4 December 2012 Dynamics of fracture inside a single crystal induced by a focused femtosecond laser pulse
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Abstract
Laser-induced deformation depends on the atomic structure of the material. In amorphous materials, the deformation is random or isotropic. On the other hand, in single crystals, anisotropic deformations occur in the specific directions, which is because of their regularly-arranged atomic structures. For example, when a fs laser pulse is focused inside rock-salt type crystalline materials (MgO, LiF, etc.) normal to the (001) plane, a void is formed in the photoexcited region and highly concentrated dislocation bands and cleavages are formed in the <110> and <100> directions, respectively. The directions of the dislocation bands and cleavages are often explained by the slip and cleavage planes of the crystals, however, stresses that induce these modifications have not been elucidated. In this study, we observed the dynamics of transient stress distributions after photoexcitation inside various single crystals by a pump-probe polarization microscope. After a femtosecond laser pulse was focused inside a MgO single crystal normal to the (001) plane, a void appeared in the photoexcited region and two stress waves (primary and secondary stress waves) were generated. In the primary stress wave, which propagated faster than the secondary one, the direction of the strain was identical to the propagation direction and the stress direction depended on the direction from the photoexcited region. In the secondary stress wave, there were tensile stresses normal to the (100) planes, which were identical to the cleavage planes.
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Masaaki Sakakura, Takaya Tochio, Yuki Ishiguro, Miki Nakabayashi, Yasuhiko Shimotsuma, Kazuyuki Hirao, and Kiyotaka Miura "Dynamics of fracture inside a single crystal induced by a focused femtosecond laser pulse", Proc. SPIE 8530, Laser-Induced Damage in Optical Materials: 2012, 853003 (4 December 2012); doi: 10.1117/12.976339; https://doi.org/10.1117/12.976339
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