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  • 79.20 D  (1)
  • PACS: 79.20.-Ds; 81.65.-b  (1)
  • 1
    ISSN: 1432-0630
    Keywords: PACS: 79.20.-Ds; 81.65.-b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. Ablation thresholds and damage behavior of cleaved and polished surfaces of CaF2, BaF2, LiF and MgF2 subjected to single-shot irradiation with 248 nm/14 ns laser pulses have been investigated using the photoacoustic mirage technique and scanning electron microscopy. For CaF2, standard polishing yields an ablation threshold of typically 20 J/cm2. When the surface is polished chemo-mechanically, the threshold can be raised to 43 J/cm2, while polishing by diamond turning leads to intermediate values around 30 J/cm2. Cleaved surfaces possess no well-defined damage threshold. When comparing different fluoride surfaces prepared by diamond turning it is found that the damage resistivity roughly scales with the band gap. We find an ablation threshold of 40 J/cm2 for diamond turned LiF while the MgF2 surface can withstand a fluence of more than 60 J/cm2 without damage. The damage topography of conventionally polished surfaces shows flaky ablation across the laser-heated area with cracks along the cleavage planes. No ablation is observed in the case of chemo- mechanical polishing; only a few cracks appear. Diamond turned surfaces show small optical absorption but mostly cracks and ablation of flakes and, in some cases, severe damage in the form of craters larger than the irradiated area. The origin of such different damage behavior is discussed.
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  • 2
    ISSN: 1432-0649
    Keywords: 79.20 D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The kinetic energy of electrons emitted due to laser interaction with a graphite surface was studied with a time-of-flight spectrometer. In addition the yields of carbon atomic and molecular ions were measured as a function of laser pulse energy. Pulse energy thresholds for ion emission are observed to correlate with the observed maximum electron energies. Furthermore, the data suggest that ionic carbon clusters can be dissociated by energetic electrons or photons created in the plasma. We believe that initially photoemitted electrons are accelerated by inverse bremsstrahlung to the energies required for electron impact ionization and dissociation
    Type of Medium: Electronic Resource
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