Morphology and mechanisms of femtosecond laser-induced structural change in bulk transparent materials

Summary form only given. When an intense femtosecond laser pulse is tightly focused into a transparent material, energy is deposited in the focal volume by nonlinear absorption. If enough energy is deposited, permanent structural change results. Characterization of the morphology of structural changes and identification of the mechanisms producing these changes represent essential steps in refining the femtosecond laser as a micromachining tool. We present a systematic study of structural changes produced in bulk glass by tightly-focused femtosecond pulses. Using optical microscopy and scanning electron microscopy (SEM), we identify a transition from a structural change mechanism dominated by localized melting or bond-break to one dominated by an explosive expansion.