| Microporous membranes always are used as the water separation filter in several groups of application fields, such as energy-related applications, environmental application ,industrical processes and so on.Currently,organic membranes and ceramic membranes are used in a large number of applications.But ,they have some shortcomings: lower mechanical strength and shorter lifetime.Metal membrances have the features of anti-hightemperature, anti-chemical corrosion,high mechanical strength,high anti-micro-organism, large seepage discharge, high cleaning property,narrow pore distribution,good separaring property, long service life an so on.And they have played a key role in some important field,such as energy sources,rasource and human health.Although ,mental membrances started late, their development is very rapid.At present, metal membranes which are perpared by the traditional preparation technologies have the shortcoming of the random spatial distribution of microporous ,the inhomogeneity of the porous sizes and the different depth of the porous. So An important barrier to rapid development of supported microporous membranes is also the lack of direct measurement methods to determine porosity and pore size(distribution) of the (supported) sepparation layer.The paper explorates on producting metal membranes with ultra-short laser.For the deep drilling of metals by femtosecond laser pulses ,the following processes are important: (1)laser-induced optical breakdown of air containing metal vapor and small metal particles(debris) generated by multi-pulse femtosecond laser ablation, (2) transformation of laser pulses into light filaments and (3)low-fluence finishing.compared to longer pulses ablation with ultrashort laser pulses provides two major advantage : (1) a significant reduction or complete removal of heat-affected zones. (2)the reduction of the pulses energy which is necessary to induce ablation for fixed laser wavelength and focusing conditions.Owing to the rapid progress in femtosecond laser design,microfabrication of nanostryctures with resolutions exceeding the optical diffraction limit and the improvement of contour sharpness.So metal membranes have the characteristics of uniform porous sizes, porous distribution and size can be controlled, easy to clean and the range of membrane material selection larger.Due to various advantages of the processing, femtosecond lasers are excellent and universal tools, but because of its processing small range, the high cost, it can not be used in the industry. In this paper, based on femtosecond laser interaction with the material, adjusting the ablation threshold of target by changing the surface state.Find the feasibily way to reduce the ablation threshold and product metal microporous membranes in a high processing speed.In our investigations ,a commercial femtosecond Ti:sapphire laser system is used. This laser system is able to provide 120 fs laser pulses at a wavelength of 800 nm and a 1kHz repetition rate. holes drilled in a 10-um-thick stainless steel plate. These holes were fabricated in air at atmospheric pressure using laser pulses focused by a 20-fold objective. And porous distribution is controled by the computer.Through atomic force microscopy measurements.The drilled holes have very good cylindrical geometry and high quality. The ability to fabricate such holes and holes with even more complicated shapes in a very reproducible way is remarkable.In order to reduce the larger stainless steel surface roughness (Roughness Average 6.51nm) on the impact of experimental results, the surface of stainless steel polishing techniques have been researched,firstly.And hand-polished surface will take the average roughness of about 1.5nm.Secondly, Semicontinuous metal films are produced by thermal evaporation of metal (Ag, Al)onto a stainless steel plate. Spin-coating the film of the ink in the surface of the target.The experimental results show that femtosecond laser ablation technology can prepare a smooth surface, controllable porous size and distribution of stainless steel microporous membranes. And the porous in the target on whose surface there is Semicontinuous random metal films are deeper. It shows enhanced absorption of ink surface is not obvious during ablation processing.So the main factors is the surface of particle distribution, particle size and shape.Due to the particles the large local electromagnetic fields that arise in surface-enhanced Raman scattering and Strong ?uctuations of the local fields play an important role in enhancements of a variety of nonlinear optical effects,such as four-wave mixing, nonlinear absorption and refraction, harmonic generation,ect.So the local enhancement field intensity can exceed the regional field one .In this way ,we can reduce the damage threshold. It is effective to lower the processing costs.In the paper we just primarily studied for producting metal membranes with ultra-short laser, we have a long way to go before using ultra-short laser to product metal membranes in the industry. |
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