With the progress of national defense science and technology, the thermal effect of components in aerospace technology has greatly hindered the operation of devices. In order to solve the problem of high interface thermal resistance between materials, a new method of femtosecond processing combined with thermal interface materials was proposed to reduce interface thermal resistance. By using the high-efficiency positioning response method and the non-material selectivity and low thermal effect of femtosecond laser, the micro-structure with low roughness is precisely machined on the surface of copper based on the laser five-axis machining system, and the internal structural roughness, depth and width of the micro-structure are characterized. Then the surface is covered with thermal interface materials to achieve the purpose of reducing the interface thermal resistance between materials. At the same time, the effect of microstructure on interface thermal resistance is simulated with simulation software. A uniform array structure was obtained on the surface of copper substrate with a roughness less than 0.3μm, and the measured linear roughness of the microstructure was 0.23μm, which was consistent with the surface roughness of copper. Firstly, in order to verify that the surface heat conduction efficiency of the material with a microstructure surface is higher, the heat transfer time of the composite substrate with a microstructure is 0.0073s after simulation, which is faster than that of the composite substrate without a microstructure. Then, the thermal conductivity of the composite substrate with low roughness is 355 W·m-1 ·K-1, while that of the composite substrate with high roughness is 325 W·m-1 ·K-1 . Through the ultrafine processing, the heat transfer efficiency of the prepared composite substrate is increased by 17%, and the heat transfer efficiency is higher with lower roughness, which provides a research basis for high energy consumption devices.
As heat dispersing materials, Diamond has high thermal conductivity, extremely low coefficient of thermal expansion, low coefficient of friction, and good chemical stability, which have broad application prospects in the field of high-power device heat dissipation. This study aims to address the inability of traditional laser processing methods to meet the processing requirements of high aspect ratio diamond heat dissipation microchannels. Based on a femtosecond laser fiveaxis machining system, a five-axis attitude alternating machining method is used to study the forming size, surface roughness, and aspect ratio of femtosecond laser surface microchannels, and to compare it with the direct machining method using a galvanometer. The experimental results show that using a super depth of field optical microscope for detection, the cross-sectional shape of diamond microchannels processed using a galvanometer direct machining method is triangular, with an edge unilateral taper of 62°. The cross-sectional shape of diamond microchannels processed using a five axis attitude alternating machining method is ladder shaped, with a maximum edge unilateral taper of 88°, approaching a vertical state of 90°. As the width of microchannels increases, the unilateral taper value increases. By using a confocal microscope, the roughness of diamond microchannels processed using a galvanometer direct machining method is Ra0.88, and the optimal roughness of diamond microchannels processed using a five axis attitude alternating machining method is Ra0.29. The use of five-axis attitude alternating machining method is superior to the use of galvanometer direct machining in terms of unilateral taper and roughness. Finally, diamond rectangular microchannels were prepared using a five axis attitude alternating machining method, with a maximum aspect ratio of 10.7:1 and a maximum depth of 1.072mm.
The liquid crystal spatial light modulator is an effective method to change the quality of the laser beam light field distribution, and the phase hologram is the key to the function of the pure phase liquid crystal spatial light modulator. An improved iterative algorithm for beam shaping is proposed, which is improved on the basis of the traditional G-S algorithm. The improved algorithm is more universal, has better rapid convergence and design flexibility. By proposing an optimization factor ζ, the original uneven light intensity distribution in the light field is compensated, and the advantages of the G-S algorithm that the light field is reshaped by the clear boundary are retained and the uniformity of the light field distribution is improved. The experimental results show that the liquid crystal spatial light modulator can improve the nearfield beam quality very well, the energy utilization rate of the shaped output beam is 97%, and its top unevenness is 25.6% .
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