A real-time method based on laser scattering technology was used to detect the interaction process of GaAs with a 1080 nm laser. The detector collected the scattered laser beam from the GaAs wafer. The main scattering sources were back surface at first, later turn into front surface and vapor, so scattering signal contained much information of the interaction process. The surface morphologies of GaAs with different irradiation times were observed using an optical microscope to confirm occurrence of various phenomena. The proposed method is shown to be effective for the real-time detection of GaAs. By choosing a proper wavelength, the scattering technology can be promoted in detection of thicker GaAs wafer or other materials.
To investigate the heat accumulation effect of the laser pulse train, a two dimensional finite element calculation model is established to calculate the temperature field of Aluminum target based on the Fourier heat transfer theory. Take account of the influence of the repetition rate of laser, four different repetition rates (5 kHz, 10 kHz, 50 kHz and 1 MHz) pulse laser train and continuous wave (CW) laser are analyzed in this study. The results indicate that under the same average power and irradiation time, the peak temperature and accumulative temperature increase with the decrease of the repetition rate. With the increase of the repetition rate, the heat accumulation effect is more closer to the CW laser. The heat accumulation effect of pulse laser train with lower repetitive rate is better.
Thermomechanical behaviour of a glass/epoxy composite plate under local laser irradiation is investigated. Physico-chemical transformations and gas transport in a matrix and fibers are describe by Arrhenius and Darcy's law. The changes of material thermal properties are expressed in terms of the volume fractions of fiber, resin, gas and char. At the same time, we take into account the effects of pore pressure and elevating temperature on thermal stresses and strains. It is established that transverse stress, radius stress and interlayer shear caused by local heating and pore pressure are causes of delamination and cracking of composite plates under laser heating. And interlayer shear can lead failure of composite fast.
A 3D numerical model has been built to investigate anisotropic thermal stresses of (110) silicon induced by millisecond laser. The 12 slip systems resolved shear stress field of the silicon was obtained by using the FEM. The excess resolved shear stress field is identified. comparing to the experiment of the millisecond irradiating (110) PIN photodiode, we conclude that the thermal slips are introduced duo to the anisotropic thermal stresses of silicon surpassed the critical yield stress and brittle cracks are introduced due to the initiation points offered by the thermal slips which will reduce the fracture strength greatly. These thermal slips and brittle cracks increase the dark current of the photodiode greatly.
The interaction of CW fiber laser and monocrystal silicon <100> is investigated experimentally and numerically. In the experiment, the damage morphologies are detected by a CCD and an optical microscope. The damaged silicon appears an evident molten pool within the laser spot and several cracks on the surface and slip damage, which indicate that the damage mechanism includes melting and thermal stress damage. The damage morphologies show two types of cracks including radial crack and circumferential crack. Otherwise, an obvious central hillock is found in the molten pool, which may be produced by the fluctuation of the thermal-stress filed and resolidification of the central molten silicon after irradiation. In the numerical simulation, a two-dimensional axisymmetric physical model is established based on the thermo elastic-plastic and classical heat transfer theory and Von Mises yield criterion. The simulation results indicate that the temperature and the stress in the irradiation center are always the highest on the specific condition, which may contribute to the occurrence of the central hillock. The gradient of hoop stress is bigger than the radial stress, thus, it can be inferred that the appearances of the radial cracks in the experiment were closely related to the hoop stress.
The photoelectric parameters degradation of Si-based PIN photodiodes irradiated by 1064 nm millisecond Nd:YAG laser has been measured. The samples were the commercial silicon PIN photodiodes BPW34 with plastic package. The applied laser fluence levels range from 20J/cm2 to 1400J/cm2. Surface damage morphology, dark current and sensitivity were investigated for the irradiated photodiodes. It has been shown that the dark current was the first and the most sensitive degradation parameter, and we believe that the dislocation introduced by the tangential component of thermal stress in the  and  direction was the main reason. The sensitivity decrease until the dark current reach to μA magnitude and the surface have melted seriously, the finite element method was used to calculation the dopant redistribution process. It shows that the degradation of sensitivity depends greatly on the process under various applied laser fluencies.