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Published online by Cambridge University Press: 31 January 2011
We investigated the formation mechanism and thermal behaviors of defects which were induced at a microscopic area inside (1120) sapphire. We used a femtosecond laser having a pulse width, wavelength, and repetition rate of 238 fs, 780 nm, and 1 kHz, respectively. Cracks were formed at the focal point along the {1102} and the {1100} planes by laser irradiation. The preferential crack formation on these planes was attributed to the different surface fracture energy between the crystallographic planes of sapphire. The cracks transformed into the array of discrete pores by the subsequent heat treatment above 1300 °C, which was due to the diffusive crack healing process. In addition, dislocations were also introduced at the interface between closed cracks.