Formation of diversiform microstructures in wide-bandgap materials by tight-focusing femtosecond laser pulses

Fabrication of microstructures by tight-focusing intense femtosecond laser pulses into wide-bandgap materials, such as fused silica, K9 optical glass and LiNbO3 crystal, was investigated. Micrometre or sub-micrometre voids and filaments have been observed in all three wide-bandgap materials. Another microstructure, a void string, has been observed only in fused silica. The formation of micrometre or sub-micrometre voids, filaments and void strings is discussed with the multiphoton ionization process, the avalanche ionization process and the nonlinear laser pulse self-action effect when femtosecond laser pulses propagate in wide-bandgap materials.