Most methods to research thermal effect are based on the analytical method, but he calculation processing is too complex, and we can get analytical solution only in a very small number of simple cases. We research the issue by use of finite element method (FEM). In this paper, the main research areas are as follows: The first, a theoretical mode of pulse laser leading to thermal stress damage of dielectric material is developed. Based on this theoretical model, transient distributions of temperature field and thermal stress field are analyzed by finite element method (FEM). The FEM method involves element discretion, element analysis, and overall analysis. Transient temperature field and stress field are simulated by using FEM software. Numerical results indicate: There is large temperature gradient in radial directions, while small temperature gradient exists in axis directions, and central temperature will be higher as power density of laser is higher. The results demonstrate that thermal stress damage is critical and circumferential stress play a main role in damage mechanism, the principle and methods of film measurement are summarized, the results in this paper may provide theoretical base for further research.
In order to improve the capacity of beam collimation for laser beam expander, it is necessary to design a more reasonable
and feasible structure of beam expander system. Laser beam expander is used to compress the laser divergence angle, in
order to reduce the energy losing in long distance scanning acquisition system. This paper introduces the working
principle and design idea of the laser beam expander, the collimating multiplying power focal length and the collimated
magnification formula of expander main, secondary mirror. According to the third-order aberration theory, Considering
the spherical aberration, sine difference and divergence angle, the reasonable analysis of optical path, ZEMAX optical
design software was used to design large-diameter laser beam expander and analysis and optimize, And given the actual
design data and results. Display the maximum optical path difference is ±0.01λ of the main light ray and each light ray.
To combination the rear- group objective lens of Galileo and Kepler beam expander, a large-diameter(1.475m) laser
beam expander was designed with 0.2m in the diameter, 1/2m in the relative caliber. In the objective lens System, a
high-order aspherical was used to the aberration of extra-axial point. we can see that the image quality is close to the
diffraction limit from the curves of wavefront. In addition to improve image quality effectively, the system has the
characteristics of simple structure, less costly and less design difficulty to compare with the other beam expanding
system. And make the output beam's divergence angle smaller, energy density higher, and the beam quality has been
greatly improved. The results show that the beam expander is fully meet the design requirements, the use effect is good.
Design and research of laser beam expanding system not only improves the quality of the laser beam in the laser system,
but also enlarge the application field of laser technology in photoelectric system.
In this article ,we use finite element method to simulate the process of multi-pulse laser irradiate on fused silica.
Simulation results show that:during laser pulse radiation, the temperature rise of the laser-radiating fused silica surface
center point is nearly linear. During the pulse interval without pulse acting, due to none of thermal source or energy
concentration and the fused silica being at cooling phase, the temperature of the laser-radiating fused silica surface center
point declines sharply. At the fused silica surface where r=0.6mm, hoop stress turns to be tensile stress. When the next
pulse starts to act, the stress increases rapidly once again the maximum value of it is higher than the former one. Thus,
we can judge that the laser accumulation acts a major role in increasing tensile stress effect.
Meanwhile, we can figure out that the stress increase rate generated by the pulse laser of duty ratio 1:10 is higher than
the one of duty ratio 1:20 during the whole procedure. Along with shorter intervals of every two neighbor laser pulses of
duty ratio 1:10, the regression time of the tensile stress is comparably shorter. Thus, during the whole laser radiation
procedure, the initial tensile stress of every pulse of duty ratio 1:10 is greater than the one of duty ratio 1:20. Hence we
obtain the conclusion that, it’s much easier to generate damage when the pulse numbers in unit time increase with other
parameters of the laser do not change.
In this paper, we study and establish the theoretical model of thermal stress damage of dielectric film in film/substrate
systems caused by long-pulse laser, based on which transient distributions of temperature field and thermal stress field
are simulated using the finite element method(FEM) and then analyze the mechanism of the damage. In accordance with
the basic equation of heat conduction equation and thermal stress equation, the physical model of dielectric film and the
substrate transient temperature field and thermal stress field is developed with the assumption that the dielectric film and
the substrate are isotropic and their thermal parameters do not change with temperature.
On the foundation of theoretical analysis, transient of temperature field in dielectric film in film/substrate systems under
long-pulse laser irradiation is simulated and calculated. The numerical results indicate that great temperature gradient
exists in dielectric film and substrate in radial direction but smaller one exists in axial direction. When the laser power
density is increasingly larger, the temperature gradient in radial direction is larger and the temperature in the center of the
film is higher. Transient thermal stress field in dielectric film in film/substrate systems under long-pulse laser irradiation
is simulated. Numerical results show that, the damage to the dielectric film caused by long-pulse laser is mainly due to
thermal stress damage process which circumferential stress acts a primary role in. Such damage is a final result of the
substrate being under thermal stress. For film/substrate system, the damage under long-pulse laser radiation starts from
the substrate. When the laser power density is increasingly larger, the dielectric film is more vulnerable to damage and
damage zone is greater.
The result of this paper provides theoretical foundation not only for research of theories of dielectric film and substrate
thermal stress damage and its numerical simulation under laser radiation but also for long-pulse laser technology and
widening its application scope.
With the rapid development of power industry, the number of SF6 electrical equipment are increasing, it has gradually
replaced the traditional insulating oil material as insulation and arc media in the high-voltage electrical equipment. Pure
SF6 gas has excellent insulating properties and arc characteristics; however, under the effect of the strong arc, SF6 gas
will decompose and generate toxic substances, then corroding electrical equipment, thereby affecting the insulation and
arc ability of electrical equipment. If excessive levels of impurities in the gas that will seriously affect the mechanical
properties, breaking performance and electrical performance of electrical equipment, it will cause many serious
consequences, even threaten the safe operation of the grid.
This paper main analyzes the basic properties of SF6 gas and the basic situation of decomposition in the discharge
conditions, in order to simulate the actual high-voltage electrical equipment, designed and produced a simulation device
that can simulate the decomposition of SF6 gas under a high voltage discharge, and using fourier transform infrared
spectroscopy to analyze the sample that produced by the simulation device. The result show that the main discharge
decomposition product is SO2F2 (sulfuryl fluoride), the substance can react with water and generate corrosive H2SO4(sulfuric acid) and HF (hydrogen fluoride), also found that the increase in the number with the discharge, SO2F2concentration levels are on the rise. Therefore, the material can be used as one of the main characteristic gases to
determine the SF6 electrical equipment failure, and to monitor their concentration levels.