increased with the millisecond laser fluence and dropped rapidly when the delay increased from 600 μs to 800 μs.
A 2D numerical model is developed to investigate the transient dynamics of molten pool and thus the bur formation mechanism in millisecond pulsed laser drilling process. The model features the utilization of the sharp interface method for accurate consideration of the complex boundary conditions on the hole wall and a comprehensive hydrodynamic calculation for both the gaseous and liquid phases. The model gives good prediction of the bur phenomena, and more importantly, provides detailed information regarding the multi-phase interaction and its effects on hole dynamics, also on the bur formation. It is shown that different substrate can cause different coupling effects between the vapor plume and molten pool and hence produce holes of different shapes. The model gives a basic study of the bur formation during the ablation process of different metals and shows a virtual technique for the visual of the movement of melt and vapor. And the obtained results show good qualitative correspondence with experimental data.
Water clouds are considered as the common dispersion systems suspending in the air. In general, droplets can be treated as a transparent dielectric for the laser field. However, once the intensity of laser exceeds the breakdown threshold, laserinduced plasma will be generated in the droplet. This plasma is able to significant influence the propagation of laser field. Since the water clouds are constituted by the countless droplets, it is reasonable to study the interaction between intense laser field and a single droplet as the starting point. The laser-induced plasma is usually generated instantaneously in a micro spatial volume. It is difficult to reveal the detail structure of plasma. We will provide a transient coupling model to study the time-evolution of the laser-induced plasma propagating in a single droplet. Using the above model, we will bring insight into the breakdown threshold firstly. On the other hand, there are abundant features in the both plasma and its coupling laser field. The plasma is initially generated at the location where laser field propagates away from the droplet, if the intensity of the laser is not very high. Meanwhile, after the plasma generates, the droplet becomes opaque. Large amount of laser energy then is deposited in the droplet. The saturation of the energy deposit can be revealed in our model. We would expect this transient coupling model is helpful to estimate the propagation length of the intense laser pulse while it is passing through the water cloud.
The temperature rise of the InGaAs solar cells which under the continuous laser exposure is theoretically calculated, and experimentation,correspondingly designed to bismuth telluride thermoelectric power generation and cooling system,thereby enhancing the overall photovoltaic system integrated photoelectric conversion efficiency.
The potential applications of laser-induced bubbles are gradually revealed. And the performance of multiple - bubbles also attracted considerable attention. This paper is intended to study the complex interaction among three in-line arranged in-phase bubbles. This work illustrates the interactions of three bubbles oscillation and the shockwave motion after the recombination of the plasma nanosecond laser excited. The Volume of Fluid (VOF) model is used to numerically analyze the behaviour of same equilibrium size, same distance and in-phase multiple-bubbles, which enables tracking of the gas-liquid interface and the field. The numerical results indicate that, in the expanding stage, due to the pressure gradient, bubbles at both ends move towards the centre, while the bubble surfaces facing to other bubbles get flattening. The central bubble has longer oscillation period than the side bubbles. In the shrinking stage, the side bubbles get deformation faster, and then collapse with a jet or get adhere to the central bubble. The initial high-pressure bubble radiates a shockwave at the beginning of the expansion. The shock wave propagates outwards from the point source in a circular pattern, resulting in interference in the overlap of the two shock waves. A curved pressure wave, which is parallel to the in-line array, is produced by the interference of multiple shock waves. The pressure wave decays to an acoustic wave after a certain distance according to its initial intensity. In particular, a significant variable γ=D/(R+R) deserves studying in this progress.
Laser-induced periodic surface structure (LIPSS) is a universal phenomenon which occurs for both continuous laser and pulsed laser. Recently, most studies are focus on LIPSS irradiated by fs laser. However, LIPSS irradiated by continuous laser still need to be carefully studied. Here, We study LIPSS in silicon wafer irradiated by continuous laser for different duration time and power. For the same power, we can observe the evolution process of LIPSS for different time. It is surprising that the evolution process of LIPSS seems to be layered, which occurs for different power. The inner layer occurs at first, then the outer layer occurs. Our study can be used to control the formation of LIPSS.
In the laser wireless power transmission (LWPT) system, the solar panel plays a decisive role as the receiving end of the energy. As the transmission medium of energy in LWPT system, the energy of laser presents generally Gauss distribution, resulting in uneven energy of the laser received by the solar panel, which may affect the transmission efficiency and capacity of the system. In this paper, a 1070nm continuous fiber laser is used to irradiate the In0.3Ga0.7As solar panel, and the temperature distribution on the back of the panel and the IV characteristics were recorded. The results showed that the temperature distribution on the back side of the solar panel was almost the same under the conditions of the same laser power but different energy distribution. In terms of performance of the panel, due to the increase in beam uniformity, the short-circuit current increased by 33.4%, the maximum output power increased by 18.5%. In addition, the irradiation of different laser power was also studied in this paper. The influence of different laser intensity and different beam uniformity on the efficiency of the panel were given.
Non-uniform temperature field in optical transparent glasses induced by high power Gaussian laser irradiation would introduce temperature gradient which will cause thermal lens effects inside materials. Such thermal lens influences on long pulse laser processing are usually omitted in previous studies. However, thermally-induced refractive index change in situ could have a relatively large impact on subsequent incident laser especially under the action of high power laser. In order to obtain a quantitatively transient results of thermal lens effects caused by long pulse laser, we carried out numerical simulations of temperature rise, refractive index change and their influences on light trail in K9 glass heated by a millisecond pulse laser. Different laser energy and glass thickness were applied to reveal the dependence of thermal lens and laser and glass parameters. Results show that the thermal lens effects would increase refractive index in K9 glass and reconverge subsequent laser beam consequently whose amplitude is proportional to incident laser power and glass thickness. The simulation results are compared with the previous experimental results and are consistent in magnitude of refractive index change. But there is a certain gap in refractive index field distribution in the direction of laser radius due to the neglect of influence of refractive index raise to susequent lasers in temperature simulations. This work would provide a reference in the field of millisecond pulse laser processing optical transparent materials.
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