排序方式: 共有67条查询结果,搜索用时 46 毫秒
41.
J. Cheng W. Perrie M. Sharp S. P. Edwardson N. G. Semaltianos G. Dearden K. G. Watkins 《Applied Physics A: Materials Science & Processing》2009,95(3):739-746
Picosecond laser single pulse ablation of Au, Al and Ti alloy (Ti6Al4V) was experimentally investigated with a laser pulse
width of 10 ps at a wavelength of 1064 nm for potential industrial micromachining applications. The diameters, depths and
morphologies of the drilled craters were studied. Two novel phenomena were found: as hole diameters decreased with fluence,
a change of slope of the trend line indicated a change in ablation mechanism for Al and Ti alloy, metallic materials with
short electron-phonon coupling times (<10 ps), while Au showed no such transition: an isolated island structure was also observed
on Au due to significant melt expulsion. A one-dimensional two-temperature model has been used to discriminate different ablation
phenomena. It is shown that metallic materials with different electron–phonon coupling constant have different ablation characteristics
in the ps regime. This study could be very helpful for metallic material micromachining with high repetition rate ps lasers
pulses which indicates that high throughput may be achieved as well as good machining quality. 相似文献
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180 femtoseconds (1 kHz) and 10 picoseconds (1-50 kHz) ultrafast laser micro-structuring of the metals Ti alloy, Al and Cu have been studied for the purpose of industrial application. The effects of some key laser operating parameters were investigated. The evolution of surface morphology revealed that laser pulses overlap in a range around the spatial FWHM can help to achieve optimal residual surface roughness. While observed ablation rate (unit: μm3 per pulse) changed dramatically with repetition rate due to the combined effects of plasma absorption, residual thermal energy and phase transition, higher throughput can be achieved with higher repetition rate. This study also indicated that residual surface roughness is almost independent of repetition rate at 10 ps temporal pulse length. The ablation depth is approximately proportional to the number of overscan; however, machining accuracy deteriorates, especially for femtosecond laser processing and metals with low thermal conductivity and short electron-phonon coupling time. 相似文献
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This paper obtains solitons as well as other solutions to a few nonlinear evolution equations that appear in various areas of mathematical physics. The two analytical integrators that are applied to extract solutions are tan–cot method and functional variable approaches. The soliton solutions can be used in the further study of shallow water waves in (1+1) as well as (2+1) dimensions. 相似文献
44.
O. J. Allegre W. Perrie K. Bauchert D. Liu S. P. Edwardson G. Dearden K. G. Watkins 《Applied Physics A: Materials Science & Processing》2012,107(2):445-454
The use of a fast-response, transmissive, ferroelectric liquid-crystal device for real-time control of the polarisation direction
of a femtosecond laser beam, and the benefits for various aspects of ultra-short pulse micro-machining, are discussed. Several
configurations have been used to drive the polarisation in real-time. Our microscopic investigations of the resulting features
revealed significant improvements in process efficiency and quality, compared to static linear and circular polarisations.
Following our successful micro-machining tests, real-time polarisation control could emerge as a powerful tool in laser engineering. 相似文献
45.
The interaction of 180 fs, 775 nm laser pulses with aluminium under a flowing stream of helium at ambient pressure have been used to study the material re-deposition, ablation rate and residual surface roughness. Threshold fluence Fth0.4 J cm−2 and the volume ablation rate was measured to be 30<V<450 μm3 per pulse in the fluence range 1.4<F<21 J cm−2. The presence of helium avoids gas breakdown above the substrate and leads to improved surface micro-structure by minimising surface oxidation and debris re-deposition. At 1 kHz rep. rate, with fluence F>7 J cm−2 and >85 W cm−2 average power density, residual thermal effects result in melt and debris formation producing poor surface micro-structure. On the contrary, surface micro-machining at low fluence F1.4 J cm−2 with low power density, 3 W cm−2 produces much superior surface micro-structuring with minimum melt and measured surface roughness Ra1.1±0.1 μm at a depth D50 μm. By varying the combination of fluence/scan speed during ultra-fast ablation of aluminium at 1 kHz rep. rate, results suggest that maintaining average scanned power density to <5 W cm−2 combined with single pulse fluence <4 J cm−2 produces near optimum micro-structuring. The debris under these conditions contains pure aluminium nanoparticles carried with the helium stream. 相似文献
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