Development Of The Porous Non-deformation Silicon Mirror

During the high power laser works, the beam quality will be deteriorated because of the thermal deformation of the reflector, which induced by absorption part of laser energy. At present, the active water-cooling is the most effective and widely utilized method. However, conventional water-cooled mirror is difficult to meet the requirement of high power laser. As a kind of highly efficient heat dissipation structure, the porous structure has a high surface area/volume ratio and brings additional thermal dispersion effects, the non-deformation mirror with a porous structure heat sink has a strong ability to restrain heat deformation. In addition, as an excellent reflector material, Si is widely utilized as reflector mirror material in high power laser because of its excellent thermal properties and optical machinability. However, existing3D processes technologies are hardly to fabricate the porous non-deformation Si mirror. In this thesis, a new kind of porous non-deformation Si mirror is fabricated by Selective Laser Sintering (SLS), and the ability to restrain thermal deformation of the mirror is optimized. The details are as follows:(1) Because Cu-based porous structure is hardly to sinter on Si substrate directly, the transition layer is proposed to modify the Si substrate. Thermal spraying, plasma spraying and SLS are used to fabricate the transition layer, finally the transition layer is fabricated by selective laser sintering the mixed powder of Cu, Cu-P and SiO2. The mechanism is as follows:the connection between the Si substrate and the transition layer is mixed by metallurgical-mechanical bond; the Cu3Si alloy phase generate for Cu atom interstitial diffuses into the Si substrate; the diffusion activation energy of Cu atom is reduced by P; the time in diffusion temperature window is increased by SiO2, which promote the diffusion of Cu atom; the balling of Cu-P is restrain by SiO2; the wetting tension F is increased and the wettability between Cu-P and Si substrate is improved by SiO2.(2) The porous non-deformable Si mirror is fabricated by fabricated the Cu porous structure on the transition layer on Si substrate, The law of the mirror surface thermal deformation versus time under the laser irradiation is studied by experiments. With the time of laser irradiation increases, the thermal deformations increases dramatically during0-l s, then increase slowly and arrives a constant value at last; the time for reaching the maximum thermal deformation increases with the absorbed laser intensity, when the absorbed laser intensity is5.3×105W/m2, the time to reach the maximum thermal deformation is6s; in the constant period, the thermal deformation increases with the absorbed laser intensity.(3) The thermal deformation of mirror with different porosity is analyzed by simple cubic stacking model, the simulation results show that with the porosity of the mirrors increase, the maximum thermal deformation decreases first, and then increases; The characteristic convective heat transfer length function H (dp, dn, ε) and its computational formula are proposed, the greater the value of the function H, the greater the convective heat transfer of the porous heat sink.(4) The high porosity porous non-deformation Si mirror is fabricated by adding the porogen, and the relationships of the porosity, pore size, and flexural strength of the heat sink with the addition volume of porogen are studied by using same SLS processing parameters:the porosity and pore size increase with the additional volume of porogen, and the flexural strength of the heat sink decreases with the additional volume of porogen.(5) The thermal deformation of the mirror is studied. The trend of the thermal deformation of the mirror with different porosity versus time is same; The thermal deformation of the mirror is highly sensitive to porosity; as the porosity increases, the thermal deformation decreases first, when the porosity increases to a certain extent, the thermal deformation increases, which agree well with the simulation results; The thermal deformation of mirror with43.3%porosity is253nm under the absorbed laser intensity of5.3x105W/m2...