- 标题
- 摘要
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- 实验方案
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Theoretical Investigation of Thermal Effects in High Power Er <sup>3+</sup> /Yb <sup>3+</sup> - Codoped Double-Clad Fiber Amplifiers for Space Applications
摘要： In this paper, a multiphysics numerical model based on the spatial-dependent rate equations and 3-D non-homogeneous heat conduction model is used to investigate the performance of Er3t/Yb3t-codoped double-clad fiber amplifiers with respect to the constraints associated with space applications. The effects of fiber length, coating thickness, and core radius changes are analyzed. Furthermore, the impact of thermal heating due to the high power optical signals propagating along the fiber on the amplifier gain is examined. The temperature dependence of the refractive index, emission and absorption cross sections, as well as the radiation induced attenuation is derived and modeled. It is observed that the coating thickness affects the temperature distribution along the whole fiber length. Thicker coating mitigates the temperature variation along the fiber as well as it improves the temperature difference between the core center and the outer fiber surface. Moreover, larger core results in higher optical gain and shorter fibers. By numerical results, it is inferred that the thermal effects could strongly degrade the whole amplifier performance.
关键词： heat conduction,rare earth,fiber amplifier,thermal analysis
更新于2025-09-23 15:23:52
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New approaches on laser micro welding of copper by using a laser beam source with a wavelength of 450 nm
摘要： Laser micro welding is specified with welding geometries below 1 mm and is used with increasing demand for contacting electronic components such as battery and fuel cells. Fiber lasers with a wavelength in the near infrared range (IR, λ ≈ 1 μm) have established themselves for this purpose. The laser welding process allows processing of parts in the micron range but reduces the surface quality of the processed parts at the same time. Furthermore, weld defects can occur due to process instabilities caused by the low absorptivity (<5%) of copper for infrared radiation. Therefore, alternative laser beam sources and processes have to be established, to avoid these negative effects on the weld seam quality. Laser beam sources in the visible wavelength range (VIS) prove to be an alternative due to an increased absorption of the laser energy in copper-based alloys. This paper presents the observation of laser micro welding of Cu-ETP and CuSn6 specimen with a thickness between 150 μm and 1 mm. The diode laser is specified by a wavelength of 450 nm and a nominal output power of 150 W. The surface roughness of the weld seam and the overall weld seam geometry for heat conduction welding are investigated. The laser energy absorption is measured using two integrating spheres to compare the results quantitatively to measurements conducted with laser sources of 1070 nm and 515 nm. For detailed observation high speed imaging is used to observe the melt pool dynamics. Simulations are conducted, to optimize the dimensioning of optics and laser beam source. Finally, the possible use of the novel laser beam source for various technical joining applications is discussed and evaluated and the influence of the use of protective gas is observed.
关键词： heat conduction welding,scanner system,laser micro welding,copper,modelling,450 nm
更新于2025-09-23 15:21:01
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Process studies on copper laser beam welding over gap by using disc laser at green wavelength
摘要： The increasing demand for the substitution of the internal combustion engine vehicles to the battery electric vehicles requires beside battery cells high performance power electronic devices such as power control units (PCU). However, a combined requirement of high junction temperature stability and a large joint area of the interconnection on the PCU is a challenge for the conventional joining method such as soldering and wire bonding process. The Laser Impulse Metal Bonding (LIMBO) process enables a high temperature stable weld joint and large joint area. During the LIMBO process only minimized thermal stress is induced into the underlying substrate by a spatial separation between both joining partners in an overlap configuration with a gap. Hence, an energetic separation between the melting and joining phase is given. In this paper, the LIMBO process is firstly investigated with the disc laser at wavelength λ = 515 nm. Due to the enhanced absorptivity of the laser beam at this wavelength on copper material, the process duration of the LIMBO process is about the half compared to the LIMBO process with wavelength λ = 1064 nm.
关键词： Shadow projection,Green laser beam,Heat conduction welding mode,Laser beam micro joining,LIMBO
更新于2025-09-23 15:19:57
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Twoa??dimensional model of heat flow in edgea??emitting laser revisited: A new and more versatile approach
摘要： An analytical, two-dimensional, stationary model of heat flow in edge-emitting laser is revisited. In the work, we show how to use this approach to be able to calculate the temperature of the entire device including the most susceptible for thermal runaway region, namely the vicinity of the joint of mirrors and an active layer. Numerical tools based on our considerations are implemented in Matlab code and available at the software developer's web site. A procedure of investigation of surface recombination at facets with the help of our model combined with mirror temperature measurements is proposed. To get an insight in reasonableness of our theoretical research, we calculated temperature profiles and surface recombination velocities for example devices and successfully confronted them with results found in the literature.
关键词： temperature distribution,catastrophic optical damage,edge-emitting laser,heat conduction equation,thermal analysis,mirror temperature
更新于2025-09-23 15:19:57
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Transient thermoelastic response in a cracked strip of functionally graded materials via generalized fractional heat conduction
摘要： This work is devoted to analyzing a thermal shock problem of an elastic strip made of functionally graded materials containing a crack parallel to the free surface based on a generalized fractional heat conduction theory. The embedded crack is assumed to be insulated. The Fourier transform and the Laplace transform are employed to solve a mixed initial-boundary value problem associated with a time-fractional partial differential equation. Temperature and thermal stresses in the Laplace transform domain are evaluated by solving a system of singular integral equations. Numerical results of the thermoelastic fields in the time domain are given by applying a numerical inversion of the Laplace transform. The temperature jump between the upper and lower crack faces and the thermal stress intensity factors at the crack tips are illustrated graphically, and phase lags of heat flux, fractional orders, and gradient index play different roles in controlling heat transfer process. A comparison of the temperature jump and thermal stress intensity factors between the non-Fourier model and classical Fourier model is made. Numerical results show that wave-like behavior and memory effects are two significant features of the fractional Cattaneo heat conduction, which does not occur for the classical Fourier heat conduction.
关键词： functionally graded materials,thermal stress,crack,time-fractional heat conduction,phase lag of heat flux
更新于2025-09-19 17:15:36
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Study on the maximum electric power supplied to copper bromide vapor lasers
摘要： Copper and copper-compound vapor lasers are most powerful in the visible spectrum with output power over 100 W. They offer unique properties including a laser beam with high coherence and convergence and high average output powers with relatively small dimensions. Recently, these lasers, and in particular the copper bromide (CuBr) laser, have been widely used as radiation sources and vapor brightness amplifiers in a new type of laser active optical systems, designed for the visual monitoring and control of fast processes shielded by intense background lighting. However, new problems arise with the development of such optical systems, related to the laser technology and the optimization of their operating parameters. Important operating characteristics of copper lasers include the input electric power and the gas temperature of the discharge. The upper limit of the laser power that can be supplied to the gas discharge is studied herein by considering the permissible thermal population thresholds of the lower level of the λ = 510.6 nm laser line. The application of enhanced analytical models based on a steady-state heat conduction equation and computer simulations enables the development of a methodology to determine the maximum possible electric power that can be supplied to the gas discharge, taking into account its radial distribution across the tube cross-section. This methodology is then applied to the case of an actual small-bore CuBr laser used as a brightness amplifier.
关键词： Copper vapor laser,Gas temperature,Copper bromide (CuBr) laser,Computer simulation,Laser active optical system,Heat conduction
更新于2025-09-19 17:13:59
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Modelling the heating process of CFRP by cw-laser radiation with special focus on the heat transfer by thermal radiation between the carbon fibers
摘要： In our talk, we present results of numerical calculations that describe the thermal development within a laser-impacted laminate structure made of carbon layers embedded in a polymer matrix. The FEM-calculations show, that a significant part of the heat transfer is caused by radiative heat transfer between the carbon layers at elevated temperatures. In addition to the FEM calculations, we derive analytical relationships that allow the calculation of equivalent material parameters, especially an equivalent temperature-dependent, anisotropic thermal conduction coefficient. Thus, larger structures in the mm- and cm-range consisting of multiple carbon layers can be described by a simpler geometry of a homogenous material without the need to consider the individual carbon layers having a diameter of a few μm.
关键词： heat conduction,equivalent thermal conduction coefficient,inter fiber thermal radiation,CFRP composite,FEM-calculations
更新于2025-09-12 10:27:22
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Temperature distribution during laser based heat conduction welding of CFRP
摘要： For the implementation of carbon fiber reinforced (CFRP) parts, these need to be assembled to more complex structures. Therefore, laser transmission welding was transferred to heat conduction welding for joining thermoplastic CFRP to itself. The goal of these investigations was to determine the influence of the focal point geometry and the main fiber orientation within the CFRP on the temperature distribution at the upper joining member. A set-up was chosen consisting of two thermo cameras in order to measure the process temperatures on top and underneath the upper joining member. Furthermore, the heat affected width was determined and correlated to the process temperatures.
关键词： seam strength,carbon fiber,thermoplastic,contour welding,process temperture,heat conduction welding
更新于2025-09-12 10:27:22
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Laser welding of copper using a high power disc laser at green wavelength
摘要： The trend towards renewable energies and electromobility is increasing the demand for copper. Laser welding as a flexible and fully automatable process is being more frequently employed to join copper materials. The use of green laser radiation compared to infrared laser radiation has the advantage of a significantly higher absorption coefficient for copper materials. Therefore, high power laser sources emitting at a green wavelength promise a more stable and a more efficient process. In this paper, experimental investigations with a green continuous wave laser radiation at a maximum power of 1 kW are presented. Using design of experiments, the process limits are determined depending on the laser power and the welding velocity. Furthermore, the potential of heat conduction welding using this laser source is investigated.
关键词： Green wavelength,Laser material processing,Heat conduction welding,Process limit,Copper
更新于2025-09-12 10:27:22
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Parabolic two-step model and accurate numerical scheme for nanoscale heat conduction induced by ultrashort-pulsed laser heating
摘要： Simulation of nanoscale heat transfer phenomena has attracted great attention, particularly the nano-scale heat conduction induced by ultrashort-pulsed laser heating. In this article, we propose a nanoscale parabolic two-step model and an accurate numerical scheme for thermal analysis of the nanoscale heat conduction induced by ultrashort-pulsed laser heating. To this end, we first introduce the Knudsen number (Kn) into the original parabolic two-step heat conduction equations and couple them with the Kn-dependent and temperature-jump boundary condition. We then develop a fourth-order accurate compact finite difference method for solving the nanoscale model. Stability and convergence of the obtained numerical scheme are analyzed theoretically. We finally test the accuracy and applicability of the nanoscale model and the obtained numerical scheme in three examples. By choosing various values of the Kn and the parameter α in the boundary condition, the simulation could be a tool for analyzing the nanoscale heat conduction induced by ultrashort-pulsed laser heating.
关键词： Nanoscale heat conduction,Convergence,Compact finite difference scheme,Stability,Ultrashort-pulsed laser heating
更新于2025-09-12 10:27:22