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  • 42.10  (3)
  • 42.60  (1)
  • PACS: 52.75.Rx; 78.66.Qn; 81.60; 82.30.Lp; 83.70.Gp  (1)
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  • 1
    ISSN: 1432-0630
    Keywords: PACS: 52.75.Rx; 78.66.Qn; 81.60; 82.30.Lp; 83.70.Gp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. A single shot measurement of subpicosecond time resolution was developed to investigate the transient surface reflection changes of excimer laser ablated liquids during one UV pulse. Polysilicone oil, methyl(metacrylate), styrene, and water were irradiated by a 500 fs KrF excimer laser. The irradiated area was illuminated by an optically delayed 496 nm, 500 fs probe dye laser pulse at an incident angle of 45°. As the tilted probe beam scanned along the ablating surface, the temporal increase in the reflected intensity appeared as a spatial modulation of the probe beam. The maximum reflectivities were 1.5–2.5 times higher than those of the initial samples. The reflectivity increase is caused by a plasma mirror induced by the subpicosecond excimer laser ablation. In the case of styrene it was found that higher fluence resulted in a higher increase of reflectivity. The reflectivity enhancement was observed, both via its effect on the absorption coefficient as well as through its own photoionization by 2-photon absorption, while increasing the UV absorption of methylmetacrylate by naphthalene doping.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0630
    Keywords: 42.60 ; 78.90
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The time course of laser light induced transport of tungsten films from a glass support is followed by ultrafast photography using delayed dye laser pulses. The photographs provide unambiguous evidence that the material transport in the 40–200 mJ/cm2 intensity domain takes place via removal of solid pieces from the film material. These results are consistent with heat flow calculations which predict the overall melting of the metal layer above 380 mJ/cm2. The series of photographs presented give detailed insight into the melting process and have revealed an unexpected in-flight phase separation of solid fracture pieces and molten droplets throughout the 200–900 mJ/cm2 domain. The faster propagating molten droplets form a condensed halo in front of the solid pieces, thereby providing an efficient shield between the processing laser light and the solid phase.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 61 (1995), S. 339-345 
    ISSN: 1432-0630
    Keywords: 42.10 ; 81.60 ; 78.65 ; 85.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The processes of the ArF-excimer-laser ablation of PolyMethylMethAcrylate (PMMA) has been investigated. We studied the surface reflection of the polymer sample during UV photoablation. It was observed that a dark spot appeared in the reflected probe nitrogen laser beam (the reflection decreased below 4%) with about 5 ns delay after the onset of the ablating excimer pulse, while the transmitted probe laser intensity was increased to about 104%. A fast stroboscopic photographic arrangement was built for investigation of the ejection. A protuberance developed on the irradiated surface at about 100 ns delay. This expanded with about 600 m/s average velocity until 4 μs, then contracted slowly, and finally at 16–18 μs delay the ejection started. We also examined the process of the UV photoablation of PMMA in the vacuum chamber. In this case, the protuberance also appeared, but it left the surface nearly in one block at 3 μs delay. Using a double-flash exposure photographic arrangement based on a dye laser, the propagation velocity of the shock waves developed in the air above the surface of the PMMA sample as a function of time was measured, and good agreement with shock wave theory was found. The pressure in the shock front can be as high as 1939 bar.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0630
    Keywords: 42.80 ; 42.10 ; 81.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Reflectivity, transmission and scattering measurments in ArF (193 nm) excimer-laser irradiated polyimide are reported. The time dependence of transient changes in all three quantities were measured together for the first time, confirming a transient refractive-index change in the first 150 ns after irradiation. The relaxation time of the effect was measured and found to consist of both a fast and slow component similar to that previously reported in acoustic wave measurements. The fast decay in about 60 ns and the slow decay is 115 ns. Several potential mechanisms are examined which may explain the result.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0630
    Keywords: 42.10 ; 81.60 ; 71.30
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Experiments involving time-resolved scattering and transmission in ArF (193 nm) excimer-laser-irradiated polyimide are reported. Scattering experiments determined that constituents of the carbon layer responsible for laser-induced electrical conductivity form between 150 and 400 ns after the excimer pulse. Transmission experiments indicate that absorbing carbon is present before the formation of organized crystallites responsible for electrical conduction and scattering.
    Type of Medium: Electronic Resource
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